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cc88711d63
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Branches: main
Implement true multi-cons_id arm switches, i.e. switches in which we associate
more than one cons_id with a switch arm. Previously, for switches like this:
(
X = a,
goal1
;
( X = b
; X = c
),
goal2
)
we duplicated goal2. With this diff, goal2 won't be duplicated. We still
duplicate goals when that is necessary, i.e. in cases which the inner
disjunction contains code other than a functor test on the switched-on var,
like this:
(
X = a,
goal1
;
(
X = b,
goalb
;
X = c
goalc
),
goal2
)
For now, true multi-cons_id arm switches are supported only by the LLDS
backend. Supporting them on the MLDS backend is trickier, because some MLDS
target languages (e.g. Java) don't support the concept at all. So when
compiling to MLDS, we still duplicate the goal in switch detection (although
we could delay the duplication to just before code generation, if we wanted.)
compiler/options.m:
Add an internal option that tells switch detection whether to look for
multi-cons_id switch arms.
compiler/handle_options.m:
Set this option based on the back end.
Add a version of the "trans" dump level that doesn't print unification
details.
compiler/hlds_goal.m:
Extend the representation of switch cases to allow more than one
cons_id for a switch arm.
Add a type for representing switches that also includes tag information
(for use by the backends).
compiler/hlds_data.m:
For du types, record whether it is possible to speed up tests for one
cons_id (e.g. cons) by testing for the other (nil) and negating the
result. Recording this information once is faster than having
unify_gen.m trying to compute it from scratch for every single
tag test.
Add a type for representing a cons_id together with its tag.
compiler/hlds_out.m:
Print out the cheaper_tag_test information for types, and possibly
several cons_ids for each switch arm.
Add some utility predicates for describing switch arms in terms of
which cons_ids they are for.
Replace some booleans with purpose-specific types.
Make hlds_out honor is documentation, and not print out detailed
information about unifications (e.g. uniqueness and static allocation)
unless the right character ('u') is present in the control string.
compiler/add_type.m:
Fill in the information about cheaper tag tests when adding a du type.
compiler/switch_detection.m:
Extend the switch detection algorithm to detect multi-cons_id switch
arms.
When entering a switch arm, update the instmap to reflect that the
switched-on variable can now be bound only to the cons_ids that this
switch arm is for. We now need to do this, because if the arm contains
another switch on the same variable, computing the can_fail field of
that switch correctly requires us to know this information.
(Obviously, an arm for a single cons_id is unlikely to have switch on
the same variable, and for arms for several cons_ids, we previously
duplicated the arm and left the unification with the cons_id in each
copy, and this unification allowed the correct handling of any later
switches. However, the code of a multi-cons_id switch arm obviously
cannot have a unification with each cons_id in it, which is why
we now need to get the binding information from the switch itself.)
Replace some booleans with purpose-specific types, and give some
predicates better names.
compiler/instmap.m:
Provide predicates for recording that a switched-on variable has
one of several given cons_ids, for use at the starts of switch arms.
Give some predicates better names.
compiler/modes.m:
Provide predicates for updating the mode_info at the start of a
multi-cons_id switch arm.
compiler/det_report.m:
Handle multi-cons_id switch arms.
Update the instmap when entering each switch arm, since this is needed
to provide good (i.e. non-misleading) error messages when one switch on
a variable exists inside another switch on the same variable.
Since updating the instmap requires updating the module_info (since
the new inst may require a new entry in an inst table), thread the
det_info through as updateable state.
Replace some multi-clause predicate definitions with single clauses,
to make it easier to print the arguments in mdb.
Fix some misleading variable names.
compiler/det_analysis.m:
Update the instmap when entering each switch arm and thread the
det_info through as updateable state, since the predicates we call
in det_report.m require this.
compiler/det_util.m:
Handle multi-cons_id switch arms.
Rationalize the argument order of some access predicates.
compiler/switch_util.m:
Change the parts of this module that deal with string and tag switches
to optionally convert each arm to an arbitrary representation of the
arm. In the LLDS backend, the conversion process generated code for
the arm, and the arm's representation is the label at the start of
this code. This way, we can duplicate the label without duplicating
the code.
Add a new part of this module that associates each cons_id with its
tag, and (during the same pass) checks whether all the cons_ids are
integers, and if so what are min and max of these integers (needed
for dense switches). This scan is needed because the old way of making
this test had single-cons_id switch arms as one of its basic
assumptions, and doing it while adding tags to each case reduces
the number of traversals required.
Give better names to some predicates.
compiler/switch_case.m:
New module to handle the tasks associated with managing multi-cons_id
switch arms, including representing them for switch_util.m.
compiler/ll_backend.m:
Include the new module.
compiler/notes/compiler_design.html:
Note the new module.
compiler/llds.m:
Change the computed goto instruction to take a list of maybe labels
instead of a list of labels, with any missing labels meaning "not
reached".
compiler/string_switch.m:
compiler/tag_switch.m:
Reorganize the way these modules work. We can't generate the code of
each arm in place anymore, since it is now possible for more than one
cons_id to call for the execution of the same code. Instead, in
string_switch.m, we generate the codes of all the arms all at once,
and construct the hash index afterwards. (This approach simplifies
the code significantly.)
In tag switches (unlike string switches), we can get locality benefits
if the code testing for a cons_id is close to the code for that
cons_id, so we still try to put them next to each other when such
a locality benefit is available.
In both modules, the new approach uses a utility predicate in
switch_case.m to actually generate the code of each switch arm,
eliminating several copies the same code in the old versions of these
modules.
In tag_switch.m, don't create a local label that simply jumps to the
code address do_not_reached. Previously, we had to do this for
positions in jump tables that corresponded to cons_ids that the switch
variable could not be bound to. With the change to llds.m, we now
simply generate a "no" instead.
compiler/lookup_switch.m:
Get the info about int switch limits from our caller; don't compute it
here.
Give some variables better names.
compiler/dense_switch.m:
Generate the codes of the cases all at once, then assemble the table,
duplicate the labels as needed. This separation of concerns allows
significant simplifications.
Pack up all the information shared between the predicate that detects
whether a dense switch is appropriate and the predicate that actually
generates the dense switch.
Move some utility predicates to switch_util.
compiler/switch_gen.m:
Delete the code for tagging cons_ids, since that functionality is now
in switch_util.m.
The old version of this module could call the code generator to produce
(i.e. materialize) the switched-on variable repeatedly. We now produce
the variable once, and do the switch on the resulting rval.
compiler/unify_gen.m:
Use the information about cheaper tag tests in the type constructor's
entry in the HLDS type table, instead of trying to recompute it
every time.
Provide the predicates switch_gen.m now needs to perform tag tests
on rvals, as opposed to variables, and against possible more than one
cons_id.
Allow the caller to provide the tag corresponding to the cons_id(s)
in tag tests, since when we are generating code for switches, the
required computations have already been done.
Factor out some code to make all this possible.
Give better names to some predicates.
compiler/code_info.m:
Provide some utility predicates for the new code in other modules.
Give better names to some existing predicates.
compiler/hlds_code_util.m:
Rationalize the argument order of some predicates.
Replace some multi-clause predicate definitions with single clauses,
to make it easier to print the arguments in mdb.
compiler/accumulator.m:
compiler/add_heap_ops.m:
compiler/add_pragma.m:
compiler/add_trail_ops.m:
compiler/assertion.m:
compiler/build_mode_constraints.m:
compiler/check_typeclass.m:
compiler/closure_analysis.m:
compiler/code_util.m:
compiler/constraint.m:
compiler/cse_detection.m:
compiler/dead_proc_elim.m:
compiler/deep_profiling.m:
compiler/deforest.m:
compiler/delay_construct.m:
compiler/delay_partial_inst.m:
compiler/dep_par_conj.m:
compiler/distance_granularity.m:
compiler/dupproc.m:
compiler/equiv_type_hlds.m:
compiler/erl_code_gen.m:
compiler/exception_analysis.m:
compiler/export.m:
compiler/follow_code.m:
compiler/follow_vars.m:
compiler/foreign.m:
compiler/format_call.m:
compiler/frameopt.m:
compiler/goal_form.m:
compiler/goal_path.m:
compiler/goal_util.m:
compiler/granularity.m:
compiler/hhf.m:
compiler/higher_order.m:
compiler/implicit_parallelism.m:
compiler/inlining.m:
compiler/inst_check.m:
compiler/intermod.m:
compiler/interval.m:
compiler/lambda.m:
compiler/lambda.m:
compiler/lambda.m:
compiler/lco.m:
compiler/live_vars.m:
compiler/livemap.m:
compiler/liveness.m:
compiler/llds_out.m:
compiler/llds_to_x86_64.m:
compiler/loop_inv.m:
compiler/make_hlds_warn.m:
compiler/mark_static_terms.m:
compiler/middle_rec.m:
compiler/ml_tag_switch.m:
compiler/ml_type_gen.m:
compiler/ml_unify_gen.m:
compiler/mode_constraints.m:
compiler/mode_errors.m:
compiler/mode_util.m:
compiler/opt_debug.m:
compiler/opt_util.m:
compiler/pd_cost.m:
compiler/pd_into.m:
compiler/pd_util.m:
compiler/peephole.m:
compiler/polymorphism.m:
compiler/post_term_analysis.m:
compiler/post_typecheck.m:
compiler/purity.m:
compiler/quantification.m:
compiler/rbmm.actual_region_arguments.m:
compiler/rbmm.add_rbmm_goal_infos.m:
compiler/rbmm.condition_renaming.m:
compiler/rbmm.execution_paths.m:
compiler/rbmm.points_to_analysis.m:
compiler/rbmm.region_transformation.m:
compiler/recompilation.usage.m:
compiler/saved_vars.m:
compiler/simplify.m:
compiler/size_prof.m:
compiler/ssdebug.m:
compiler/store_alloc.m:
compiler/stratify.m:
compiler/structure_reuse.direct.choose_reuse.m:
compiler/structure_reuse.indirect.m:
compiler/structure_reuse.lbu.m:
compiler/structure_reuse.lfu.m:
compiler/structure_reuse.versions.m:
compiler/structure_sharing.analysis.m:
compiler/table_gen.m:
compiler/tabling_analysis.m:
compiler/term_constr_build.m:
compiler/term_norm.m:
compiler/term_pass1.m:
compiler/term_traversal.m:
compiler/trailing_analysis.m:
compiler/transform_llds.m:
compiler/tupling.m:
compiler/type_ctor_info.m:
compiler/type_util.m:
compiler/unify_proc.m:
compiler/unique_modes.m:
compiler/unneeded_code.m:
compiler/untupling.m:
compiler/unused_args.m:
compiler/unused_imports.m:
compiler/xml_documentation.m:
Make the changes necessary to conform to the changes above, principally
to handle multi-cons_id arm switches.
compiler/ml_string_switch.m:
Make the changes necessary to conform to the changes above, principally
to handle multi-cons_id arm switches.
Give some predicates better names.
compiler/dependency_graph.m:
Make the changes necessary to conform to the changes above, principally
to handle multi-cons_id arm switches. Change the order of arguments
of some predicates to make this easier.
compiler/bytecode.m:
compiler/bytecode_data.m:
compiler/bytecode_gen.m:
Make the changes necessary to conform to the changes above, principally
to handle multi-cons_id arm switches. (The bytecode interpreter
has not been updated.)
compiler/prog_rep.m:
mdbcomp/program_representation.m:
Change the byte sequence representation of goals to allow switch arms
with more than one cons_id. compiler/prog_rep.m now writes out the
updated representation, while mdbcomp/program_representation.m reads in
the updated representation.
deep_profiler/mdbprof_procrep.m:
Conform to the updated program representation.
tools/binary:
Fix a bug: if the -D option was given, the stage 2 directory wasn't
being initialized.
Abort if users try to give that option more than once.
compiler/Mercury.options:
Work around bug #32 in Mantis.
1787 lines
59 KiB
HTML
1787 lines
59 KiB
HTML
<html>
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<head>
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<title>
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Notes On The Design Of The Mercury Compiler
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</title>
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</head>
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<body bgcolor="#ffffff" text="#000000">
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<hr>
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<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
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<p>
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This file contains an overview of the design of the compiler.
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<p>
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See also <a href="overall_design.html">overall_design.html</a>
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for an overview of how the different sub-systems (compiler,
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library, runtime, etc.) fit together.
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<hr>
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<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
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<h2> OUTLINE </h2>
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<p>
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The main job of the compiler is to translate Mercury into C, although it
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can also translate (subsets of) Mercury to some other languages:
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Mercury bytecode (for a planned bytecode interpreter) and MSIL (for the
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Microsoft .NET platform).
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<p>
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The top-level of the compiler is in the file mercury_compile.m,
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which is a sub-module of the top_level.m package.
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The basic design is that compilation is broken into the following
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stages:
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<ul>
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<li> 1. parsing (source files -> HLDS)
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<li> 2. semantic analysis and error checking (HLDS -> annotated HLDS)
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<li> 3. high-level transformations (annotated HLDS -> annotated HLDS)
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<li> 4. code generation (annotated HLDS -> target representation)
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<li> 5. low-level optimizations
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(target representation -> target representation)
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<li> 6. output code (target representation -> target code)
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</ul>
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<p>
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Note that in reality the separation is not quite as simple as that.
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Although parsing is listed as step 1 and semantic analysis is listed
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as step 2, the last stage of parsing actually includes some semantic checks.
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And although optimization is listed as steps 3 and 5, it also occurs in
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steps 2, 4, and 6. For example, elimination of assignments to dead
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variables is done in mode analysis; middle-recursion optimization and
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the use of static constants for ground terms is done in code
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generation; and a few low-level optimizations are done in llds_out.m
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as we are spitting out the C code.
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<p>
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In addition, the compiler is actually a multi-targeted compiler
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with several different back-ends.
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<p>
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The modules in the compiler are structured by being grouped into
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"packages". A "package" is just a meta-module,
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i.e. a module that contains other modules as sub-modules.
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(The sub-modules are almost always stored in separate files,
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which are named only for their final module name.)
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We have a package for the top-level, a package for each main pass, and
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finally there are also some packages for library modules that are used
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by more than one pass.
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<p>
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Taking all this into account, the structure looks like this:
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<ul type=disc>
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<li> At the top of the dependency graph is the top_level.m package,
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which currently contains only the one module mercury_compile.m
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which invokes all the different passes in the compiler.
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<li> The next level down is all of the different passes of the compiler.
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In general, we try to stick by the principle that later passes can
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depend on data structures defined in earlier passes, but not vice
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versa.
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<ul type=disc>
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<li> front-end
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<ul type=disc>
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<li> 1. parsing (source files -> HLDS)
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<br> Packages: parse_tree.m and hlds.m
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<li> 2. semantic analysis and error checking
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(HLDS -> annotated HLDS)
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<br> Package: check_hlds.m
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<li> 3. high-level transformations
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(annotated HLDS -> annotated HLDS)
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<br> Package: transform_hlds.m
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</ul>
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<li> back-ends
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<ul type=disc>
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<li> a. LLDS back-end
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<br> Package: ll_backend.m
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<ul type=disc>
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<li> 3a. LLDS-back-end-specific HLDS->HLDS transformations
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<li> 4a. code generation (annotated HLDS -> LLDS)
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<li> 5a. low-level optimizations (LLDS -> LLDS)
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<li> 6a. output code (LLDS -> C)
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</ul>
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<li> b. MLDS back-end
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<br> Package: ml_backend.m
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<ul type=disc>
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<li> 4b. code generation (annotated HLDS -> MLDS)
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<li> 5b. MLDS transformations (MLDS -> MLDS)
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<li> 6b. output code
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(MLDS -> C or MLDS -> MSIL or MLDS -> Java, etc.)
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</ul>
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<li> c. bytecode back-end
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<br> Package: bytecode_backend.m
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<ul type=disc>
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<li> 4c. code generation (annotated HLDS -> bytecode)
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</ul>
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<li> d. Erlang back-end
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<br> Package: erl_backend.m
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<ul type=disc>
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<li> 4d. code generation (annotated HLDS -> ELDS)
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<li> 6d. output code
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(ELDS -> Erlang)
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</ul>
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<li> There's also a package backend_libs.m which contains
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modules which are shared between several different back-ends.
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</ul>
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</ul>
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<li> Finally, at the bottom of the dependency graph there is the package
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libs.m. libs.m contains the option handling code, and also library
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modules which are not sufficiently general or sufficiently useful to
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go in the Mercury standard library.
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</ul>
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<p>
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In addition to the packages mentioned above, there are also packages
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for the build system: make.m contains the support for the `--make' option,
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and recompilation.m contains the support for the `--smart-recompilation'
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option.
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<hr>
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<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
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<h2> DETAILED DESIGN </h2>
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<p>
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This section describes the role of each module in the compiler.
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For more information about the design of a particular module,
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see the documentation at the start of that module's source code.
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<hr>
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<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
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<p>
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The action is co-ordinated from mercury_compile.m or make.m (if `--make'
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was specified on the command line).
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<h3> Option handling </h3>
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<p>
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Option handling is part of the libs.m package.
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<p>
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The command-line options are defined in the module options.m.
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mercury_compile.m calls library/getopt.m, passing the predicates
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defined in options.m as arguments, to parse them. It then invokes
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handle_options.m to postprocess the option set. The results are
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stored in the io.state, using the type globals defined in globals.m.
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<h3> Build system </h3>
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<p>
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Support for `--make' is in the make.m package,
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which contains the following modules:
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<dl>
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<dt> make.m
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<dd>
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Categorizes targets passed on the command line and passes
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them to the appropriate module to be built.
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<dt> make.program_target.m
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<dd>
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Handles whole program `mmc --make' targets, including
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executables, libraries and cleanup.
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<dt> make.module_target.m
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<dd>
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Handles targets built by a compilation action associated
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with a single module, for example making interface files,
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<dt> make.dependencies.m
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<dd>
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Compute dependencies between targets and between modules.
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<dt> make.module_dep_file.m
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<dd>
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Record the dependency information for each module between
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compilations.
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<dt> make.util.m
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<dd>
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Utility predicates.
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<dt> options_file.m
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<dd>
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Read the options files specified by the `--options-file'
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option. Also used by mercury_compile.m to collect the value
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of DEFAULT_MCFLAGS, which contains the auto-configured flags
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passed to the compiler.
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</dl>
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The build process also invokes routines in compile_target_code.m,
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which is part of the backend_libs.m package (see below).
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<p>
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<hr>
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<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
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<h3> FRONT END </h3>
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<h4> 1. Parsing </h4>
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<h5> The parse_tree.m package </h5>
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<p>
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The first part of parsing is in the parse_tree.m package,
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which contains the modules listed below
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(except for the library/*.m modules,
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which are in the standard library).
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This part produces the parse_tree.m data structure,
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which is intended to match up as closely as possible
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with the source code, so that it is suitable for tasks
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such as pretty-printing.
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<p>
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<ul>
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<li> <p> lexical analysis (library/lexer.m)
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<li> <p> stage 1 parsing - convert strings to terms. <p>
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library/parser.m contains the code to do this, while
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library/term.m and library/varset.m contain the term and varset
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data structures that result, and predicates for manipulating them.
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<li> <p> stage 2 parsing - convert terms to `items'
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(declarations, clauses, etc.)
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<p>
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The result of this stage is a parse tree that has a one-to-one
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correspondence with the source code. The parse tree data structure
|
|
definition is in prog_data.m and prog_item.m, while the code to create
|
|
it is in prog_io.m and its submodules prog_io_dcg.m (which handles
|
|
clauses using Definite Clause Grammar notation), prog_io_goal.m (which
|
|
handles goals), prog_io_pragma.m (which handles pragma declarations),
|
|
prog_io_typeclass.m (which handles typeclass and instance
|
|
declarations) and prog_io_util.m (which defines predicates and types
|
|
needed by the other prog_io*.m modules.
|
|
|
|
<p>
|
|
|
|
The modules prog_out.m and mercury_to_mercury.m contain predicates
|
|
for printing the parse tree.
|
|
prog_util.m contains some utility predicates
|
|
for manipulating the parse tree,
|
|
prog_mode contains utility predicates
|
|
for manipulating insts and modes,
|
|
prog_type contains utility predicates
|
|
for manipulating types,
|
|
prog_type_subst contains predicates
|
|
for performing substitutions on types,
|
|
prog_foreign contains utility predicates
|
|
for manipulating foreign code,
|
|
prog_mutable contains utility predicates
|
|
for manipulating mutable variables,
|
|
prog_event contains utility predicates for working with events,
|
|
while error_util.m contains predicates
|
|
for printing nicely formatting error messages.
|
|
|
|
<li><p> imports and exports are handled at this point (modules.m)
|
|
|
|
<p>
|
|
modules.m has the code to write out `.int', `.int2', `.int3',
|
|
`.d' and `.dep' files.
|
|
|
|
<p>
|
|
source_file_map.m contains code to read, write and search
|
|
the mapping between module names and file names.
|
|
|
|
<li><p> module qualification of types, insts and modes
|
|
|
|
<p>
|
|
module_qual.m - <br>
|
|
Adds module qualifiers to all types insts and modes,
|
|
checking that a given type, inst or mode exists and that
|
|
there is only possible match. This is done here because
|
|
it must be done before the `.int' and `.int2' interface files
|
|
are written. This also checks whether imports are really needed
|
|
in the interface.
|
|
|
|
<p>
|
|
Notes on module qualification:
|
|
<ul>
|
|
<li> all types, typeclasses, insts and modes occurring in pred, func,
|
|
type, typeclass and mode declarations are module qualified by
|
|
module_qual.m.
|
|
<li> all types, insts and modes occurring in lambda expressions,
|
|
explicit type qualifications, and clause mode annotations
|
|
are module qualified in make_hlds.m.
|
|
<li> constructors occurring in predicate and function mode declarations
|
|
are module qualified during type checking.
|
|
<li> predicate and function calls and constructors within goals
|
|
are module qualified during mode analysis.
|
|
</ul>
|
|
|
|
|
|
<li><p> reading and writing of optimization interfaces
|
|
(intermod.m and trans_opt.m -- these are part of the
|
|
hlds.m package, not the parse_tree.m package).
|
|
|
|
<p>
|
|
<module>.opt contains clauses for exported preds suitable for
|
|
inlining or higher-order specialization. The `.opt' file for the
|
|
current module is written after type-checking. `.opt' files
|
|
for imported modules are read here.
|
|
<module>.opt contains termination analysis information
|
|
for exported preds (eventually it ought to contain other
|
|
"transitive" information too, e.g. for optimization, but
|
|
currently it is only used for termination analysis).
|
|
`.trans_opt' files for imported modules are read here.
|
|
The `.trans_opt' file for the current module is written
|
|
after the end of semantic analysis.
|
|
|
|
<li><p> expansion of equivalence types (equiv_type.m)
|
|
|
|
<p>
|
|
`with_type` and `with_inst` annotations on predicate
|
|
and function type and mode declarations are also expanded.
|
|
|
|
<p>
|
|
Expansion of equivalence types is really part of type-checking,
|
|
but is done on the item_list rather than on the HLDS because it
|
|
turned out to be much easier to implement that way.
|
|
</ul>
|
|
|
|
<p>
|
|
That's all the modules in the parse_tree.m package.
|
|
|
|
<h5> The hlds.m package </h5>
|
|
<p>
|
|
Once the stages listed above are complete, we then convert from the parse_tree
|
|
data structure to a simplified data structure, which no longer attempts
|
|
to maintain a one-to-one correspondence with the source code.
|
|
This simplified data structure is called the High Level Data Structure (HLDS),
|
|
which is defined in the hlds.m package.
|
|
|
|
<p>
|
|
The last stage of parsing is this conversion to HLDS,
|
|
which is done mostly by the following submodules
|
|
of the make_hlds module in the hlds package.
|
|
<dl>
|
|
|
|
<dt>
|
|
make_hlds_passes.m
|
|
<dd>
|
|
This submodule calls the others to perform the conversion, in several passes.
|
|
(We cannot do everything in one pass;
|
|
for example, we need to have seen a predicate's declaration
|
|
before we can process its clauses.)
|
|
|
|
<dt>
|
|
superhomogeneous.m
|
|
<dd>
|
|
Performs the conversion of unifications into superhomogeneous form.
|
|
|
|
<dt>
|
|
state_var.m
|
|
<dd>
|
|
Expands away state variable syntax.
|
|
|
|
<dt>
|
|
field_access.m
|
|
<dd>
|
|
Expands away field access syntax.
|
|
|
|
<dt>
|
|
add_clause.m
|
|
<dd>
|
|
Converts clauses from parse_tree format to hlds format.
|
|
Handles their addition to procedures,
|
|
which is nontrivial in the presence of mode-specific clauses.
|
|
Eliminates universal quantification
|
|
(using `all [Vs] G' ===> `not (some [Vs] (not G))')
|
|
and implication (using `A => B' ===> `not(A, not B)').
|
|
|
|
<dt>
|
|
add_pred.m
|
|
<dd>
|
|
Handles type and mode declarations for predicates.
|
|
|
|
<dt>
|
|
add_type.m
|
|
<dd>
|
|
Handles the declarations of types.
|
|
|
|
<dt>
|
|
add_mode.m
|
|
<dd>
|
|
Handles the declarations of insts and modes,
|
|
including checking for circular insts and modes.
|
|
|
|
<dt>
|
|
add_special_pred.m
|
|
<dd>
|
|
Adds unify, compare, and (if needed) index and init predicates
|
|
to the HLDS as necessary.
|
|
|
|
<dt>
|
|
add_solver.m
|
|
<dd>
|
|
Adds the casting predicates needed by solver types to the HLDS as necessary.
|
|
|
|
<dt>
|
|
add_class.m
|
|
<dd>
|
|
Handles typeclass and instance declarations.
|
|
|
|
<dt>
|
|
qual_info.m
|
|
<dd>
|
|
Handles the abstract data types used for module qualification.
|
|
|
|
<dt>
|
|
make_hlds_warn.m
|
|
<dd>
|
|
Looks for constructs that merit warnings,
|
|
such as singleton variables and variables with overlapping scopes.
|
|
|
|
<dt>
|
|
make_hlds_error.m
|
|
<dd>
|
|
Error messages used by more than one submodule of make_hlds.m.
|
|
|
|
<dt>
|
|
add_pragma.m
|
|
<dd>
|
|
Adds most kinds of pragmas to the HLDS,
|
|
including import/export pragmas, tabling pragmas and foreign code.
|
|
|
|
</dl>
|
|
|
|
Fact table pragmas are handled by fact_table.m
|
|
(which is part of the ll_backend.m package).
|
|
That module also reads the facts from the declared file
|
|
and compiles them into a separate C file
|
|
used by the foreign_proc body of the relevant predicate.
|
|
|
|
The conversion of the item list to HLDS also involves make_tags.m,
|
|
which chooses the data representation for each discriminated union type
|
|
by assigning tags to each functor.
|
|
|
|
<p>
|
|
The HLDS data structure itself is spread over the following modules:
|
|
|
|
<ol>
|
|
<li>
|
|
hlds_args.m defines the parts of the HLDS concerned with predicate
|
|
and function argument lists.
|
|
<li>
|
|
hlds_data.m defines the parts of the HLDS concerned with
|
|
function symbols, types, insts, modes and determinisms;
|
|
<li>
|
|
hlds_goal.m defines the part of the HLDS concerned with the
|
|
structure of goals, including the annotations on goals.
|
|
<li>
|
|
hlds_clauses.m defines the part of the HLDS concerning clauses.
|
|
<li>
|
|
hlds_rtti.m defines the part of the HLDS concerning RTTI.
|
|
<li>
|
|
hlds_pred.m defines the part of the HLDS concerning predicates and procedures;
|
|
<li>
|
|
pred_table.m defines the tables that index predicates and functions
|
|
on various combinations of (qualified and unqualified) names and arity.
|
|
<li>
|
|
hlds_module.m defines the top-level parts of the HLDS,
|
|
including the type module_info.
|
|
</ol>
|
|
|
|
<p>
|
|
The module hlds_out.m contains predicates to dump the HLDS to a file.
|
|
|
|
<p>
|
|
The hlds.m package also contains some utility modules that contain
|
|
various library routines which are used by other modules that manipulate
|
|
the HLDS:
|
|
|
|
<dl>
|
|
<dt> hlds_code_util.m
|
|
<dd> Utility routines for use during HLDS generation.
|
|
|
|
<dt> goal_form.m
|
|
<dd> Contains predicates for determining whether
|
|
HLDS goals match various criteria.
|
|
|
|
<dt> goal_util.m
|
|
<dd> Contains various miscellaneous utility predicates for manipulating
|
|
HLDS goals, e.g. for renaming variables.
|
|
|
|
<dt> passes_aux.m
|
|
<dd> Contains code to write progress messages, and higher-order code
|
|
to traverse all the predicates defined in the current module
|
|
and do something with each one.
|
|
|
|
<dt> hlds_error_util.m:
|
|
<dd> Utility routines for printing nicely formatted error messages
|
|
for symptoms involving HLDS data structures.
|
|
For symptoms involving only structures defined in prog_data,
|
|
use parse_tree.error_util.
|
|
|
|
<dt> code_model.m:
|
|
<dd> Defines a type for classifying determinisms
|
|
in ways useful to the various backends,
|
|
and utility predicates on that type.
|
|
|
|
<dt> arg_info.m:
|
|
<dd> Utility routines that the various backends use
|
|
to analyze procedures' argument lists
|
|
and decide on parameter passing conventions.
|
|
|
|
<dt> hhf.m:
|
|
<dd> Facilities for translating the bodies of predicates
|
|
to hyperhomogeneous form, for constraint based mode analysis.
|
|
|
|
<dt> inst_graph.m:
|
|
<dd> Defines the inst_graph data type,
|
|
which describes the structures of insts for constraint based mode analysis,
|
|
as well as predicates operating on that type.
|
|
</dl>
|
|
|
|
<h4> 2. Semantic analysis and error checking </h4>
|
|
|
|
<p>
|
|
This is the check_hlds.m package,
|
|
with support from the mode_robdd.m package for constraint based mode analysis.
|
|
|
|
<p>
|
|
|
|
Any pass which can report errors or warnings must be part of this stage,
|
|
so that the compiler does the right thing for options such as
|
|
`--halt-at-warn' (which turns warnings into errors) and
|
|
`--error-check-only' (which makes the compiler only compile up to this stage).
|
|
|
|
<dl>
|
|
|
|
<dt> implicit quantification
|
|
|
|
<dd>
|
|
quantification.m (XXX which for some reason is part of the hlds.m
|
|
package rather than the check_hlds.m package)
|
|
handles implicit quantification and computes
|
|
the set of non-local variables for each sub-goal.
|
|
It also expands away bi-implication (unlike the expansion
|
|
of implication and universal quantification, this expansion
|
|
cannot be done until after quantification).
|
|
This pass is called from the `transform' predicate in make_hlds.m.
|
|
<p>
|
|
|
|
<dt> checking typeclass instances (check_typeclass.m)
|
|
<dd>
|
|
check_typeclass.m both checks that instance declarations satisfy all
|
|
the appropriate superclass constraints
|
|
(including functional dependencies)
|
|
and performs a source-to-source transformation on the
|
|
methods from the instance declarations.
|
|
The transformed code is checked for type, mode, uniqueness, purity
|
|
and determinism correctness by the later passes, which has the effect
|
|
of checking the correctness of the instance methods themselves
|
|
(ie. that the instance methods match those expected by the typeclass
|
|
declaration).
|
|
During the transformation,
|
|
pred_ids and proc_ids are assigned to the methods for each instance.
|
|
|
|
<p>
|
|
While checking that the superclasses of a class are satisfied
|
|
by the instance declaration, a set of constraint_proofs are built up
|
|
for the superclass constraints. These are used by polymorphism.m when
|
|
generating the base_typeclass_info for the instance.
|
|
|
|
<p>
|
|
This module also checks that there are no ambiguous pred/func
|
|
declarations (that is, it checks that all type variables in constraints
|
|
are determined by type variables in arguments),
|
|
checks that there are no cycles in the typeclass hierarchy,
|
|
and checks that each abstract instance has a corresponding
|
|
typeclass instance.
|
|
<p>
|
|
|
|
<dt> check user defined insts for consistency with types
|
|
<dd>
|
|
inst_check.m checks that all user defined bound insts are consistent
|
|
with at least one type in scope
|
|
(i.e. that the set of function symbols
|
|
in the bound list for the inst are a subset of the allowed function
|
|
symbols for at least one type in scope).
|
|
|
|
<p>
|
|
A warning is issued if it finds any user defined bound insts not
|
|
consistent with any types in scope.
|
|
<p>
|
|
|
|
<dt> improving the names of head variables
|
|
<dd>
|
|
headvar_names.m tries to replace names of the form HeadVar__n
|
|
with actual names given by the programmer.
|
|
<p>
|
|
For efficiency, this phase not a standalone pass,
|
|
but is instead invoked by the typechecker.
|
|
|
|
<dt> type checking
|
|
|
|
<dd>
|
|
<ul>
|
|
<li> typecheck.m handles type checking, overloading resolution &
|
|
module name resolution, and almost fully qualifies all predicate
|
|
and functor names. It sets the map(var, type) field in the
|
|
pred_info. However, typecheck.m doesn't figure out the pred_id
|
|
for function calls or calls to overloaded predicates; that can't
|
|
be done in a single pass of typechecking, and so it is done
|
|
later on (in post_typecheck.m, for both preds and function calls)
|
|
<li> typecheck_info.m defines the main data structures used by
|
|
typechecking.
|
|
<li> typecheck_errors.m handles outputting of type errors.
|
|
<li> typeclasses.m checks typeclass constraints, and
|
|
any redundant constraints that are eliminated are recorded (as
|
|
constraint_proofs) in the pred_info for future reference.
|
|
<li> type_util.m contains utility predicates dealing with types
|
|
that are used in a variety of different places within the compiler
|
|
<li> post_typecheck.m may also be considered to logically be a part
|
|
of typechecking, but it is actually called from purity
|
|
analysis (see below). It contains the stuff related to
|
|
type checking that can't be done in the main type checking pass.
|
|
It also removes assertions from further processing.
|
|
post_typecheck.m reports errors for unbound type and inst variables,
|
|
for unsatisfied type class constraints and for indistinguishable
|
|
predicate or function modes.
|
|
</ul>
|
|
<p>
|
|
|
|
<dt> assertions
|
|
|
|
<dd>
|
|
assertion.m (XXX in the hlds.m package)
|
|
is the abstract interface to the assertion table.
|
|
Currently all the compiler does is type check the assertions and
|
|
record for each predicate that is used in an assertion, which
|
|
assertion it is used in. The set up of the assertion table occurs
|
|
in post_typecheck.finish_assertion.
|
|
<p>
|
|
|
|
<dt> purity analysis
|
|
|
|
<dd>
|
|
purity.m is responsible for purity checking, as well as
|
|
defining the <CODE>purity</CODE> type and a few public
|
|
operations on it. It also calls post_typecheck.m to
|
|
complete the handling of predicate
|
|
overloading for cases which typecheck.m is unable to handle,
|
|
and to check for unbound type variables.
|
|
Elimination of double negation is also done here; that needs to
|
|
be done after quantification analysis and before mode analysis.
|
|
Calls to `private_builtin.unsafe_type_cast/2' are converted
|
|
into `generic_call(unsafe_cast, ...)' goals here.
|
|
<p>
|
|
|
|
<dt> polymorphism transformation
|
|
|
|
<dd>
|
|
polymorphism.m handles introduction of type_info arguments for
|
|
polymorphic predicates and introduction of typeclass_info arguments
|
|
for typeclass-constrained predicates.
|
|
This phase needs to come before mode analysis so that mode analysis
|
|
can properly reorder code involving existential types.
|
|
(It also needs to come before simplification so that simplify.m's
|
|
optimization of goals with no output variables doesn't do the
|
|
wrong thing for goals whose only output is the type_info for
|
|
an existentially quantified type parameter.)
|
|
<p>
|
|
This phase also
|
|
converts higher-order predicate terms into lambda expressions,
|
|
and copies the clauses to the proc_infos in preparation for
|
|
mode analysis.
|
|
<p>
|
|
The polymorphism.m module also exports some utility routines that
|
|
are used by other modules. These include some routines for generating
|
|
code to create type_infos, which are used by simplify.m and magic.m
|
|
when those modules introduce new calls to polymorphic procedures.
|
|
<p>
|
|
When it has finished, polymorphism.m calls clause_to_proc.m to
|
|
make duplicate copies of the clauses for each different mode of
|
|
a predicate; all later stages work on procedures, not predicates.
|
|
<p>
|
|
|
|
<dt> mode analysis
|
|
|
|
<dd>
|
|
<ul>
|
|
<li> modes.m is the main mode analysis module.
|
|
It checks that the code is mode-correct, reordering it
|
|
if necessary, and annotates each goal with a delta-instmap
|
|
that specifies the changes in instantiatedness of each
|
|
variable over that goal.
|
|
<li> modecheck_unify.m is the sub-module which analyses
|
|
unification goals.
|
|
It also module qualifies data constructors.
|
|
<li> modecheck_call.m is the sub-module which analyses calls.
|
|
|
|
<p>
|
|
|
|
The following sub-modules are used:
|
|
<dl>
|
|
<dt> mode_info.m
|
|
<dd>
|
|
(the main data structure for mode analysis)
|
|
<dt> delay_info.m
|
|
<dd>
|
|
(a sub-component of the mode_info data
|
|
structure used for storing the information
|
|
for scheduling: which goals are currently
|
|
delayed, what variables they are delayed on, etc.)
|
|
<dt> instmap.m (XXX in the hlds.m package)
|
|
<dd>
|
|
Defines the instmap and instmap_delta ADTs
|
|
which store information on what instantiations
|
|
a set of variables may be bound to.
|
|
<dt> inst_match.m
|
|
<dd>
|
|
This contains the code for examining insts and
|
|
checking whether they match.
|
|
<dt> inst_util.m
|
|
<dd>
|
|
This contains the code for creating new insts from
|
|
old ones: unifying them, merging them and so on.
|
|
<dt> mode_errors.m
|
|
<dd>
|
|
This module contains all the code to
|
|
print error messages for mode errors
|
|
</dl>
|
|
<li> mode_util.m contains miscellaneous useful predicates dealing
|
|
with modes (many of these are used by lots of later stages
|
|
of the compiler)
|
|
<li> mode_debug.m contains utility code for tracing the actions
|
|
of the mode checker.
|
|
<li> delay_partial_inst.m adds a post-processing pass on mode-correct
|
|
procedures to avoid creating intermediate, partially instantiated
|
|
data structures.
|
|
</ul>
|
|
<p>
|
|
|
|
<dt> constraint based mode analysis
|
|
|
|
<dd> This is an experimental alternative
|
|
to the usual mode analysis algorithm.
|
|
It works by building a system of boolean constraints
|
|
about where (parts of) variables can be bound,
|
|
and then solving those constraints.
|
|
|
|
<ul>
|
|
<li> mode_constraints.m is the module that finds the constraints
|
|
and adds them to the constraint store.
|
|
<li> mode_ordering.m is the module that uses solutions of the
|
|
constraint system to find an ordering for the goals in conjunctions.
|
|
<li> mode_constraint_robdd.m is the interface to the modules
|
|
that perform constraint solving using reduced ordered binary decision
|
|
diagrams (robdds).
|
|
<li> We have several implementations of solvers using robdds.
|
|
Each solver is in a module named mode_robdd.X.m, and they all belong
|
|
to the top-level mode_robdd.m.
|
|
</ul>
|
|
<p>
|
|
|
|
<dt> constraint based mode analysis propagation solver
|
|
|
|
<dd> This is a new alternative
|
|
for the constraint based mode analysis algorithm.
|
|
It will perform conjunct reordering for mercury
|
|
programs of a limited syntax (it calls error if
|
|
it encounters higher order code or a parallel
|
|
conjunction, or is asked to infer modes).
|
|
|
|
|
|
<ul>
|
|
<li> prop_mode_constraints.m is the interface to the old
|
|
mode_constraints.m. It builds constraints for an SCC.
|
|
<li> build_mode_constraints.m is the module that traverses a predicate
|
|
to build constraints for it.
|
|
<li> abstract_mode_constraints.m describes data structures for the
|
|
constraints themselves.
|
|
<li> ordering_mode_constraints.m solves constraints to determine
|
|
the producing and consuming goals for program variables, and
|
|
performs conjunct reordering based on the result.
|
|
<li> mcsolver.m contains the constraint solver used by
|
|
ordering_mode_constraints.m.
|
|
</ul>
|
|
<p>
|
|
|
|
<dt> indexing and determinism analysis
|
|
|
|
<dd>
|
|
<ul>
|
|
<li> switch_detection.m transforms into switches those disjunctions
|
|
in which several disjuncts test the same variable against different
|
|
function symbols.
|
|
<li> cse_detection.m looks for disjunctions in which each disjunct tests
|
|
the same variable against the same function symbols, and hoists any
|
|
such unifications out of the disjunction.
|
|
If cse_detection.m modifies the code,
|
|
it will re-run mode analysis and switch detection.
|
|
<li> det_analysis.m annotates each goal with its determinism;
|
|
it inserts cuts in the form of "some" goals wherever the determinisms
|
|
and delta instantiations of the goals involved make it necessary.
|
|
Any errors found during determinism analysis are reported by
|
|
det_report.m.
|
|
det_util.m contains utility predicates used in several modules.
|
|
</ul>
|
|
<p>
|
|
|
|
<dt> checking of unique modes (unique_modes.m)
|
|
|
|
<dd>
|
|
unique_modes.m checks that non-backtrackable unique modes were
|
|
not used in a context which might require backtracking.
|
|
Note that what unique_modes.m does is quite similar to
|
|
what modes.m does, and unique_modes calls lots of predicates
|
|
defined in modes.m to do it.
|
|
<p>
|
|
|
|
<dt> stratification checking
|
|
|
|
<dd>
|
|
The module stratify.m implements the `--warn-non-stratification'
|
|
warning, which is an optional warning that checks for loops
|
|
through negation.
|
|
<p>
|
|
|
|
<dt> simplification (simplify.m)
|
|
|
|
<dd>
|
|
simplify.m finds and exploits opportunities for simplifying the
|
|
internal form of the program, both to optimize the code and to
|
|
massage the code into a form the code generator will accept.
|
|
It also warns the programmer about any constructs that are so simple
|
|
that they should not have been included in the program in the first
|
|
place. (That's why this pass needs to be part of semantic analysis:
|
|
because it can report warnings.)
|
|
simplify.m converts complicated unifications into procedure calls.
|
|
simplify.m calls common.m which looks for (a) construction unifications
|
|
that construct a term that is the same as one that already exists,
|
|
or (b) repeated calls to a predicate with the same inputs, and replaces
|
|
them with assignment unifications.
|
|
simplify.m also attempts to partially evaluate calls to builtin
|
|
procedures if the inputs are all constants (this is const_prop.m
|
|
in the transform_hlds.m package).
|
|
simplify.m also calls format_call.m to look for
|
|
(possibly) incorrect uses of string.format io.format.
|
|
<p>
|
|
|
|
<dt> unused imports (unused_imports.m)
|
|
|
|
<dd>
|
|
unused_imports.m determines which imports of the module
|
|
are not required for the module to compile. It also identifies
|
|
which imports of a module can be moved from the interface to the
|
|
implementation.
|
|
<p>
|
|
|
|
<dt> xml documentation (xml_documentation.m)
|
|
|
|
<dd>
|
|
xml_documentation.m outputs a XML representation of all the
|
|
declarations in the module. This XML representation is designed
|
|
to be transformed via XSL into more human readable documentation.
|
|
<p>
|
|
|
|
</dl>
|
|
|
|
<h4> 3. High-level transformations </h4>
|
|
|
|
<p>
|
|
This is the transform_hlds.m package.
|
|
|
|
<p>
|
|
|
|
The first pass of this stage does tabling transformations (table_gen.m).
|
|
This involves the insertion of several calls to tabling predicates
|
|
defined in mercury_builtin.m and the addition of some scaffolding structure.
|
|
Note that this pass can change the evaluation methods of some procedures to
|
|
eval_table_io, so it should come before any passes that require definitive
|
|
evaluation methods (e.g. inlining).
|
|
|
|
<p>
|
|
|
|
The next pass of this stage is a code simplification, namely
|
|
removal of lambda expressions (lambda.m):
|
|
|
|
<ul>
|
|
<li>
|
|
lambda.m converts lambda expressions into higher-order predicate
|
|
terms referring to freshly introduced separate predicates.
|
|
This pass needs to come after unique_modes.m to ensure that
|
|
the modes we give to the introduced predicates are correct.
|
|
It also needs to come after polymorphism.m since polymorphism.m
|
|
doesn't handle higher-order predicate constants.
|
|
</ul>
|
|
|
|
(Is there any good reason why lambda.m comes after table_gen.m?)
|
|
|
|
|
|
<p>
|
|
|
|
Expansion of equivalence types (equiv_type_hlds.m)
|
|
|
|
<ul>
|
|
<li>
|
|
This pass expands equivalences which are not meant to
|
|
be visible to the user of imported modules. This
|
|
is necessary for the IL back-end and in some cases
|
|
for `:- pragma export' involving foreign types on
|
|
the C back-end.
|
|
|
|
<p>
|
|
|
|
It's also needed by the MLDS->C back-end, for
|
|
--high-level-data, and for cases involving abstract
|
|
equivalence types which are defined as "float".
|
|
</ul>
|
|
|
|
<p>
|
|
|
|
Exception analysis. (exception_analysis.m)
|
|
|
|
<ul>
|
|
<li>
|
|
This pass annotates each module with information about whether
|
|
the procedures in the module may throw an exception or not.
|
|
</ul>
|
|
|
|
<p>
|
|
|
|
The next pass is termination analysis. The various modules involved are:
|
|
|
|
<ul>
|
|
<li>
|
|
termination.m is the control module. It sets the argument size and
|
|
termination properties of builtin and compiler generated procedures,
|
|
invokes term_pass1.m and term_pass2.m
|
|
and writes .trans_opt files and error messages as appropriate.
|
|
<li>
|
|
term_pass1.m analyzes the argument size properties of user-defined procedures,
|
|
<li>
|
|
term_pass2.m analyzes the termination properties of user-defined procedures.
|
|
<li>
|
|
term_traversal.m contains code common to the two passes.
|
|
<li>
|
|
term_errors.m defines the various kinds of termination errors
|
|
and prints the messages appropriate for each.
|
|
<li>
|
|
term_util.m defines the main types used in termination analysis
|
|
and contains utility predicates.
|
|
<li>
|
|
post_term_analysis.m contains error checking routines and optimizations
|
|
that depend upon the information obtained by termination analysis.
|
|
</ul>
|
|
|
|
<p>
|
|
|
|
Trail usage analysis. (trailing_analysis.m)
|
|
|
|
<ul>
|
|
<li>
|
|
This pass annotates each module with information about whether
|
|
the procedures in the module modify the trail or not. This
|
|
information can be used to avoid redundant trailing operations.
|
|
</ul>
|
|
|
|
<p>
|
|
|
|
Minimal model tabling analysis. (tabling_analysis.m)
|
|
|
|
<ul>
|
|
<li>
|
|
This pass annotates each goal in a module with information about
|
|
whether the goal calls procedures that are evaluated using
|
|
minimal model tabling. This information can be used to reduce
|
|
the overhead of minimal model tabling.
|
|
|
|
</ul>
|
|
|
|
<p>
|
|
|
|
Most of the remaining HLDS-to-HLDS transformations are optimizations:
|
|
|
|
<ul>
|
|
<li> specialization of higher-order and polymorphic predicates where the
|
|
value of the higher-order/type_info/typeclass_info arguments are known
|
|
(higher_order.m)
|
|
|
|
<li> attempt to introduce accumulators (accumulator.m). This optimizes
|
|
procedures whose tail consists of independent associative computations
|
|
or independent chains of commutative computations into a tail
|
|
recursive form by the introduction of accumulators. If lco is turned
|
|
on it can also transform some procedures so that only construction
|
|
unifications are after the recursive call. This pass must come before
|
|
lco, unused_args (eliminating arguments makes it hard to relate the
|
|
code back to the assertion) and inlining (can make the associative
|
|
call disappear).
|
|
<p>
|
|
This pass makes use of the goal_store.m module, which is a dictionary-like
|
|
data structure for storing HLDS goals.
|
|
|
|
<li> inlining (i.e. unfolding) of simple procedures (inlining.m)
|
|
|
|
<li> loop_inv.m: loop invariant hoisting. This transformation moves
|
|
computations within loops that are the same on every iteration to the outside
|
|
of the loop so that the invariant computations are only computed once. The
|
|
transformation turns a single looping predicate containing invariant
|
|
computations into two: one that computes the invariants on the first
|
|
iteration and then loops by calling the second predicate with extra arguments
|
|
for the invariant values. This pass should come after inlining, since
|
|
inlining can expose important opportunities for loop invariant hoisting.
|
|
Such opportunities might not be visible before inlining because only
|
|
*part* of the body of a called procedure is loop-invariant.
|
|
|
|
<li> deforestation and partial evaluation (deforest.m). This optimizes
|
|
multiple traversals of data structures within a conjunction, and
|
|
avoids creating intermediate data structures. It also performs
|
|
loop unrolling where the clause used is known at compile time.
|
|
deforest.m makes use of the following sub-modules (`pd_' stands for
|
|
"partial deduction"):
|
|
<ul>
|
|
<li> constraint.m transforms goals so that goals which can fail are
|
|
executed earlier.
|
|
<li> pd_cost.m contains some predicates to estimate the improvement
|
|
caused by deforest.m.
|
|
<li> pd_debug.m produces debugging output.
|
|
<li> pd_info.m contains a state type for deforestation.
|
|
<li> pd_term.m contains predicates to check that the deforestation
|
|
algorithm terminates.
|
|
<li> pd_util.m contains various utility predicates.
|
|
</ul>
|
|
|
|
<li> issue warnings about unused arguments from predicates, and create
|
|
specialized versions without them (unused_args.m); type_infos are often unused.
|
|
|
|
<li> delay_construct.m pushes construction unifications to the right in
|
|
semidet conjunctions, in an effort to reduce the probability that it will
|
|
need to be executed.
|
|
|
|
<li> unneeded_code.m looks for goals whose results are either not needed
|
|
at all, or needed in some branches of computation but not others. Provided
|
|
that the goal in question satisfies some requirements (e.g. it is pure,
|
|
it cannot fail etc), it either deletes the goal or moves it to the
|
|
computation branches where its output is needed.
|
|
|
|
<dt> lco.m finds predicates whose implementations would benefit
|
|
from last call optimization modulo constructor application.
|
|
|
|
<li> elimination of dead procedures (dead_proc_elim.m). Inlining, higher-order
|
|
specialization and the elimination of unused args can make procedures dead
|
|
even if the user doesn't, and automatically constructed unification and
|
|
comparison predicates are often dead as well.
|
|
|
|
<li> elimination of dead procedures (dead_proc_elim.m). Inlining, higher-order
|
|
specialization and the elimination of unused args can make procedures dead
|
|
even the user doesn't, and automatically constructed unification and
|
|
comparison predicates are often dead as well.
|
|
|
|
<li> tupling.m looks for predicates that pass around several arguments,
|
|
and modifies the code to pass around a single tuple of these arguments
|
|
instead if this looks like reducing the cost of parameter passing.
|
|
|
|
<li> untupling.m does the opposite of tupling.m: it replaces tuple arguments
|
|
with their components. This can be useful both for finding out how much
|
|
tupling has already been done manually in the source code, and to break up
|
|
manual tupling in favor of possibly more profitable automatic tupling.
|
|
|
|
<li> dep_par_conj.m transforms parallel conjunctions to add the wait and signal
|
|
operations required by dependent AND parallelism. To maximize the amount of
|
|
parallelism available, it tries to push the signals as early as possible
|
|
in producers and the waits as late as possible in the consumers, creating
|
|
specialized versions of predicates as needed.
|
|
|
|
<li> granularity.m tries to ensure that programs do not generate too much
|
|
parallelism. Its goal is to minimize parallelism's overhead while still
|
|
gaining all the parallelism the machine can actually exploit.
|
|
|
|
</ul>
|
|
|
|
<p>
|
|
|
|
The module transform.m contains stuff that is supposed to be useful
|
|
for high-level optimizations (but which is not yet used).
|
|
|
|
<p>
|
|
|
|
The last three HLDS-to-HLDS transformations implement
|
|
term size profiling (size_prof.m and complexity.m) and
|
|
deep profiling (deep_profiling.m, in the ll_backend.m package).
|
|
Both passes insert into procedure bodies, among other things,
|
|
calls to procedures (some of which are impure)
|
|
that record profiling information.
|
|
|
|
<hr>
|
|
<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
|
|
|
|
<h3> a. LLDS BACK-END </h3>
|
|
|
|
<p>
|
|
This is the ll_backend.m package.
|
|
|
|
<h4> 3a. LLDS-specific HLDS -> HLDS transformations </h4>
|
|
|
|
Before LLDS code generation, there are a few more passes which
|
|
annotate the HLDS with information used for LLDS code generation,
|
|
or perform LLDS-specific transformations on the HLDS:
|
|
|
|
<dl>
|
|
<dt> reducing the number of variables that have to be
|
|
saved across procedure calls (saved_vars.m)
|
|
<dd>
|
|
We do this by putting the code that generates
|
|
the value of a variable just before the use of
|
|
that variable, duplicating the variable and the
|
|
code that produces it if necessary, provided
|
|
the cost of doing so is smaller than the cost
|
|
of saving and restoring the variable would be.
|
|
|
|
<dt> transforming procedure definitions to reduce the number
|
|
of variables that need their own stack slots
|
|
(stack_opt.m)
|
|
<dd>
|
|
The main algorithm in stack_opt.m figures out when
|
|
variable A can be reached from a cell pointed to by
|
|
variable B, so that storing variable B on the stack
|
|
obviates the need to store variable A on the stack
|
|
as well.
|
|
This algorithm relies on an implementation of
|
|
the maximal matching algorithm in matching.m.
|
|
<dt> migration of builtins following branched structures
|
|
(follow_code.m)
|
|
<dd>
|
|
This transformation the results of follow_vars.m
|
|
(see below)
|
|
<dt> simplification again (simplify.m, in the check_hlds.m
|
|
package)
|
|
<dd>
|
|
We run this pass a second time in case the intervening
|
|
transformations have created new opportunities for
|
|
simplification. It needs to be run immediately
|
|
before code generation, because it enforces some
|
|
invariants that the LLDS code generator relies on.
|
|
<dt> annotation of goals with liveness information (liveness.m)
|
|
<dd>
|
|
This records the birth and death of each variable
|
|
in the HLDS goal_info.
|
|
<dt> allocation of stack slots
|
|
<dd>
|
|
This is done by stack_alloc.m, with the assistance of
|
|
the following modules:
|
|
|
|
<ul>
|
|
<li> live_vars.m works out which variables need
|
|
to be saved on the stack when.
|
|
|
|
<li> graph_colour.m (in the libs.m package)
|
|
contains the algorithm that
|
|
stack_alloc.m calls to convert sets of variables
|
|
that must be saved on the stack at the same time
|
|
to an assignment of a stack slot to each such variable.
|
|
</ul>
|
|
<dt> allocating the follow vars (follow_vars.m)
|
|
<dd>
|
|
Traverses backwards over the HLDS, annotating some
|
|
goals with information about what locations variables
|
|
will be needed in next. This allows us to generate
|
|
more efficient code by putting variables in the right
|
|
spot directly. This module is not called from
|
|
mercury_compile.m; it is called from store_alloc.m.
|
|
<dt> allocating the store map (store_alloc.m)
|
|
<dd>
|
|
Annotates each branched goal with variable location
|
|
information so that we can generate correct code
|
|
by putting variables in the same spot at the end
|
|
of each branch.
|
|
<dt> computing goal paths (goal_path.m
|
|
in the check_hlds.m package)
|
|
<dd>
|
|
The goal path of a goal defines its position in
|
|
the procedure body. This transformation attaches
|
|
its goal path to every goal, for use by the debugger.
|
|
</dl>
|
|
|
|
<h4> 4a. Code generation. </h4>
|
|
<dl>
|
|
<dt> code generation
|
|
|
|
<dd>
|
|
Code generation converts HLDS into LLDS.
|
|
For the LLDS back-end, this is also the point at which we
|
|
insert code to handle debugging and trailing, and to do
|
|
heap reclamation on failure.
|
|
The top level code generation module is proc_gen.m,
|
|
which looks after the generation of code for procedures
|
|
(including prologues and epilogues).
|
|
The predicate for generating code for arbitrary goals is in code_gen.m,
|
|
but that module handles only sequential conjunctions; it calls
|
|
other modules to handle other kinds of goals:
|
|
|
|
<ul>
|
|
<li> ite_gen.m (if-then-elses)
|
|
<li> call_gen.m (predicate calls and also calls to
|
|
out-of-line unification procedures)
|
|
<li> disj_gen.m (disjunctions)
|
|
<li> par_conj_gen.m (parallel conjunctions)
|
|
<li> unify_gen.m (unifications)
|
|
<li> switch_gen.m (switches), which has sub-modules
|
|
<ul>
|
|
<li> dense_switch.m
|
|
<li> lookup_switch.m
|
|
<li> string_switch.m
|
|
<li> tag_switch.m
|
|
<li> switch_case.m
|
|
<li> switch_util.m -- this is in the backend_libs.m
|
|
package, since it is also used by MLDS back-end
|
|
</ul>
|
|
<li> commit_gen.m (commits)
|
|
<li> pragma_c_gen.m (embedded C code)
|
|
</ul>
|
|
|
|
<p>
|
|
|
|
The code generator also calls middle_rec.m to do middle recursion
|
|
optimization, which is implemented during code generation.
|
|
|
|
<p>
|
|
|
|
The code generation modules make use of
|
|
<dl>
|
|
<dt> code_info.m
|
|
<dd>
|
|
The main data structure for the code generator.
|
|
<dt> var_locn.m
|
|
<dd>
|
|
This defines the var_locn type, which is a
|
|
sub-component of the code_info data structure;
|
|
it keeps track of the values and locations of variables.
|
|
It implements eager code generation.
|
|
<dt> exprn_aux.m
|
|
<dd>
|
|
Various utility predicates.
|
|
<dt> code_util.m
|
|
<dd>
|
|
Some miscellaneous preds used for code generation.
|
|
<dt> lookup_util.m
|
|
<dd>
|
|
Some miscellaneous preds used for lookup switch
|
|
(and lookup disjunction) generation.
|
|
<dt> continuation_info.m
|
|
<dd>
|
|
For accurate garbage collection, collects
|
|
information about each live value after calls,
|
|
and saves information about procedures.
|
|
<dt> trace_gen.m
|
|
<dd>
|
|
Inserts calls to the runtime debugger.
|
|
<dt> trace_params.m (in the libs.m package, since it
|
|
is considered part of option handling)
|
|
<dd>
|
|
Holds the parameter settings controlling
|
|
the handling of execution tracing.
|
|
</dl>
|
|
|
|
<dt> code generation for `pragma export' declarations (export.m)
|
|
<dd> This is handled separately from the other parts of code generation.
|
|
mercury_compile.m calls the procedures `export.produce_header_file'
|
|
and `export.get_pragma_exported_procs' to produce C code fragments
|
|
which declare/define the C functions which are the interface stubs
|
|
for procedures exported to C.
|
|
|
|
<dt> generation of constants for RTTI data structures
|
|
<dd> This could also be considered a part of code generation,
|
|
but for the LLDS back-end this is currently done as part
|
|
of the output phase (see below).
|
|
|
|
</dl>
|
|
|
|
<p>
|
|
|
|
The result of code generation is the Low Level Data Structure (llds.m),
|
|
which may also contains some data structures whose types are defined in rtti.m.
|
|
The code for each procedure is generated as a tree of code fragments
|
|
which is then flattened (tree.m).
|
|
|
|
|
|
<h4> 5a. Low-level optimization (LLDS). </h4>
|
|
|
|
<p>
|
|
|
|
Most of the various LLDS-to-LLDS optimizations are invoked from optimize.m.
|
|
They are:
|
|
|
|
<ul>
|
|
<li> optimization of jumps to jumps (jumpopt.m)
|
|
|
|
<li> elimination of duplicate code sequences within procedures (dupelim.m)
|
|
|
|
<li> elimination of duplicate procedure bodies (dupproc.m,
|
|
invoked directly from mercury_compile.m)
|
|
|
|
<li> optimization of stack frame allocation/deallocation (frameopt.m)
|
|
|
|
<li> filling branch delay slots (delay_slot.m)
|
|
|
|
<li> dead code and dead label removal (labelopt.m)
|
|
|
|
<li> peephole optimization (peephole.m)
|
|
|
|
<li> introduction of local C variables (use_local_vars.m)
|
|
|
|
<li> removal of redundant assignments, i.e. assignments that assign a value
|
|
that the target location already holds (reassign.m)
|
|
|
|
</ul>
|
|
|
|
In addition, stdlabel.m performs standardization of labels.
|
|
This is not an optimization itself,
|
|
but it allows other optimizations to be evaluated more easily.
|
|
|
|
<p>
|
|
|
|
The module opt_debug.m contains utility routines used for debugging
|
|
these LLDS-to-LLDS optimizations.
|
|
|
|
<p>
|
|
|
|
Several of these optimizations (frameopt and use_local_vars) also
|
|
use livemap.m, a module that finds the set of locations live at each label.
|
|
|
|
<p>
|
|
|
|
Use_local_vars numbering also introduces
|
|
references to temporary variables in extended basic blocks
|
|
in the LLDS representation of the C code.
|
|
The transformation to insert the block scopes
|
|
and declare the temporary variables is performed by wrap_blocks.m.
|
|
|
|
<p>
|
|
|
|
Depending on which optimization flags are enabled,
|
|
optimize.m may invoke many of these passes multiple times.
|
|
|
|
<p>
|
|
|
|
Some of the low-level optimization passes use basic_block.m,
|
|
which defines predicates for converting sequences of instructions to
|
|
basic block format and back, as well as opt_util.m, which contains
|
|
miscellaneous predicates for LLDS-to-LLDS optimization.
|
|
|
|
|
|
<h4> 6a. Output C code </h4>
|
|
|
|
<ul>
|
|
<li> type_ctor_info.m
|
|
(in the backend_libs.m package, since it is shared with the MLDS back-end)
|
|
generates the type_ctor_gen_info structures that list
|
|
items of information (including unification, index and compare predicates)
|
|
associated with each declared type constructor that go into the static
|
|
type_ctor_info data structure. If the type_ctor_gen_info structure is not
|
|
eliminated as inaccessible, this module adds the corresponding type_ctor_info
|
|
structure to the RTTI data structures defined in rtti.m,
|
|
which are part of the LLDS.
|
|
|
|
<li> base_typeclass_info.m
|
|
(in the backend_libs.m package, since it is shared with the MLDS back-end)
|
|
generates the base_typeclass_info structures that
|
|
list the methods of a class for each instance declaration. These are added to
|
|
the RTTI data structures, which are part of the LLDS.
|
|
|
|
<li> stack_layout.m generates the stack_layout structures for
|
|
accurate garbage collection. Tables are created from the data
|
|
collected in continuation_info.m.
|
|
|
|
Stack_layout.m uses prog_rep.m to generate bytecode representations
|
|
of procedure bodies for use by the declarative debugger.
|
|
|
|
<li> Type_ctor_info structures and stack_layout structures both contain
|
|
pseudo_type_infos, which are type_infos with holes for type variables;
|
|
these are generated by pseudo_type_info.m
|
|
(in the backend_libs.m package, since it is shared with the MLDS back-end).
|
|
|
|
<li> llds_common.m extracts static terms from the main body of the LLDS, and
|
|
puts them at the front. If a static term originally appeared several times,
|
|
it will now appear as a single static term with multiple references to it.
|
|
[XXX FIXME this module has now been replaced by global_data.m]
|
|
|
|
<li> transform_llds.m is responsible for doing any source to source
|
|
transformations on the llds which are required to make the C output
|
|
acceptable to various C compilers. Currently computed gotos can have
|
|
their maximum size limited to avoid a fixed limit in lcc.
|
|
|
|
<li> Final generation of C code is done in llds_out.m, which subcontracts the
|
|
output of RTTI structures to rtti_out.m and of other static
|
|
compiler-generated data structures (such as those used by the debugger,
|
|
the deep profiler, and in the future by the garbage collector)
|
|
to layout_out.m.
|
|
</ul>
|
|
|
|
|
|
<hr>
|
|
<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
|
|
|
|
<h3> b. MLDS BACK-END </h3>
|
|
|
|
<p>
|
|
|
|
This is the ml_backend.m package.
|
|
|
|
<p>
|
|
|
|
The original LLDS code generator generates very low-level code,
|
|
since the LLDS was designed to map easily to RISC architectures.
|
|
We have developed a new back-end that generates much higher-level
|
|
code, suitable for generating Java, high-level C, etc.
|
|
This back-end uses the Medium Level Data Structure (mlds.m) as its
|
|
intermediate representation.
|
|
|
|
<h4> 3b. pre-passes to annotate/transform the HLDS </h4>
|
|
|
|
<p>
|
|
Before code generation there is a pass which annotates the HLDS with
|
|
information used for code generation:
|
|
|
|
<ul>
|
|
<li> mark_static_terms.m marks construction unifications
|
|
which can be implemented using static constants rather
|
|
than heap allocation.
|
|
</ul>
|
|
|
|
<p>
|
|
For the MLDS back-end, we've tried to keep the code generator simple.
|
|
So we prefer to do things as HLDS to HLDS transformations where possible,
|
|
rather than complicating the HLDS to MLDS code generator.
|
|
Thus we have a pass which transforms the HLDS to handle trailing:
|
|
|
|
<ul>
|
|
<li> add_trail_ops.m inserts code to manipulate the trail,
|
|
in particular ensuring that we apply the appropriate
|
|
trail operations before each choice point, when execution
|
|
resumes after backtracking, and whenever we do a commit.
|
|
The trail operations are represented as (and implemented as)
|
|
calls to impure procedures defined in library/private_builtin.m.
|
|
<li> add_heap_ops.m is very similar to add_trail_ops.m;
|
|
it inserts code to do heap reclamation on backtracking.
|
|
</ul>
|
|
|
|
<h4> 4b. MLDS code generation </h4>
|
|
<ul>
|
|
<li> ml_code_gen.m converts HLDS code to MLDS.
|
|
The following sub-modules are used to handle different constructs:
|
|
<ul>
|
|
<li> ml_unify_gen.m
|
|
<li> ml_closure_gen.m
|
|
<li> ml_call_gen.m
|
|
<li> ml_switch_gen.m, which in turn has sub-modules
|
|
<ul>
|
|
<li> ml_dense_switch.m
|
|
<li> ml_string_switch.m
|
|
<li> ml_tag_switch.m
|
|
<li> switch_util.m (in the backend_libs.m package,
|
|
since it is also used by LLDS back-end)
|
|
</ul>
|
|
</ul>
|
|
The module ml_code_util.m provides utility routines for
|
|
MLDS code generation. The module ml_util.m provides some
|
|
general utility routines for the MLDS.
|
|
<li> ml_type_gen.m converts HLDS types to MLDS.
|
|
<li> type_ctor_info.m and base_typeclass_info.m generate
|
|
the RTTI data structures defined in rtti.m and pseudo_type_info.m
|
|
(those four modules are in the backend_libs.m package, since they
|
|
are shared with the LLDS back-end)
|
|
and then rtti_to_mlds.m converts these to MLDS.
|
|
</ul>
|
|
|
|
<h4> 5b. MLDS transformations </h4>
|
|
<ul>
|
|
<li> ml_tailcall.m annotates the MLDS with information about tailcalls.
|
|
It also has a pass to implement the `--warn-non-tail-recursion' option.
|
|
<li> ml_optimize.m does MLDS->MLDS optimizations
|
|
<li> ml_elim_nested.m does two MLDS transformations that happen
|
|
to have a lot in common: (1) eliminating nested functions
|
|
and (2) adding code to handle accurate garbage collection.
|
|
</ul>
|
|
|
|
<h4> 6b. MLDS output </h4>
|
|
|
|
<p>
|
|
There are currently four backends that generate code from MLDS:
|
|
one generates C/C++ code,
|
|
one generates assembler (by interfacing with the GCC back-end),
|
|
one generates Microsoft's Intermediate Language (MSIL or IL),
|
|
and one generates Java.
|
|
|
|
<ul>
|
|
<li>mlds_to_c.m converts MLDS to C/C++ code.
|
|
</ul>
|
|
|
|
<p>
|
|
|
|
The MLDS->asm backend is logically part of the MLDS back-ends,
|
|
but it is in a module of its own (mlds_to_gcc.m), rather than being
|
|
part of the ml_backend package, so that we can distribute a version
|
|
of the Mercury compiler which does not include it. There is a wrapper
|
|
module called maybe_mlds_to_gcc.m which is generated at configuration time
|
|
so that mlds_to_gcc.m will be linked in iff the GCC back-end is available.
|
|
|
|
<p>
|
|
|
|
The MLDS->IL backend is broken into several submodules.
|
|
<ul>
|
|
<li> mlds_to_ilasm.m converts MLDS to IL assembler and writes it to a .il file.
|
|
<li> mlds_to_il.m converts MLDS to IL
|
|
<li> ilds.m contains representations of IL
|
|
<li> ilasm.m contains output routines for writing IL to assembler.
|
|
<li> il_peephole.m performs peephole optimization on IL instructions.
|
|
</ul>
|
|
After IL assembler has been emitted, ILASM in invoked to turn the .il
|
|
file into a .dll or .exe.
|
|
|
|
<p>
|
|
|
|
The MLDS->Java backend is broken into two submodules.
|
|
<ul>
|
|
<li> mlds_to_java.m converts MLDS to Java and writes it to a .java file.
|
|
<li> java_util.m contains some utility routines.
|
|
</ul>
|
|
After the Java code has been emitted, a Java compiler (normally javac)
|
|
is invoked to turn the .java file into a .class file containing Java bytecodes.
|
|
|
|
<hr>
|
|
<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
|
|
|
|
<h3> c. BYTECODE BACK-END </h3>
|
|
|
|
<p>
|
|
This is the bytecode_backend.m package.
|
|
|
|
<p>
|
|
|
|
The Mercury compiler can translate Mercury programs into bytecode for
|
|
interpretation by a bytecode interpreter. The intent of this is to
|
|
achieve faster turn-around time during development. However, the
|
|
bytecode interpreter has not yet been written.
|
|
|
|
<ul>
|
|
<li> bytecode.m defines the internal representation of bytecodes, and contains
|
|
the predicates to emit them in two forms. The raw bytecode form is emitted
|
|
into <filename>.bytecode for interpretation, while a human-readable
|
|
form is emitted into <filename>.bytedebug for visual inspection.
|
|
|
|
<li> bytecode_gen.m contains the predicates that translate HLDS into bytecode.
|
|
|
|
<li> bytecode_data.m contains the predicates that translate ints, strings
|
|
and floats into bytecode.
|
|
</ul>
|
|
|
|
<hr>
|
|
<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
|
|
|
|
<h3> d. ERLANG BACK-END </h3>
|
|
|
|
<p>
|
|
This is the erl_backend.m package.
|
|
|
|
<p>
|
|
|
|
The Mercury compiler can translate Mercury programs into Erlang.
|
|
The intent of this is to take advantage of the features of the
|
|
Erlang implementation (concurrency, fault tolerance, etc.)
|
|
However, the backend is still incomplete.
|
|
This back-end uses the Erlang Data Structure (elds.m) as its
|
|
intermediate representation.
|
|
|
|
<h4> 4d. ELDS code generation </h4>
|
|
<ul>
|
|
<li> erl_code_gen.m converts HLDS code to ELDS.
|
|
The following sub-modules are used to handle different constructs:
|
|
<ul>
|
|
<li> erl_unify_gen.m
|
|
<li> erl_call_gen.m
|
|
</ul>
|
|
The module erl_code_util.m provides utility routines for
|
|
ELDS code generation.
|
|
<li> erl_rtti.m converts RTTI data structures defined in rtti.m into
|
|
ELDS functions which return the same information when called.
|
|
</ul>
|
|
|
|
<h4> 6d. ELDS output </h4>
|
|
|
|
<ul>
|
|
<li>elds_to_erlang.m converts ELDS to Erlang code.
|
|
</ul>
|
|
|
|
<hr>
|
|
<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
|
|
|
|
<h3> SMART RECOMPILATION </h3>
|
|
|
|
<p>
|
|
This is the recompilation.m package.
|
|
|
|
<p>
|
|
|
|
The Mercury compiler can record program dependency information
|
|
to avoid unnecessary recompilations when an imported module's
|
|
interface changes in a way which does not invalidate previously
|
|
compiled code.
|
|
|
|
<ul>
|
|
<li> recompilation.m contains types used by the other smart
|
|
recompilation modules.
|
|
|
|
<li> recompilation_version.m generates version numbers for program items
|
|
in interface files.
|
|
|
|
<li> recompilation_usage.m works out which program items were used
|
|
during a compilation.
|
|
|
|
<li> recompilation_check.m is called before recompiling a module.
|
|
It uses the information written by recompilation_version.m and
|
|
recompilation_usage.m to work out whether the recompilation is
|
|
actually needed.
|
|
</ul>
|
|
|
|
<hr>
|
|
<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
|
|
|
|
<h3> MISCELLANEOUS </h3>
|
|
|
|
|
|
The modules special_pred.m (in the hlds.m package) and unify_proc.m
|
|
(in the check_hlds.m package) contain stuff for handling the special
|
|
compiler-generated predicates which are generated for
|
|
each type: unify/2, compare/3, and index/1 (used in the
|
|
implementation of compare/3).
|
|
|
|
<p>
|
|
This module is part of the transform_hlds.m package.
|
|
|
|
<dl>
|
|
<dt> dependency_graph.m:
|
|
<dd>
|
|
This contains predicates to compute the call graph for a
|
|
module, and to print it out to a file.
|
|
(The call graph file is used by the profiler.)
|
|
The call graph may eventually also be used by det_analysis.m,
|
|
inlining.m, and other parts of the compiler which could benefit
|
|
from traversing the predicates in a module in a bottom-up or
|
|
top-down fashion with respect to the call graph.
|
|
</dl>
|
|
|
|
<p>
|
|
The following modules are part of the backend_libs.m package.
|
|
|
|
<dl>
|
|
<dt> builtin_ops:
|
|
<dd>
|
|
This module defines the types unary_op and binary_op
|
|
which are used by several of the different back-ends:
|
|
bytecode.m, llds.m, and mlds.m.
|
|
|
|
<dt> c_util:
|
|
<dd>
|
|
This module defines utility routines useful for generating
|
|
C code. It is used by both llds_out.m and mlds_to_c.m.
|
|
|
|
<dt> name_mangle:
|
|
<dd>
|
|
This module defines utility routines useful for mangling
|
|
names to forms acceptable as identifiers in target languages.
|
|
|
|
<dt> compile_target_code.m
|
|
<dd>
|
|
Invoke C, C#, IL, Java, etc. compilers and linkers to compile
|
|
and link the generated code.
|
|
|
|
</dl>
|
|
|
|
<p>
|
|
The following modules are part of the libs.m package.
|
|
|
|
<dl>
|
|
|
|
<dt> process_util.m:
|
|
<dd>
|
|
Predicates to deal with process creation and signal handling.
|
|
This module is mainly used by make.m and its sub-modules.
|
|
|
|
<dt> timestamp.m
|
|
<dd>
|
|
Contains an ADT representing timestamps used by smart
|
|
recompilation and `mmc --make'.
|
|
|
|
<dt> graph_color.m
|
|
<dd>
|
|
Graph colouring. <br>
|
|
This is used by the LLDS back-end for register allocation
|
|
|
|
<dt> tree.m
|
|
<dd>
|
|
A simple tree data type. <br>
|
|
Used by the LLDS, and IL back-ends for collecting
|
|
together the different fragments of the generated code.
|
|
|
|
<dt> lp.m
|
|
<dd>
|
|
Implements the linear programming algorithm for optimizing
|
|
a set of linear constraints with respect to a linear
|
|
cost function. This is used by termination analyser.
|
|
|
|
<dt> lp_rational.m
|
|
<dd>
|
|
Implements the linear programming algorithm for optimizing
|
|
a set of linear constraints with respect to a linear
|
|
cost function, for rational numbers.
|
|
This is used by termination analyser.
|
|
|
|
<dt> rat.m
|
|
<dd>
|
|
Implements rational numbers.
|
|
|
|
<dt> compiler_util.m:
|
|
<dd>
|
|
Generic utility predicates, mainly for error handling.
|
|
</dl>
|
|
|
|
<hr>
|
|
<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
|
|
|
|
<h3> CURRENTLY UNDOCUMENTED </h3>
|
|
|
|
<ul>
|
|
<li> mmc_analysis.m
|
|
</ul>
|
|
|
|
<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
|
|
|
|
<h3> CURRENTLY USELESS </h3>
|
|
|
|
<dl>
|
|
<dt> atsort.m (in the libs.m package)
|
|
<dd>
|
|
Approximate topological sort.
|
|
This was once used for traversing the call graph,
|
|
but nowadays we use relation.atsort from library/relation.m.
|
|
|
|
</dl>
|
|
|
|
<hr>
|
|
<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
|
|
|
|
Last update was $Date: 2007-12-30 08:24:22 $ by $Author: zs $@cs.mu.oz.au. <br>
|
|
</body>
|
|
</html>
|