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b4813457c9
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A rewrite of termination analysis to make it significantly easier to modify,
and to extend its capabilities.
compiler/error_util.m:
A new file containing code that makes it easier to generate
nicely formatted error messages.
compiler/termination.m:
Updates to reflect the changes to the representation of termination
information.
Instead of doing pass 1 on all SCCs and then pass 2 on all SCCs,
we now do both pass 1 and 2 on an SCC before moving on to the next.
Do not insist that either all procedures in an SCC are
compiler-generated or all are user-written, since this need not be
true in the presence of user-defined equality predicates.
Clarify the structure of the code that handles builtins and compiler
generated predicates.
Concentrate all the code for updating module_infos in this module.
Previously it was scattered in several places in several files.
Put all the code for writing out termination information at the
end of the module in a logical order.
compiler/term_traversal.m:
A new file containing code used by both pass 1 and pass 2 to
traverse procedure bodies.
compiler/term_pass1.m:
Use the new traversal module.
Clarify the fixpoint computation on the set of output supplier
arguments.
Remove duplicates from the list of equations given to the solver.
This avoids a det stack overflow in lp.m when doing termination
analysis on options.m.
If an output argument of a predicate makes sense only in the absence
of errors, then return it only in the absence of errors.
compiler/term_pass2.m:
Use the new traversal module. Unlike the previous code, this allows us
to ignore recursive calls with input arguments bigger than the head
if those calls occur after goals that cannot succeed (since those
calls will never be reached).
Implement a better way of doing single argument analysis, which
(unlike the previous version) works in the presence of mutual recursion
and other calls between the recursive call and the start of the clause.
Implement a more precise way of checking for recursions that don't
cause termination problems. We now allow calls from p to q in which
the recursive input supplier arguments can grow, provided that on
any path on which q can call p, directly or indirectly, the recursive
input supplier arguments shrink by a greater amount.
If an output argument of a predicate makes sense only in the absence
of errors, then return it only in the absence of errors.
compiler/term_util.m:
Updates to reflect the changes to the representation of termination
information.
Reorder to put related code together.
Change the interface of several predicates to better reflect the
way they are used.
Add some more utility predicates.
compiler/term_errors.m:
Small changes to the set of possible errors, and major changes in
the way the messages are printed out (we now use error_util).
compiler/options.m:
Change --term-single-arg from being a bool to an int option,
whose value indicates the maximum size of an SCC in which we try
single argument analysis. (Large SCCs can cause single-arg analysis
to require a lot of iterations.)
Add an (int) option that controls the max number of paths
that we are willing to analyze (analyzing too many paths can cause
det stack overflow).
Add an (int) option that controls the max number of causes of
nontermination that we print out.
compiler/hlds_pred.m:
Use two separate slots in the proc_info to hold argument size data
and termination info, instead of the single slot used until now.
The two kinds of information are produced and used separately.
Make the layout of the get and set procedures for proc_infos more
regular, to facilitate later updates.
The procedures proc_info_{,set_}variables did the same work as
proc_info_{,set_}varset. To eliminate potential confusion, I
removed the first set.
compiler/*.m:
Change proc_info_{,set_}variables to proc_info_{,set_}varset.
compiler/hlds_out.m:
compiler/make_hlds.m:
compiler/mercury_to_mercury.m:
Change the code to handle the arg size data and the termination
info separately.
compiler/prog_data.m:
Change the internal representation of termination_info pragmas to
hold the arg size data and the termination info separately.
compiler/prog_io_pragma.m:
Change the external representation of termination_info pragmas to
group the arg size data together with the output supplier data,
to which it is logically connected.
compiler/module_qual.m:
compiler/modules.m:
Change the code to accommodate the change to the internal
representation of termination_info pragmas.
compiler/notes/compiler_design.html:
Fix some documentation rot, and clarify some points.
Document termination analysis.
doc/user_guide.texi:
Document --term-single-arg and the new options.
Remove spaces from the ends of lines.
library/bag.m:
Add a new predicate, bag__least_upper_bound.
Fix code that would do the wrong thing if executed by Prolog.
Remove spaces from the ends of lines.
library/list.m:
Add a new predicate, list__take_upto.
library/set{,_ordlist}.m:
Add a new predicate, set{,_ordlist}__count.
tests/term/*:
A bunch of new test cases to test the behaviour of termination
analysis. They are the small benchmark suite from our paper.
tests/Mmakefile:
Enable the new test case directory.
797 lines
26 KiB
HTML
797 lines
26 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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This file contains various notes about the design of the compiler.
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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 (Goedel,
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the bytecode of a debugger currently under development, and in the future
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the Aditi Relational Language).
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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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The basic design is that compilation is broken into the following
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stages:
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<ol>
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<li> parsing (source files -> HLDS)
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<li> semantic analysis and error checking (HLDS -> annotated HLDS)
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<li> high-level transformations (annotated HLDS -> annotated HLDS)
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<li> code generation (annotated HLDS -> LLDS)
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<li> low-level optimizations (LLDS -> LLDS)
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<li> output C code (LLDS -> C)
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</ol>
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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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<hr>
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<!-------------------------->
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<h2> DETAILED DESIGN </h2> (well, more detailed than the OUTLINE anyway ;-)
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<p>
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The action is co-ordinated from mercury_compile.m.
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<p>
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<h3> 0. Option handling </h3>
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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> 1. Parsing </h3>
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<p>
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<ul>
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<li> lexical analysis (library/lexer.m)
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<li> stage 1 parsing - convert strings to terms. <br>
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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> stage 2 parsing - convert terms to `items' (declarations, clauses, etc.)
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<br>
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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
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definition is in prog_data.m, while the code to create it is in
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prog_io.m and its submodules prog_io_dcg.m (which handles clauses
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using Definite Clause Grammar notation), prog_io_goal.m (which handles
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goals), prog_io_pragma.m (which handles pragma declarations),
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prog_io_typeclass.m (which handles typeclass and instance declarations)
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and prog_io_util.m (which defines predicates and types needed by the
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other prog_io*.m modules. The data structure for insts is stored in
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its own module, inst.m.
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<p>
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The modules prog_out.m and mercury_to_mercury.m contain predicates
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for printing the parse tree. prog_util.m contains some utility
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predicates for manipulating the parse tree.
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<li> imports and exports are handled at this point (modules.m) <br>
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modules.m has the code to write out `.int', `.int2', `.int3',
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`.d' and `.dep' files.
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<li> module qualification of types, insts and modes <br>
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module_qual.m - <br>
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Adds module qualifiers to all types insts and modes,
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checking that a given type, inst or mode exists and that
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there is only possible match. This is done here because
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it must be done before the `.int' and `.int2' interface files
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are written. This also checks whether imports are really needed
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in the interface.
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<br>
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Notes on module qualification:
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<ul>
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<li> all types, typeclasses, insts and modes occuring in pred, func,
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type, typeclass and mode declarations are module qualified by
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module_qual.m.
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<li> all types, insts and modes occuring in lambda expressions and
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explicit type qualifications are module qualified in
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make_hlds.m.
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<li> constructors occuring in predicate and function mode declarations
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are module qualified during type checking.
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<li> predicate and function calls and constructors within goals
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are module qualified during mode analysis.
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<li> predicate and function names in typeclass instance declarations
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are qualified in check_typeclass.m (after mode analysis).
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</ul>
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<li> reading and writing of optimization interfaces (intermod.m). <br>
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<module>.opt contains clauses for exported preds suitable for
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inlining or higher-order specialization. The .opt file for the
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current module is written after type-checking. .opt files
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for imported modules are read here.
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<li> expansion of equivalence types (equiv_type.m) <br>
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This is really part of type-checking, but is done
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on the item_list rather than on the HLDS because it
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turned out to be much easier to implement that way.
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<li> conversion to superhomogeneous form and into HLDS <br>
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make_hlds.m transforms the code into superhomogeneous form,
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and at the same time converts the parse tree into the HLDS.
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make_hlds.m also calls make_tags.m which chooses the data
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representation for each discriminated union type by
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assigning tags to each functor.
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</ul>
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<p>
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The result at this stage is the High Level Data Structure,
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which is defined in four files:
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<ol>
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<li> hlds_data.m defines the parts of the HLDS concerned with
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function symbols, types, insts, modes and determinisms;
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<li> hlds_goal.m defines the part of the HLDS concerned with the
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structure of goals, including the annotations on goals;
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<li> hlds_pred.m defines the part of the HLDS concerning
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predicates and procedures;
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<li> hlds_module.m defines the top-level parts of the HLDS,
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including the type module_info.
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</ol>
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The module hlds_out.m contains predicates to dump the HLDS to a file.
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The module goal_util.m contains predicates for renaming variables
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in an HLDS goal.
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<p>
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<h3> 2. Semantic analysis and error checking </h3>
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<p>
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<dl>
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<dt> implicit quantification
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<dd>
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quantification.m handles implicit quantification and computes
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the set of non-local variables for each sub-goal
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<dt> type checking
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<dd>
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<ul>
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<li> typecheck.m handles type checking, overloading resolution &
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module name resolution, and almost fully qualifies all predicate
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and functor names. It sets the map(var, type) field in the
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pred_info. However, typecheck.m doesn't figure out the pred_id
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for function calls or calls to overloaded predicates; that can't
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be done in a single pass of typechecking, and so it is done
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later on in modes.m. Typeclass constraints are checked here, and
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any redundant constraints that are eliminated are recorded (as
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constraint_proofs) in the pred_info for future reference. When it has
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finished, typecheck.m calls clause_to_proc.m to make duplicate copies
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of the clauses for each different mode of a predicate; all later
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stages work on procedures, not predicates.
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<li> type_util.m contains utility predicates dealing with types
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that are used in a variety of different places within the compiler
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</ul>
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<dt> purity analysis
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<dd>
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purity.m is responsible for purity checking, as well as
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defining the <CODE>purity</CODE> type and a few public
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operations on it. It also completes the handling of predicate
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overloading for cases which typecheck.m is unable to handle.
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<dt> mode analysis
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<dd>
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<ul>
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<li> modes.m is the main mode analysis module.
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It checks that the code is mode-correct, reordering it
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if necessary, and annotates each goal with a delta-instmap
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that specifies the changes in instantiatedness of each
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variable over that goal.
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<li> modecheck_unify.m is the sub-module which analyses
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unification goals. It also converts higher-order pred terms
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into lambda expressions and module qualifies data constructors.
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<li> modecheck_call.m is the sub-module which analyses calls.
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It also converts function calls into predicate calls.
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<p>
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The following sub-modules are used:
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<dl>
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<dt> mode_info.m
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<dd>
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(the main data structure for mode analysis)
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<dt> delay_info.m
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<dd>
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(a sub-component of the mode_info data
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structure used for storing the information
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for scheduling: which goals are currently
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delayed, what variables they are delayed on, etc.)
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<dt> instmap.m
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<dd>
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Defines the instmap and instmap_delta ADTs
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which store information on what instantiations
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a set of variables may be bound to.
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<dt> inst_match.m
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<dd>
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This contains the code for examining insts and
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checking whether they match.
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<dt> inst_util.m
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<dd>
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This contains the code for creating new insts from
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old ones: unifying them, merging them and so on.
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<dt> mode_errors.m
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<dd>
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This module contains all the code to
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print error messages for mode errors
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</dl>
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<li> mode_util.m contains miscellaneous useful predicates dealing
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with modes (many of these are used by lots of later stages
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of the compiler)
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<li> mode_debug.m contains utility code for tracing the actions
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of the mode checker.
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</ul>
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<dt> indexing and determinism analysis
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<dd>
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<ul>
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<li> switch_detection.m transforms into switches those disjunctions
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in which several disjuncts test the same variable against different
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function symbols.
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<li> cse_detection.m looks for disjunctions in which each disjunct tests
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the same variable against the same function symbols, and hoists any
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such unifications out of the disjunction.
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If cse_detection.m modifies the code,
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it will re-run mode analysis and switch detection.
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<li> det_analysis.m annotates each goal with its determinism;
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it inserts cuts in the form of "some" goals wherever the determinisms
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and delta instantiations of the goals involved make it necessary.
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Any errors found during determinism analysis are reported by
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det_report.m.
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Det_util.m contains utility predicates used in several modules.
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</ul>
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<dt> checking of unique modes (unique_modes.m)
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<dd>
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unique_modes.m checks that non-backtrackable unique modes were
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not used in a context which might require backtracking.
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Note that what unique_modes.m does is quite similar to
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what modes.m does, and unique_modes calls lots of predicates
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defined in modes.m to do it.
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<dt> checking typeclass instances (check_typeclass.m)
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<dd>
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check_typeclass.m checks that, each instance declaration, that the
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types, modes and determinism of each predicate/function that is a
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method of the class is correct (ie. that it matches the typeclass
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declaration). In this pass, pred_ids and proc_ids are assigned to
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the methods for each instance. In addition, while checking that the
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superclasses of a class are satisfied by the instance declaration, a
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set of constraint_proofs are built up for the superclass constraints.
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These are used by polymorphism.m when generating the
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base_typeclass_info for the instance.
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<dt> simplification (simplify.m)
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<dd>
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simplify.m finds and exploits opportunities for simplifying the
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internal form of the program, both to optimize the code and to
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massage the code into a form the code generator will accept.
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It also warns the programmer about any constructs that are so simple
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that they should not have been included in the program in the first
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place.
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simplify.m calls common.m which looks for (a) construction unifications
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that construct a term that is the same as one that already exists,
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or (b) repeated calls to a predicate with the same inputs, and replaces
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them with assignment unifications.
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simplify.m also attempts to partially evaluate calls to builtin
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procedures if the inputs are all constants (see const_prop.m).
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</dl>
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<h3> 3. High-level transformations </h3>
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<p>
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The first two passes of this stage are code simplifications.
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<ul>
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<li> introduction of type_info arguments for polymorphic predicates,
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introduction of typeclass_info arguments for typeclass-constrained predicates
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and transformation of complicated unifications into predicate calls
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(polymorphism.m)
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<li> removal of lambda expressions (lambda.m) <br>
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<p>
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lambda.m converts lambda expressions into higher-order predicate
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terms referring to freshly introduced separate predicates.
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This pass needs to come after unique_modes.m to ensure that
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the modes we give to the introduced predicates are correct.
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It also needs to come after polymorphism.m since polymorphism.m
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doesn't handle higher-order predicate constants.
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</ul>
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<p>
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To improve efficiency, the above two passes are actually combined into
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one - polymorphism.m calls calls lambda__transform_lambda directly.
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<p>
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The next pass is termination analysis. The various modules involved are:
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<ul>
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<li>
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termination.m is the control module. It sets the argument size and
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termination properties of builtin and compiler generated procedures,
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invokes term_pass1.m and term_pass2.m
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and writes .trans_opt files and error messages as appropriate.
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<li>
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term_pass1.m analyzes the argument size properties of user-defined procedures,
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<li>
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term_pass2.m analyzes the termination properties of user-defined procedures.
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<li>
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term_traversal.m contains code common to the two passes.
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<li>
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term_errors.m defines the various kinds of termination errors
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and prints the messages appropriate for each.
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<li>
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term_util.m defines the main types used in termination analysis
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and contains utility predicates.
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</ul>
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<p>
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Most of the remaining HLDS-to-HLDS transformations are optimizations:
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<ul>
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<li> specialization of higher-order predicates where the value of the
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higher-order arguments are known (higher_order.m)
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<li> inlining (i.e. unfolding) of simple procedures (inlining.m)
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<li> pushing constraints as far left as possible (constraint.m);
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this does not yet work.
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<li> issue warnings about unused arguments from predicates, and create
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specialized versions without them (unused_args.m); type_infos are
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often unused
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<li> elimination of dead procedures (dead_proc_elim.m). Inlining, higher-order
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specialization and the elimination of unused args can make procedures dead
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even the user doesn't, and automatically constructed unification and
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comparison predicates are often dead as well.
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<li> elimination of useless assignments, assignments that merely introduce
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another name for an already existing variable (excess.m).
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<li> reducing the number of variables that have to be saved across
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procedure calls (saved_vars.m). We do this by putting the code that
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generates the value of a variable just before the use of that variable,
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duplicating the variable and the code that produces it if necessary,
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provided the cost of doing so is smaller than the cost of saving and
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restoring the variable would be.
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</ul>
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<p>
|
|
|
|
The module transform.m contains stuff that is supposed to be useful
|
|
for high-level optimizations (but which is not yet used).
|
|
|
|
<p>
|
|
|
|
Eventually we plan to make Mercury the programming language of the Aditi
|
|
deductive database system. When this happens, we will need to be able to
|
|
apply the magic set transformation, which is defined for predicates
|
|
whose definitions are disjunctive normal form. The module dnf.m translates
|
|
definitions into DNF, introducing auxiliary predicates as necessary.
|
|
|
|
<p>
|
|
|
|
<h3> 4. Code generation </h3>
|
|
|
|
<p>
|
|
|
|
<dl>
|
|
<dt> pre-passes to annotate the HLDS
|
|
|
|
<dd>
|
|
Before code generation there are a few more passes which
|
|
annotate the HLDS with information used for code generation:
|
|
|
|
<dl>
|
|
<dt> choosing registers for procedure arguments (arg_info.m)
|
|
<dd>
|
|
Currently uses one of two simple algorithms, but
|
|
we may add other algorithms later.
|
|
<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 live_vars.m, which works
|
|
out which variables need to be saved on the
|
|
stack when, and then uses graph_colour.m to determine
|
|
a good allocation of variables to stack slots.
|
|
<dt> migration of builtins following branched structures
|
|
<dd>
|
|
This transformation, which is performed by
|
|
follow_code.m, improves the results of follow_vars.
|
|
<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.
|
|
</dl>
|
|
|
|
<dt> code generation
|
|
|
|
<dd>
|
|
For code generation itself, the main module is code_gen.m.
|
|
It handles conjunctions and negations, but calls sub-modules
|
|
to do most of the other work:
|
|
|
|
<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> 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
|
|
</ul>
|
|
<li> pragma_c_gen.m (embedded C code)
|
|
</ul>
|
|
<p>
|
|
|
|
It also calls middle_rec.m to do middle recursion optimization.
|
|
|
|
<p>
|
|
|
|
The code generation modules make use of
|
|
<dl>
|
|
<dt> code_info.m
|
|
<dd>
|
|
The main data structure for the code generator
|
|
<dt> code_exprn.m
|
|
<dd>
|
|
This defines the exprn_info type, which is
|
|
a sub-component of the code_info data structure
|
|
which holds the information about
|
|
the contents of registers and
|
|
the values/locations of variables.
|
|
<dt> exprn_aux.m
|
|
<dd>
|
|
Various preds which use exprn_info
|
|
<dt> code_util.m
|
|
<dd>
|
|
Some miscellaneous preds used for code generation
|
|
<dt> code_aux.m
|
|
<dd>
|
|
Some miscellaneous preds which, unlike those in
|
|
code_util, use code_info
|
|
<dt> continuation_info.m
|
|
<dd>
|
|
For accurate garbage collection, collects
|
|
information about each live value after calls,
|
|
and saves information about procedures.
|
|
</dl>
|
|
|
|
</dl>
|
|
|
|
<p>
|
|
|
|
The result of code generation is the Low Level Data Structure (llds.m).
|
|
The code is generated as a tree of code fragments which is then
|
|
flattened (tree.m).
|
|
|
|
<p>
|
|
|
|
<h3> 5. Low-level optimization </h3>
|
|
|
|
<p>
|
|
|
|
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 (dupelim.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> value numbering <br>
|
|
|
|
This is done by value_number.m, which has the following sub-modules:
|
|
|
|
<dl>
|
|
<dt> vn_block.m
|
|
<dd>
|
|
Traverse an extended basic block, building up tables showing
|
|
the actions that must be taken, and the current and desired
|
|
contents of locations.
|
|
<dt> vn_cost.m
|
|
<dd>
|
|
Computes the cost of instruction sequences.
|
|
Value numbering should never replace an instruction
|
|
sequence with a more expensive sequence. Unfortunately,
|
|
computing costs accurately is very difficult.
|
|
<dt> vn_debug.m
|
|
<dd>
|
|
Predicates to dump data structures used in value
|
|
numbering.
|
|
<dt> vn_filter.m
|
|
<dd>
|
|
Module to eliminate useless temporaries introduced by
|
|
value numbering. Not generating them in the first place
|
|
would be better, but would be quite difficult.
|
|
<dt> vn_flush.m
|
|
<dd>
|
|
Given the tables built up by vn_block and a list of nodes
|
|
computed by vn_order, generate code to assign the required
|
|
values to each temporary and live location in what is
|
|
hopefully the fastest and most compact way.
|
|
<dt> vn_order.m
|
|
<dd>
|
|
Given tables built up by vn_block showing the actions that
|
|
must be taken, and the current and desired contents of
|
|
locations, find out which shared subexpressions should
|
|
have temporaries allocated to them and in what order these
|
|
temporaries and the live locations should be assigned to.
|
|
This module uses the module atsort.m to perform an approximate
|
|
topological sort on the nodes of the location dependency
|
|
graph it operations on (since the graph may have cycles,
|
|
a precise topological sort may not exist).
|
|
<dt> vn_table.m
|
|
<dd>
|
|
Abstract data type showing the current and desired
|
|
contents of locations.
|
|
<dt> vn_temploc.m
|
|
<dd>
|
|
Abstract data type to keep track of the availability
|
|
of registers and temporaries.
|
|
<dt> vn_type.m
|
|
<dd>
|
|
This module defines the types used by the other
|
|
modules of the value numbering optimization.
|
|
<dt> vn_util.m
|
|
<dd>
|
|
Utility predicates.
|
|
<dt> vn_verify.m
|
|
<dd>
|
|
Sanity checks to make sure that (a) the optimized code
|
|
computes the same values as the original code, and (b)
|
|
the optimized code does not dereference tagged pointers
|
|
until the tag is known. (Violations of (b) usually cause
|
|
unaligned accesses, which cause bus errors on many machines.)
|
|
</dl>
|
|
|
|
Several of these modules (and also frameopt, above) use livemap.m,
|
|
which finds the set of locations live at each label.
|
|
</ul>
|
|
|
|
<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.
|
|
|
|
<p>
|
|
|
|
<h3> 6. Output C code </h3>
|
|
|
|
<ul>
|
|
<li> base_type_info.m generates the base_type_info structures that list the
|
|
unification, index and compare predicates associated with each declared
|
|
type constructor. These are added to the LLDS.
|
|
|
|
<li> base_type_layout.m generates the base_type_layout structures that give
|
|
information on how to interpret values of a given type. It also
|
|
creates base_type_functors structures that give information on
|
|
the functors of a given type. The base_type_layout and base_type_functors
|
|
structures of each declared type constructor are added to the LLDS.
|
|
|
|
<li> base_typeclass_info.m generates the base_typeclass_info structures that
|
|
list the methods of a class for each instance declaration. These are added to
|
|
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.
|
|
|
|
<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.
|
|
|
|
<li> Final generation of C code is done in llds_out.m.
|
|
</ul>
|
|
|
|
<hr>
|
|
<!-------------------------->
|
|
|
|
<p>
|
|
|
|
<h2> BYTECODE </h2>
|
|
|
|
<p>
|
|
|
|
The Mercury compiler can translate Mercury programs into bytecode for
|
|
interpretation by the Mercury debugger currently under development.
|
|
The generation of bytecode happens after semantic checks have been
|
|
completed.
|
|
|
|
<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.
|
|
</ul>
|
|
|
|
<hr>
|
|
<!-------------------------->
|
|
|
|
|
|
<h2> MISCELLANEOUS </h2>
|
|
|
|
<dl>
|
|
<dt> det_util:
|
|
<dd>
|
|
This module contains utility predicates needed by the parts
|
|
of the semantic analyzer and optimizer concerned with
|
|
determinism.
|
|
|
|
<dt> special_pred.m, unify_proc.m:
|
|
<dd>
|
|
These modules 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).
|
|
|
|
<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.
|
|
|
|
<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> opt_debug.m:
|
|
<dd>
|
|
Utility routines for debugging the LLDS-to-LLDS optimizations.
|
|
|
|
<dt> error_util.m:
|
|
<dd>
|
|
Utility routines for printing nicely formatted error messages.
|
|
</dl>
|
|
|
|
|
|
<hr>
|
|
<!-------------------------->
|
|
|
|
<p>
|
|
|
|
<h2> CURRENTLY USELESS </h2>
|
|
|
|
<p>
|
|
|
|
The following modules do not serve any function at the moment.
|
|
Some of them are obsolete; other are work-in-progress.
|
|
(For some of them its hard to say which!)
|
|
|
|
<dl>
|
|
<dt> lco.m:
|
|
<dd>
|
|
This finds predicates whose implementations would benefit
|
|
from last call optimization modulo constructor application.
|
|
It does not apply the optimization and will not until the
|
|
mode system is capable of expressing definite aliasing.
|
|
|
|
<dt> mercury_to_goedel.m:
|
|
<dd>
|
|
This converts from item_list to Goedel source code.
|
|
It works for simple programs, but doesn't handle
|
|
various Mercury constructs such as lambda expressions,
|
|
higher-order predicates, and functor overloading.
|
|
|
|
<dt> mercury_to_c.m:
|
|
<dd>
|
|
The very incomplete beginnings of an alternate
|
|
code generator. When finished, it will convert HLDS
|
|
to high-level C code (without going via LLDS).
|
|
|
|
</dl>
|
|
|
|
<hr>
|
|
<!-------------------------->
|
|
|
|
Last update was $Date: 1997-12-22 09:57:04 $ by $Author: zs $@cs.mu.oz.au. <br>
|
|
</body>
|
|
</html>
|