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5 Commits
| Author | SHA1 | Message | Date | |
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Zoltan Somogyi
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8693e293a2 |
This diff makes hlds_pred.m and many callers of its predicates easier to read
Estimated hours taken: 4 Branches: main This diff makes hlds_pred.m and many callers of its predicates easier to read and to maintain, but contains no changes in algorithms whatsoever. compiler/hlds_pred.m: Bring this module into line with our current coding standards. Use predmode declarations, functions, and state variable syntax when appropriate. Reorder arguments of predicates where necessary for the use of state variable syntax, and where this improves readability. Replace old-style lambdas with new-style lambdas or with partially applied named procedures. Standardize indentation. compiler/*.m: Conform to the changes in hlds_pred.m. This mostly means using the new argument orders of predicates exported by hlds_pred.m. Where this is now conveniently possible, change predicates to use state variable notation. In some modules, using state variable notation required changing the orders of arguments in the module's top predicate. compiler/passes_aux.m: Change the order of arguments in the calls this module makes to allow the callees to use state variable notation. Convert this module to state variable notation too. |
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Zoltan Somogyi
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01899e087b |
Do not allocate a stack slot to a variable just because it is live at an
Estimated hours taken: 0.5 Branches: main Do not allocate a stack slot to a variable just because it is live at an unsafe_cast generic_call. compiler/live_vars.m: Treat unsafe_casts as assignments. Convert the file to use state variable syntax, reordering arguments as required. compiler/call_gen.m: Document the reliance of live_vars.m on the absence of stack flushes at unsafe_casts. compiler/stack_alloc.m: Conform to the new argument order in live_vars.m. compiler/stack_opt.m: Conform to the new argument order in live_vars.m, and convert the predicate concerned to state variable syntax. |
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Zoltan Somogyi
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9551640f55 |
Import only one compiler module per line. Sort the blocks of imports.
Estimated hours taken: 2 Branches: main compiler/*.m: Import only one compiler module per line. Sort the blocks of imports. This makes it easier to merge in changes. In a couple of places, remove unnecessary imports. |
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Zoltan Somogyi
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ed83fe4623 |
Optimize shallow traced modules by not adding calls to MR_trace to shallow
Estimated hours taken: 12
Branches: main
Optimize shallow traced modules by not adding calls to MR_trace to shallow
traced procedures which cannot be called from a deep traced environment.
A shallow traced procedure can be optimized in this way if it is neither
exported from its defining module nor has its address taken.
The main purpose of this optimization is not the avoidance of the cost of the
MR_trace calls as much as it is the restoration of tail recursion optimization.
Previously, compiling a program in a debug grade would disable all tail
recursion in the program (since debug grades require at least shallow tracing
every module). This was a problem because it limited the sizes of the inputs
the debugged program could process before running out of memory. As long as
the procedures that recurse on the input are in the implementation section
of a shallow traced module, this should no longer happen.
compiler/trace_params.m:
Introduce the concept of a procedure's effective trace level. This is
identical to the global trace level, except if the procedure is not
exported and doesn't have its address taken, and the global trace level
is shallow. In that case, we say that the procedure's effective trace
level is none.
Computing a procedure's effective trace level requires its proc_info
and its parent pred_info, so require callers to supply these as
parameters.
compiler/code_info.m:
Store the current pred_info as well as the current proc_info, for
trace parameter lookups.
compiler/continuation_info.m:
compiler/code_gen.m:
Record the required trace parameters of a procedure in its layout
structure, since it can no longer be computed from the global trace
level.
compiler/stack_layout.m:
Use the trace parameters in procedures' layout structures, instead of
trying to compute them from the global trace level.
compiler/inlining.m:
compiler/liveness.m:
compiler/stack_alloc.m:
compiler/store_alloc.m:
compiler/trace.m:
Use procedures' effective trace level instead of the global trace level
where relevant.
compiler/llds.m:
Record the required trace parameter of a procedure in its c_procedure
representation, since it can no longer be computed from the global
trace level.
Delete an obsolete field.
compiler/optimize.m:
compiler/jumpopt.m:
Use a required trace parameter of a procedure in its c_procedure
representation, since it can no longer be computed from the global
trace level.
compiler/compile_target_code.m:
compiler/handle_options.m:
compiler/llds_out.m:
compiler/mercury_compile.m:
Trivial changes to conform to updated interfaces.
compiler/stack_opt.m:
Use the option opt_no_return_calls, instead of approximating it
with the trace level. (The old code was a holdover from before the
creation of the option.)
tests/debugger/shallow.m:
tests/debugger/shallow2.m:
tests/debugger/shallow.{inp,exp*}:
Divide the old test case in shallow.m in two. The top level predicates
stay in shallow.m and continue to be shallow traced. The two bottom
predicates move to shallow2.m and are now deep traced.
The new test input checks whether the debugger can walk across the
stack frames of procedures in shallow traced modules whose effective
trace level is "none" (such as queen/2).
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Zoltan Somogyi
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189b9215ae |
This diff implements stack slot optimization for the LLDS back end based on
Estimated hours taken: 400
Branches: main
This diff implements stack slot optimization for the LLDS back end based on
the idea that after a unification such as A = f(B, C, D), saving the
variable A on the stack indirectly also saves the values of B, C and D.
Figuring out what subset of {B,C,D} to access via A and what subset to access
via their own stack slots is a tricky optimization problem. The algorithm we
use to solve it is described in the paper "Using the heap to eliminate stack
accesses" by Zoltan Somogyi and Peter Stuckey, available in ~zs/rep/stackslot.
That paper also describes (and has examples of) the source-to-source
transformation that implements the optimization.
The optimization needs to know what variables are flushed at call sites
and at program points that establish resume points (e.g. entries to
disjunctions and if-then-elses). We already had code to compute this
information in live_vars.m, but this code was being invoked too late.
This diff modifies live_vars.m to allow it to be invoked both by the stack
slot optimization transformation and by the code generator, and allows its
function to be tailored to the requirements of each invocation.
The information computed by live_vars.m is specific to the LLDS back end,
since the MLDS back ends do not (yet) have the same control over stack
frame layout. We therefore store this information in a new back end specific
field in goal_infos. For uniformity, we make all the other existing back end
specific fields in goal_infos, as well as the similarly back end specific
store map field of goal_exprs, subfields of this new field. This happens
to significantly reduce the sizes of goal_infos.
To allow a more meaningful comparison of the gains produced by the new
optimization, do not save any variables across erroneous calls even if
the new optimization is not enabled.
compiler/stack_opt.m:
New module containing the code that performs the transformation
to optimize stack slot usage.
compiler/matching.m:
New module containing an algorithm for maximal matching in bipartite
graphs, specialized for the graphs needed by stack_opt.m.
compiler/mercury_compile.m:
Invoke the new optimization if the options ask for it.
compiler/stack_alloc.m:
New module containing code that is shared between the old,
non-optimizing stack slot allocation system and the new, optimizing
stack slot allocation system, and the code for actually allocating
stack slots in the absence of optimization.
Live_vars.m used to have two tasks: find out what variables need to be
saved on the stack, and allocating those variables to stack slots.
Live_vars.m now does only the first task; stack_alloc.m now does
the second, using code that used to be in live_vars.m.
compiler/trace_params:
Add a new function to test the trace level, which returns yes if we
want to preserve the values of the input headvars.
compiler/notes/compiler_design.html:
Document the new modules (as well as trace_params.m, which wasn't
documented earlier).
compiler/live_vars.m:
Delete the code that is now in stack_alloc.m and graph_colour.m.
Separate out the kinds of stack uses due to nondeterminism: the stack
slots used by nondet calls, and the stack slots used by resumption
points, in order to allow the reuse of stack slots used by resumption
points after execution has left their scope. This should allow the
same stack slots to be used by different variables in the resumption
point at the start of an else branch and nondet calls in the then
branch, since the resumption point of the else branch is not in effect
when the then branch is executed.
If the new option --opt-no-return-calls is set, then say that we do not
need to save any values across erroneous calls.
Use type classes to allow the information generated by this module
to be recorded in the way required by its invoker.
Package up the data structures being passed around readonly into a
single tuple.
compiler/store_alloc.m:
Allow this module to be invoked by stack_opt.m without invoking the
follow_vars transformation, since applying follow_vars before the form
of the HLDS code is otherwise final can be a pessimization.
Make the module_info a part of the record containing the readonly data
passed around during the traversal.
compiler/common.m:
Do not delete or move around unifications created by stack_opt.m.
compiler/call_gen.m:
compiler/code_info.m:
compiler/continuation_info.m:
compiler/var_locn.m:
Allow the code generator to delete its last record of the location
of a value when generating code to make an erroneous call, if the new
--opt-no-return-calls option is set.
compiler/code_gen.m:
Use a more useful algorithm to create the messages/comments that
we put into incr_sp instructions, e.g. by distinguishing between
predicates and functions. This is to allow the new scripts in the
tool directory to gather statistics about the effect of the
optimization on stack frame sizes.
library/exception.m:
Make a hand-written incr_sp follow the new pattern.
compiler/arg_info.m:
Add predicates to figure out the set of input, output and unused
arguments of a procedure in several different circumstances.
Previously, variants of these predicates were repeated in several
places.
compiler/goal_util.m:
Export some previously private utility predicates.
compiler/handle_options.m:
Turn off stack slot optimizations when debugging, unless
--trace-optimized is set.
Add a new dump format useful for debugging --optimize-saved-vars.
compiler/hlds_llds.m:
New module for handling all the stuff specific to the LLDS back end
in HLDS goal_infos.
compiler/hlds_goal.m:
Move all the relevant stuff into the new back end specific field
in goal_infos.
compiler/notes/allocation.html:
Update the documentation of store maps to reflect their movement
into a subfield of goal_infos.
compiler/*.m:
Minor changes to accomodate the placement of all back end specific
information about goals from goal_exprs and individual fields of
goal_infos into a new field in goal_infos that gathers together
all back end specific information.
compiler/use_local_vars.m:
Look for sequences in which several instructions use a fake register
or stack slot as a base register pointing to a cell, and make those
instructions use a local variable instead.
Without this, a key assumption of the stack slot optimization,
that accessing a field in a cell costs only one load or store
instruction, would be much less likely to be true. (With this
optimization, the assumption will be false only if the C compiler's
code generator runs out of registers in a basic block, which for
the code we generate should be unlikely even on x86s.)
compiler/options.m:
Make the old option --optimize-saved-vars ask for both the old stack
slot optimization (implemented by saved_vars.m) that only eliminates
the storing of constants in stack slots, and the new optimization.
Add two new options --optimize-saved-vars-{const,cell} to turn on
the two optimizations separately.
Add a bunch of options to specify the parameters of the new
optimizations, both in stack_opt.m and use_local_vars.m. These are
for implementors only; they are deliberately not documented.
Add a new option, --opt-no-return-cells, that governs whether we avoid
saving variables on the stack at calls that cannot return, either by
succeeding or by failing. This is for implementors only, and thus
deliberately documented only in comments. It is enabled by default.
compiler/optimize.m:
Transmit the value of a new option to use_local_vars.m.
doc/user_guide.texi:
Update the documentation of --optimize-saved-vars.
library/tree234.m:
Undo a previous change of mine that effectively applied this
optimization by hand. That change complicated the code, and now
the compiler can do the optimization automatically.
tools/extract_incr_sp:
A new script for extracting stack frame sizes and messages from
stack increment operations in the C code for LLDS grades.
tools/frame_sizes:
A new script that uses extract_incr_sp to extract information about
stack frame sizes from the C files saved from a stage 2 directory
by makebatch and summarizes the resulting information.
tools/avg_frame_size:
A new script that computes average stack frame sizes from the files
created by frame_sizes.
tools/compare_frame_sizes:
A new script that compares the stack frame size information
extracted from two different stage 2 directories by frame_sizes,
reporting on both average stack frame sizes and on specific procedures
that have different stack frame sizes in the two versions.
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