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92966551f1
Estimated hours taken: 16
Branches: main
Replace the workaround for the bootstrapping problem with deep profiling grades
with a proper fix. The fix requires changing the builtin generic unify and
compare routines by removing the pretest comparing the two argument words
for equality. Since this can alter the algorithmic complexity of the program
(for the worse) which a profiler should definitely avoid, we compensate for
this by adding the pretest to the compiler-generated unify and compare
predicates. Since these pretests are executed even when the deleted pretest
wouldn't be, this can also alter algorithmic complexity (for the better)
at the cost of higher constant factors. However, the likelyhood of such
alteration is much smaller: if the top level of a term doesn't match, chances
are most of the function symbols at the lower levels won't match either.
In any case, the user has the option of getting this better algorithmic
complexity anyway by specifying the new option --should-pretest-equality.
However, until we have more experience with it, the documentation of the
new option is commented out.
runtime/mercury_conf_param.h:
Remove the workaround.
runtime/mercury_unify_compare_body.h:
Remove the problematic pretest, and document the problem that would
occur in its presence. Document the user_by_rtti dummy type
constructor. Fix some misleading abort messages.
compiler/options.m:
Add the --should-pretest-equality option.
Add (commented out) documentation for another option for which it was
missing.
doc/user_guide.texi:
Add (commented out) documentation for the new option, and for some
others which it was missing.
compiler/handle_options.m:
Make deep profiling imply the need for pretests in compiler generated
unify and compare predicates.
compiler/unify_proc.m:
If the new option is set, add pretests to unify and compare predicates.
We have to be careful to make sure that we don't add pretests if they
would try to unify two non-ground terms, or if the unification is
guaranteed to fail (since the casts in the pretest would obscure this
fact).
Implementing this required changing the approach of this module.
Instead of most predicates generating single clauses, they now generate
disjuncts for a disjunction that itself can be put inside the
if-then-else whose condition is the pretest. Since these predicates
not longer generate clauses, their names have been changed accordingly.
compiler/hlds_goal.m:
Add a goal feature for marking an if-then-else as representing
a pretest.
compiler/saved_vars.m:
Handle the new goal feature.
compiler/goal_util.m:
Add a function for stripping pretests away.
compiler/post_term_analysis.m:
compiler/term_constr_build.m:
compiler/term_pass1.m:
compiler/term_pass2.m:
Strip pretests away before termination analysis, since the analysis
can't yet prove termination in the presence of the pretest.
compiler/prog_type.m:
Add some auxilary predicates, and change the signature of an existing
predicate to make it more convenient to use.
compiler/type_util.m:
Conform to the change in prog_type.m, and in the process fix code to
avoid the assumption that the names of standard library modules are
unqualified (since the plan is to put them in package "std").
tests/hard_coded/profdeep_seg_fault.{m,exp}:
Fix the test case to be more readable and to generate properly
line-terminated output, now that we pass it.
BUGS:
Remove the entry for the bug fixed by this diff.
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[t_sig([t_typevar("BAR")], t_bool), t_sig([t_typevar("FOO")], t_bool), t_sig([t_bool], t_bool), t_sig([t_bool], t_bool)]
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