[m-rev.] diff: trail usage analysis of compiler generated special preds

[Julien Fischer]

Estimated hours taken: 1
Branches: main

Make the trail usage analysis less conservative with respect to compiler
generated special predicates.  This increases the speed of a compiler built in
hlc.gc.tr with --intermodule-optimzation and trail usage analysis by about
3.5% and decreases the executable size by 5.2%.

compiler/trailing_analysis.m:
	Do not assume that type-specific compiler generated unification and
	comparison predicates always modify the trail; some of them, e.g.
	those for enumerations, do not.

	Delete this item from the TODO list.

compiler/mode_info.m:
	Unrelated change: fix indentation in a spot.

compiler/ml_code_gen.m:
	Unrelated change: s/Word/MR_Word/.

Julien.

Index: compiler/ml_code_gen.m
===================================================================
RCS file: /home/mercury1/repository/mercury/compiler/ml_code_gen.m,v
retrieving revision 1.166
diff -u -r1.166 ml_code_gen.m
--- compiler/ml_code_gen.m	8 Dec 2005 06:14:35 -0000	1.166
+++ compiler/ml_code_gen.m	21 Dec 2005 02:34:48 -0000
@@ -3125,7 +3125,7 @@
         ;
             HighLevelData = no,
             % For --no-high-level-data, we only need to use a cast is for
-            % polymorphic types, which are `Word' in the C interface but
+            % polymorphic types, which are `MR_Word' in the C interface but
             % `MR_Box' in the MLDS back-end.
             (
                 ( OrigType = variable(_, _)
Index: compiler/mode_info.m
===================================================================
RCS file: /home/mercury1/repository/mercury/compiler/mode_info.m,v
retrieving revision 1.80
diff -u -r1.80 mode_info.m
--- compiler/mode_info.m	14 Dec 2005 05:14:14 -0000	1.80
+++ compiler/mode_info.m	21 Dec 2005 06:24:51 -0000
@@ -409,7 +409,7 @@
     module_info_get_globals(ModuleInfo, Globals),
     globals__lookup_bool_option(Globals, debug_modes, DebugModes),
     globals__lookup_int_option(Globals, debug_modes_pred_id,
-    DebugModesPredId),
+        DebugModesPredId),
     pred_id_to_int(PredId, PredIdInt),
     (
         DebugModes = yes,
Index: compiler/trailing_analysis.m
===================================================================
RCS file: /home/mercury1/repository/mercury/compiler/trailing_analysis.m,v
retrieving revision 1.3
diff -u -r1.3 trailing_analysis.m
--- compiler/trailing_analysis.m	6 Dec 2005 06:26:07 -0000	1.3
+++ compiler/trailing_analysis.m	23 Dec 2005 03:16:17 -0000
@@ -45,8 +45,6 @@
 %   - Use the results of closure analysis to determine the trailing
 %     status of higher-order calls.
 %   - Improve the analysis in the presence of solver types.
-%   - Lift some of the restrictions on compiler-generated unification and
-%     comparison preds.
 %   - Create specialised versions of higher-order procedures based on
 %     whether or not their arguments modify the trail.

@@ -287,27 +285,20 @@
         % There are no builtins that will modify the trail.
         Result = will_not_modify_trail
     ;
-        % Handle unify and compare.
-        (
-            ModuleName = pred_info_module(CallPredInfo),
-            any_mercury_builtin_module(ModuleName),
-            Name = pred_info_name(CallPredInfo),
-            Arity = pred_info_orig_arity(CallPredInfo),
-            ( SpecialPredId = spec_pred_compare
-            ; SpecialPredId = spec_pred_unify
-            ),
-            special_pred_name_arity(SpecialPredId, Name, _, Arity)
-        ;
-            % XXX This is too conservative.
-            pred_info_get_origin(CallPredInfo, Origin),
-            Origin = special_pred(SpecialPredId - _),
-            ( SpecialPredId = spec_pred_compare
-            ; SpecialPredId = spec_pred_unify
-            )
-        )
+        % Handle builtin unify and compare.
+        % NOTE: the type specific unify and compare predicates are just
+        % treated as though they were normal predicates.
+        ModuleName = pred_info_module(CallPredInfo),
+        any_mercury_builtin_module(ModuleName),
+        Name = pred_info_name(CallPredInfo),
+        Arity = pred_info_orig_arity(CallPredInfo),
+        ( SpecialPredId = spec_pred_compare
+        ; SpecialPredId = spec_pred_unify
+        ),
+        special_pred_name_arity(SpecialPredId, Name, _, Arity)
     ->
-        % At the moment we assume that calls to out-of-line
-        % unification/comparisons are going to modify the trail.
+        % XXX We should examine the argument types of calls to builtin.unify/2
+        % and builtin.compare/3 and then make a decision based on those.
         Result = may_modify_trail
     ;
         % Handle library predicates whose trailing status
@@ -712,23 +703,15 @@
     ->
         Status = will_not_modify_trail
     ;
-        % Handle unify and compare.
-        (
-            ModuleName = pred_info_module(CallPredInfo),
-            any_mercury_builtin_module(ModuleName),
-            Name = pred_info_name(CallPredInfo),
-            Arity = pred_info_orig_arity(CallPredInfo),
-            ( SpecialPredId = spec_pred_compare
-            ; SpecialPredId = spec_pred_unify
-            ),
-            special_pred_name_arity(SpecialPredId, Name, _, Arity)
-        ;
-            pred_info_get_origin(CallPredInfo, Origin),
-            Origin = special_pred(SpecialPredId - _),
-            ( SpecialPredId = spec_pred_compare
-            ; SpecialPredId = spec_pred_unify
-            )
-        )
+        % Handle builtin unify and compare.
+        ModuleName = pred_info_module(CallPredInfo),
+        any_mercury_builtin_module(ModuleName),
+        Name = pred_info_name(CallPredInfo),
+        Arity = pred_info_orig_arity(CallPredInfo),
+        ( SpecialPredId = spec_pred_compare
+        ; SpecialPredId = spec_pred_unify
+        ),
+        special_pred_name_arity(SpecialPredId, Name, _, Arity)
     ->
         Status = may_modify_trail
     ;

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