re PR tree-optimization/26260 (PTA is slow with large structs (hits clisp))

2006-02-14  Daniel Berlin  <dberlin@dberlin.org>

	Fix PR tree-optimization/26260

	* doc/invoke.texi (max-fields-for-field-sensitive): Document
	param.
	* params.h (MAX_FIELDS_FOR_FIELD_SENSITIVE): New.
	* params.def (PARAM_MAX_FIELDS_FOR_FIELD_SENSITIVE): Ditto.
	* tree-ssa-structalias.c (create_variable_info_for): Use
	MAX_FIELDS_FOR_FIELD_SENSITIVE.

From-SVN: r110972

gcc/ChangeLog

+2006-02-14  Daniel Berlin  <dberlin@dberlin.org>
+
+	Fix PR tree-optimization/26260
+
+	* doc/invoke.texi (max-fields-for-field-sensitive): Document
+	param.
+	* params.h (MAX_FIELDS_FOR_FIELD_SENSITIVE): New.
+	* params.def (PARAM_MAX_FIELDS_FOR_FIELD_SENSITIVE): Ditto.
+	* tree-ssa-structalias.c (create_variable_info_for): Use
+	MAX_FIELDS_FOR_FIELD_SENSITIVE.
+	
 2006-02-14  Zdenek Dvorak <dvorakz@suse.cz>
 
 	* doc/invoke.texi (-fprefetch-loop-arrays, -fprefetch-loop-arrays-rtl):

gcc/doc/invoke.texi

@@ -6195,6 +6195,11 @@ protection when @option{-fstack-protection} is used.
 @item max-jump-thread-duplication-stmts
 Maximum number of statements allowed in a block that needs to be
 duplicated when threading jumps.
+
+@item max-fields-for-field-sensitive
+Maximum number of fields in a structure we will treat in
+a field sensitive manner during pointer analysis.
+
 @end table
 @end table
 

gcc/params.def

@@ -559,6 +559,14 @@ DEFPARAM (PARAM_MAX_JUMP_THREAD_DUPLICATION_STMTS,
           "Maximum number of statements allowed in a block that needs to be duplicated when threading jumps",
 	  15, 0, 0)
 
+/* This is the maximum number of fields a variable may have before the pointer analysis machinery
+   will stop trying to treat it in a field-sensitive manner.  
+   There are programs out there with thousands of fields per structure, and handling them
+   field-sensitively is not worth the cost.  */
+DEFPARAM (PARAM_MAX_FIELDS_FOR_FIELD_SENSITIVE,
+          "max-fields-for-field-sensitive",
+	  "Maximum number of fields in a structure before pointer analysis treats the structure as a single variable",
+	  100, 0, 0)
 /*
 Local variables:
 mode:c

gcc/params.h

@@ -147,4 +147,6 @@ typedef enum compiler_param
   PARAM_VALUE (PARAM_MIN_VIRTUAL_MAPPINGS)
 #define VIRTUAL_MAPPINGS_TO_SYMS_RATIO \
   PARAM_VALUE (PARAM_VIRTUAL_MAPPINGS_TO_SYMS_RATIO)
+#define MAX_FIELDS_FOR_FIELD_SENSITIVE \
+  ((size_t) PARAM_VALUE (PARAM_MAX_FIELDS_FOR_FIELD_SENSITIVE))
 #endif /* ! GCC_PARAMS_H */

gcc/tree-ssa-structalias.c

@@ -3881,7 +3881,6 @@ check_for_overlaps (VEC (fieldoff_s,heap) *fieldstack)
     }
   return false;
 }
-
 /* Create a varinfo structure for NAME and DECL, and add it to VARMAP.
    This will also create any varinfo structures necessary for fields
    of DECL.  */
@@ -3945,7 +3944,8 @@ create_variable_info_for (tree decl, const char *name)
   if (use_field_sensitive 
       && !notokay 
       && !vi->is_unknown_size_var 
-      && var_can_have_subvars (decl))
+      && var_can_have_subvars (decl)
+      && VEC_length (fieldoff_s, fieldstack) <= MAX_FIELDS_FOR_FIELD_SENSITIVE)
     {
       unsigned int newindex = VEC_length (varinfo_t, varmap);
       fieldoff_s *fo = NULL;