re PR tree-optimization/28003 (optimizer bug)

2006-08-22  Daniel Berlin  <dberlin@dberlin.org>

	PR tree-optimization/28003
	* tree-ssa-alias.c (compute_may_aliases): Compute call clobbered
	before grouping aliases.

From-SVN: r116323

gcc/ChangeLog

+2006-08-22  Daniel Berlin  <dberlin@dberlin.org>
+
+	PR tree-optimization/28003
+	* tree-ssa-alias.c (compute_may_aliases): Compute call clobbered
+	before grouping aliases.
+
 2006-08-22  Roger Sayle  <roger@eyesopen.com>
 
 	* config/i386/i386.c (ix86_value_regno): Don't return FIRST_MMX_REG

gcc/testsuite/g++.dg/tree-ssa/pr28003.C

+// PR tree-optimization/28003
+// Alias grouping needs to be computed after call clobbering, because it
+// changes around the tags and variables in a way that makes our
+// call clobbering computation incorrect.
+// { dg-do run }
+// { dg-options "-O2" }
+extern "C" void abort(void);
+struct A
+{
+  int i, j[9];
+  A() : i(1) { j[0]=j[1]=j[2]=j[3]=j[4]=j[5]=j[6]=j[7]=j[8]=0; }
+};
+
+struct B
+{
+  A a;
+};
+
+B b[] =
+{
+  {}, {}, {}, {}, {}, {}, {}, {}, {}, {},
+  {}, {}, {}, {}, {}, {}, {}, {}, {}, {},
+  {}, {}, {}, {}, {}
+};
+
+int main()
+{
+  if (1 - b[sizeof(b)/sizeof(B) - 1].a.i != 0)
+    abort();
+  return 0;
+}

gcc/tree-ssa-alias.c

@@ -678,14 +678,14 @@ compute_may_aliases (void)
   /* Compute type-based flow-insensitive aliasing for all the type
      memory tags.  */
   compute_flow_insensitive_aliasing (ai);
+  
+  /* Compute call clobbering information.  */
+  compute_call_clobbered (ai);
 
   /* Determine if we need to enable alias grouping.  */
   if (ai->total_alias_vops >= MAX_ALIASED_VOPS)
     group_aliases (ai);
 
-  /* Compute call clobbering information.  */
-  compute_call_clobbered (ai);
-
   /* If the program has too many call-clobbered variables and/or function
      calls, create .GLOBAL_VAR and use it to model call-clobbering
      semantics at call sites.  This reduces the number of virtual operands