2009-04-07 Richard Guenther <rguenther@suse.de>

	* tree-ssa-alias.c (ref_maybe_used_by_call_p_1): Non-aliased
	decls are only used if passes as parameters or if they are
	local statics and the call is not to a builtin.
	(call_may_clobber_ref_p_1): Likewise.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@145676 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 31 insertions, 2 deletions

diff --git a/gcc/tree-ssa-alias.c b/gcc/tree-ssa-alias.c
index a85858e17af..f97502a606a 100644
--- a/gcc/tree-ssa-alias.c
+++ b/gcc/tree-ssa-alias.c
@@ -737,7 +737,7 @@ refs_may_alias_p (tree ref1, tree ref2)
 static bool
 ref_maybe_used_by_call_p_1 (gimple call, tree ref)
 {
-  tree base;
+  tree base, fndecl;
   unsigned i;
   int flags = gimple_call_flags (call);
 
@@ -754,6 +754,20 @@ ref_maybe_used_by_call_p_1 (gimple call, tree ref)
       || !DECL_P (base))
     return true;
 
+  /* If the reference is based on a decl that is not aliased the call
+     cannot possibly use it.  */
+  if (DECL_P (base)
+      && !may_be_aliased (base)
+      /* But local statics can be used through recursion!  */
+      && (!is_global_var (base)
+	  /* But not via builtins.
+	     ???  We just assume that this is true if we are not a
+	     builtin function ourself.  */
+	  || (!DECL_BUILT_IN (cfun->decl)
+	      && (fndecl = gimple_call_fndecl (call))
+	      && DECL_BUILT_IN (fndecl))))
+    goto process_args;
+
   /* Check if base is a global static variable that is not read
      by the function.  */
   if (TREE_CODE (base) == VAR_DECL
@@ -851,7 +865,7 @@ ref_maybe_used_by_stmt_p (gimple stmt, tree ref)
 static bool
 call_may_clobber_ref_p_1 (gimple call, tree ref)
 {
-  tree base;
+  tree fndecl, base;
 
   /* If the call is pure or const it cannot clobber anything.  */
   if (gimple_call_flags (call)
@@ -866,6 +880,21 @@ call_may_clobber_ref_p_1 (gimple call, tree ref)
       || CONSTANT_CLASS_P (base))
     return false;
 
+  /* If the reference is based on a decl that is not aliased the call
+     cannot possibly clobber it.  */
+  if (DECL_P (base)
+      && !may_be_aliased (base)
+      /* But local non-readonly statics can be modified through recursion!  */
+      && (TREE_READONLY (base)
+	  || !is_global_var (base)
+	  /* But not via builtins.
+	     ???  We just assume that this is true if we are not a
+	     builtin function ourself.  */
+	  || (!DECL_BUILT_IN (cfun->decl)
+	      && (fndecl = gimple_call_fndecl (call))
+	      && DECL_BUILT_IN (fndecl))))
+    return false;
+
   /* Check if base is a global static variable that is not written
      by the function.  */
   if (TREE_CODE (base) == VAR_DECL