[PATCH] Fix PR43213

[Richard Guenther]

This fixes PR43213 - we probably miss this optimization because of
the expand from SSA changes.  The easiest fix is to just ask the
alias-oracle if the result-decl is aliased by the rhs.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.

Richard.

2010-03-01  Richard Guenther  <rguenther@suse.de>

	PR middle-end/43213
	* expr.c (expand_assignment): Use the alias-oracle to tell
	if the rhs aliases the result decl.

	* gcc.dg/pr43213.c: New testcase.

Index: gcc/testsuite/gcc.dg/pr43213.c
===================================================================
*** gcc/testsuite/gcc.dg/pr43213.c	(revision 0)
--- gcc/testsuite/gcc.dg/pr43213.c	(revision 0)
***************
*** 0 ****
--- 1,12 ----
+ /* { dg-do compile } */
+ 
+ struct S {
+   int i;
+ };
+ 
+ struct S f(int i)
+ {
+   return *(struct S *)&i;
+ }
+ 
+ /* { dg-final { scan-assembler-not "memmove" } } */
Index: gcc/expr.c
===================================================================
*** gcc/expr.c	(revision 157134)
--- gcc/expr.c	(working copy)
*************** expand_assignment (tree to, tree from, b
*** 4432,4440 ****
    /* In case we are returning the contents of an object which overlaps
       the place the value is being stored, use a safe function when copying
       a value through a pointer into a structure value return block.  */
!   if (TREE_CODE (to) == RESULT_DECL && TREE_CODE (from) == INDIRECT_REF
        && ADDR_SPACE_GENERIC_P
! 	  (TYPE_ADDR_SPACE (TREE_TYPE (TREE_TYPE (TREE_OPERAND (from, 0)))))
        && cfun->returns_struct
        && !cfun->returns_pcc_struct)
      {
--- 4432,4442 ----
    /* In case we are returning the contents of an object which overlaps
       the place the value is being stored, use a safe function when copying
       a value through a pointer into a structure value return block.  */
!   if (TREE_CODE (to) == RESULT_DECL
!       && TREE_CODE (from) == INDIRECT_REF
        && ADDR_SPACE_GENERIC_P
! 	   (TYPE_ADDR_SPACE (TREE_TYPE (TREE_TYPE (TREE_OPERAND (from, 0)))))
!       && refs_may_alias_p (to, from)
        && cfun->returns_struct
        && !cfun->returns_pcc_struct)
      {