[PATCH] Fix PR71452

[Richard Biener <rguenther@suse.de>]

The following fixes a bug when rewriting a memory location into SSA
form.  For the testcase we didn't consider the case where the type
we end up using for the SSA name does not have enough precision
to cover all values of the dynamic type (thus we only need to consider
stores).

Bootstrap and regtest running on x86_64-unknown-linux-gnu.

Richard.

2016-06-08  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/71452
	* tree-ssa.c (non_rewritable_lvalue_p): Make sure that the
	type used for the SSA rewrite has enough precision to cover
	the dynamic type of the location.

	* gcc.dg/torture/pr71452.c: New testcase.

Index: gcc/tree-ssa.c
===================================================================
*** gcc/tree-ssa.c	(revision 237196)
--- gcc/tree-ssa.c	(working copy)
*************** non_rewritable_lvalue_p (tree lhs)
*** 1292,1297 ****
--- 1320,1333 ----
        if (integer_zerop (TREE_OPERAND (lhs, 1))
  	  && DECL_P (decl)
  	  && DECL_SIZE (decl) == TYPE_SIZE (TREE_TYPE (lhs))
+ 	  /* If the dynamic type of the decl has larger precision than
+ 	     the decl itself we can't use the decls type for SSA rewriting.  */
+ 	  && ((! INTEGRAL_TYPE_P (TREE_TYPE (decl))
+ 	       || compare_tree_int (DECL_SIZE (decl),
+ 				    TYPE_PRECISION (TREE_TYPE (decl))) == 0)
+ 	      || (INTEGRAL_TYPE_P (TREE_TYPE (lhs))
+ 		  && (TYPE_PRECISION (TREE_TYPE (decl))
+ 		      >= TYPE_PRECISION (TREE_TYPE (lhs)))))
  	  && (TREE_THIS_VOLATILE (decl) == TREE_THIS_VOLATILE (lhs)))
  	return false;
  
Index: gcc/testsuite/gcc.dg/torture/pr71452.c
===================================================================
*** gcc/testsuite/gcc.dg/torture/pr71452.c	(revision 0)
--- gcc/testsuite/gcc.dg/torture/pr71452.c	(working copy)
***************
*** 0 ****
--- 1,10 ----
+ /* { dg-do run } */
+ 
+ int main()
+ {
+   _Bool b;
+   *(char *)&b = 123;
+   if (*(char *)&b != 123)
+     __builtin_abort ();
+   return 0;
+ }
Index: gcc/testsuite/g++.dg/torture/pr71452.C
===================================================================
*** gcc/testsuite/g++.dg/torture/pr71452.C	(revision 0)
--- gcc/testsuite/g++.dg/torture/pr71452.C	(working copy)
***************
*** 0 ****
--- 1,10 ----
+ // { dg-do run }
+ 
+ int main()
+ {
+   bool b;
+   *(char *)&b = 123;
+   if (*(char *)&b != 123)
+     __builtin_abort ();
+   return 0;
+ }