re PR tree-optimization/71452 (Wrong optimization of stores to _Bool via char*)

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.

From-SVN: r237214

gcc/ChangeLog

+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.
+
 2016-06-08  Jakub Jelinek  <jakub@redhat.com>
 	    Richard Biener  <rguenther@suse.de>
 

gcc/testsuite/ChangeLog

+2016-06-08  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/71452
+	* gcc.dg/torture/pr71452.c: New testcase.
+
 2016-06-08  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/71448

gcc/testsuite/gcc.dg/torture/pr71452.c

+/* { dg-do run } */
+
+int main()
+{
+  _Bool b;
+  *(char *)&b = 123;
+  if (*(char *)&b != 123)
+    __builtin_abort ();
+  return 0;
+}

gcc/tree-ssa.c

@@ -1292,6 +1292,14 @@ non_rewritable_lvalue_p (tree lhs)
       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;