re PR tree-optimization/70701 (incomplete value numbering when memcpy-ing from array)

2016-04-18  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/70701
	* tree-ssa-sccvn.c (vn_reference_lookup_3): Resolve fully constant
	references after translating through a memcpy.

	* gcc.dg/tree-ssa/ssa-fre-53.c: New testcase.

From-SVN: r235131

gcc/ChangeLog

 2016-04-18  Richard Biener  <rguenther@suse.de>
 
+	PR tree-optimization/70701
+	* tree-ssa-sccvn.c (vn_reference_lookup_3): Resolve fully constant
+	references after translating through a memcpy.
+
+2016-04-18  Richard Biener  <rguenther@suse.de>
+
 	* tree-ssa-pre.c (postorder, postorder_num): Make locals ...
 	(compute_antic): ... here.  For partial antic use regular
 	postorder and scrap iteration.

gcc/testsuite/ChangeLog

+2016-04-18  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/70701
+	* gcc.dg/tree-ssa/ssa-fre-53.c: New testcase.
+
 2016-04-18  Tom de Vries  <tom@codesourcery.com>
 
 	PR testsuite/70699

gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-53.c

+/* { dg-do compile } */
+/* { dg-options "-O -fno-tree-forwprop -fdump-tree-fre1" } */
+
+const int a[]={1,2,3};
+int f(){
+    int*b=__builtin_malloc(12);
+    __builtin_memcpy(b,a,12);
+    return b[0];
+}
+
+/* { dg-final { scan-tree-dump "return 1;" "fre1" } } */

gcc/tree-ssa-sccvn.c

@@ -2152,6 +2152,12 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *vr_,
       vr->operands[1] = op;
       vr->hashcode = vn_reference_compute_hash (vr);
 
+      /* Try folding the new reference to a constant.  */
+      tree val = fully_constant_vn_reference_p (vr);
+      if (val)
+	return vn_reference_lookup_or_insert_for_pieces
+		 (vuse, vr->set, vr->type, vr->operands, val);
+
       /* Adjust *ref from the new operands.  */
       if (!ao_ref_init_from_vn_reference (&r, vr->set, vr->type, vr->operands))
 	return (void *)-1;