re PR tree-optimization/88223 (Wrong code for intrinsic memmove)

2018-11-28  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/88223
	* tree-ssa-sccvn.c (vn_reference_lookup_3): When skipping
	over a stored-same value may-alias store make sure to consider
	partial overlaps which are valid when TBAA reasonings do not
	apply and byte-granular overlaps are possible at all.

	* gcc.dg/torture/pr88223.c: New testcase.

From-SVN: r266560

gcc/ChangeLog

 2018-11-28  Richard Biener  <rguenther@suse.de>
 
+	PR tree-optimization/88223
+	* tree-ssa-sccvn.c (vn_reference_lookup_3): When skipping
+	over a stored-same value may-alias store make sure to consider
+	partial overlaps which are valid when TBAA reasonings do not
+	apply and byte-granular overlaps are possible at all.
+
+2018-11-28  Richard Biener  <rguenther@suse.de>
+
 	PR tree-optimization/88217
 	* vr-values.c (vr_values::extract_range_from_phi_node): Make
 	sure to handle results > +INF and < -INF correctly when

gcc/testsuite/ChangeLog

 2018-11-28  Richard Biener  <rguenther@suse.de>
 
+	PR tree-optimization/88223
+	* gcc.dg/torture/pr88223.c: New testcase.
+
+2018-11-28  Richard Biener  <rguenther@suse.de>
+
 	PR tree-optimization/88217
 	* g++.dg/pr88217.C: New testcase.
 

gcc/testsuite/gcc.dg/torture/pr88223.c

+/* { dg-do run } */
+
+extern void *memmove(void *, const void *, __SIZE_TYPE__);
+extern void abort(void);
+
+extern int
+main(void)
+{
+ char s[] = "12345";
+ memmove(s + 1, s, 4);
+ memmove(s + 1, s, 4);
+ memmove(s + 1, s, 4);
+ if (s[0] != '1' || s[1] != '1' || s[2] != '1' || s[3] != '1' || s[4] != '2')
+   abort ();
+ return (0);
+}

gcc/tree-ssa-sccvn.c

@@ -1927,7 +1927,16 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *vr_,
 	 VN_WALKREWRITE guard).  */
       if (vn_walk_kind == VN_WALKREWRITE
 	  && is_gimple_reg_type (TREE_TYPE (lhs))
-	  && types_compatible_p (TREE_TYPE (lhs), vr->type))
+	  && types_compatible_p (TREE_TYPE (lhs), vr->type)
+	  /* The overlap restriction breaks down when either access
+	     alias-set is zero.  Still for accesses of the size of
+	     an addressable unit there can be no overlaps.  Overlaps
+	     between different union members are not an issue since
+	     activation of a union member via a store makes the
+	     values of untouched bytes unspecified.  */
+	  && (known_eq (ref->size, BITS_PER_UNIT)
+	      || (get_alias_set (lhs) != 0
+		  && ao_ref_alias_set (ref) != 0)))
 	{
 	  tree *saved_last_vuse_ptr = last_vuse_ptr;
 	  /* Do not update last_vuse_ptr in vn_reference_lookup_2.  */