re PR tree-optimization/91091 ([missed optimization] Missing optimization in unaliased pointers)

2019-07-05  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/91091
	* tree-ssa-sccvn.c (vn_reference_lookup_3): Overlap of
	accesses can happen with -fno-strict-aliasing.

	* gcc.dg/tree-ssa/pr91091-1.c: New testcase.
	* gcc.dg/tree-ssa/ssa-fre-61.c: Adjust.

From-SVN: r273134

gcc/ChangeLog

+2019-07-05  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/91091
+	* tree-ssa-sccvn.c (vn_reference_lookup_3): Overlap of
+	accesses can happen with -fno-strict-aliasing.
+
 2019-07-05  Jan Hubicka  <hubicka@ucw.cz>
 
 	* tree-ssa-alias.c (alias_stats): Add

gcc/testsuite/ChangeLog

+2019-07-05  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/91091
+	* gcc.dg/tree-ssa/pr91091-1.c: New testcase.
+	* gcc.dg/tree-ssa/ssa-fre-61.c: Adjust.
+
 2019-07-05  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* gnat.dg/pack23.adb, gnat.dg/pack23_pkg.ads: New testcase.

gcc/testsuite/gcc.dg/tree-ssa/pr91091-1.c

+/* { dg-do run } */
+/* { dg-options "-O3 -fno-strict-aliasing" } */
+
+struct s { int x; } __attribute__((packed));
+struct t { int x; };
+
+void __attribute__((noinline,noipa))
+swap(struct s* p, struct t* q)
+{
+  p->x = q->x;
+  q->x = p->x;
+}
+
+int main()
+{    
+  struct t a[2];
+  a[0].x = 0x12345678;
+  a[1].x = 0x98765432;
+  swap ((struct s *)((char *)a + 1), a);
+  if (a[0].x != 0x12345678)
+    __builtin_abort ();
+  return 0;
+}

gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-61.c

 /* { dg-do link } */
-/* { dg-options "-O -fdump-tree-fre1-details" } */
+/* { dg-options "-O -fstrict-aliasing -fdump-tree-fre1-details" } */
 
 void link_error (void);
 

gcc/tree-ssa-sccvn.c

@@ -1996,7 +1996,8 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
 	     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
+	      || (flag_strict_aliasing
+		  && get_alias_set (lhs) != 0
 		  && ao_ref_alias_set (ref) != 0)))
 	{
 	  tree *saved_last_vuse_ptr = data->last_vuse_ptr;