[PATCH] Fix PR81977

[Richard Biener]

The following fixes a failure to account for lhs_offset (or rather
to consistently use the same offset in op0 and off).

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.

Richard.

2017-08-28  Richard Biener  <rguent...@suse.de>

        PR tree-optimization/81977
        * tree-ssa-sccvn.c (vn_reference_lookup_3): Fix look through
        memcpy.

        * g++.dg/torture/pr81977.C: New testcase.

Index: gcc/tree-ssa-sccvn.c
===================================================================
--- gcc/tree-ssa-sccvn.c        (revision 251377)
+++ gcc/tree-ssa-sccvn.c        (working copy)
@@ -2334,7 +2334,7 @@ vn_reference_lookup_3 (ao_ref *ref, tree
       memset (&op, 0, sizeof (op));
       op.type = vr->type;
       op.opcode = MEM_REF;
-      op.op0 = build_int_cst (ptr_type_node, at - rhs_offset);
+      op.op0 = build_int_cst (ptr_type_node, at - lhs_offset + rhs_offset);
       op.off = at - lhs_offset + rhs_offset;
       vr->operands[0] = op;
       op.type = TREE_TYPE (rhs);
Index: gcc/testsuite/g++.dg/torture/pr81977.C
===================================================================
--- gcc/testsuite/g++.dg/torture/pr81977.C      (nonexistent)
+++ gcc/testsuite/g++.dg/torture/pr81977.C      (working copy)
@@ -0,0 +1,55 @@
+/* { dg-do run } */
+/* { dg-require-effective-target int32plus } */
+
+#include <cstdint>
+
+typedef struct
+{
+  uint16_t  x ;
+  uint16_t  y ;
+  uint64_t  z ;
+} __attribute__((packed, aligned(1))) TestMsgType;
+
+struct Payload
+{
+  uint16_t header_info[2];
+  TestMsgType _pref;
+  void Pack(uint8_t *buffer)
+    {
+      __builtin_memcpy(buffer, &_pref, sizeof(_pref));
+    }
+  void UnPack(uint8_t *buffer)
+    {
+      __builtin_memcpy(&_pref, buffer, sizeof(_pref));
+    }
+};
+
+
+struct Msg
+{
+  Payload _payload;
+  void Pack(uint8_t *buffer)
+    {
+      _payload.Pack(buffer);
+    }
+
+  void UnPack(uint8_t *buffer)
+    {
+      _payload.UnPack(buffer);
+    }
+};
+
+int main()
+{
+  uint8_t * buffer = new uint8_t [30];
+  Msg msg;
+  Msg msg1;
+  msg._payload._pref.x             = 0xabcd;
+  msg._payload._pref.y             = 0xa;
+  msg._payload._pref.z             = 0x0001020304051617;
+  msg.Pack(&buffer[0]);
+  msg1.UnPack(&buffer[0]);
+  if (msg1._payload._pref.x != 0xabcd)
+    __builtin_abort ();
+  delete [] buffer;
+}