tree-optimization/107107 - tail-merging VN wrong-code

The following fixes an unintended(?) side-effect of the special
MODIFY_EXPR expression entries we add for tail-merging during VN.
We shouldn't value-number the virtual operand differently here.

	PR tree-optimization/107107
	* tree-ssa-sccvn.cc (visit_reference_op_store): Do not
	affect value-numbering when doing the tail merging
	MODIFY_EXPR lookup.

	* gcc.dg/pr107107.c: New testcase.

1 files changed, 25 insertions, 0 deletions

diff --git a/gcc/testsuite/gcc.dg/pr107107.c b/gcc/testsuite/gcc.dg/pr107107.c
new file mode 100644
index 0000000..5ad6a63
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr107107.c
@@ -0,0 +1,25 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -ftree-tail-merge" } */
+
+static inline void set_longish(int is_long_long, void *p, long x)
+{
+  if (is_long_long)
+    *(long long*)p = x;
+  else
+    *(long*)p = x;
+}
+static long test(long long *p, int index, int mode)
+{
+  *p = 1;
+  set_longish(mode, p+index, 2);
+  return *p;
+}
+long (*volatile vtest)(long long*, int, int) = test;
+int main(void)
+{
+  long long x;
+  long result = vtest(&x, 0, 1);
+  if (result != 2 || x != 2)
+    __builtin_abort ();
+  return 0;
+}