[gcc r13-3126] tree-optimization/107107 - tail-merging VN wrong-code

[Richard Biener <rguenth@gcc.gnu.org>]

https://gcc.gnu.org/g:85333b9265720fc4e49397301cb16324d2b89aa7

commit r13-3126-g85333b9265720fc4e49397301cb16324d2b89aa7
Author: Richard Biener <rguenther@suse.de>
Date:   Thu Oct 6 11:20:16 2022 +0200

    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.

Diff:
---
 gcc/testsuite/gcc.dg/pr107107.c | 25 +++++++++++++++++++++++++
 gcc/tree-ssa-sccvn.cc           | 17 +++--------------
 2 files changed, 28 insertions(+), 14 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/pr107107.c b/gcc/testsuite/gcc.dg/pr107107.c
new file mode 100644
index 00000000000..5ad6a63159e
--- /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;
+}
diff --git a/gcc/tree-ssa-sccvn.cc b/gcc/tree-ssa-sccvn.cc
index 2cc2c0e1e34..37484403c56 100644
--- a/gcc/tree-ssa-sccvn.cc
+++ b/gcc/tree-ssa-sccvn.cc
@@ -5718,19 +5718,6 @@ visit_reference_op_store (tree lhs, tree op, gimple *stmt)
 
   if (!resultsame)
     {
-      /* Only perform the following when being called from PRE
-	 which embeds tail merging.  */
-      if (default_vn_walk_kind == VN_WALK)
-	{
-	  assign = build2 (MODIFY_EXPR, TREE_TYPE (lhs), lhs, op);
-	  vn_reference_lookup (assign, vuse, VN_NOWALK, &vnresult, false);
-	  if (vnresult)
-	    {
-	      VN_INFO (vdef)->visited = true;
-	      return set_ssa_val_to (vdef, vnresult->result_vdef);
-	    }
-	}
-
       if (dump_file && (dump_flags & TDF_DETAILS))
 	{
 	  fprintf (dump_file, "No store match\n");
@@ -5755,7 +5742,9 @@ visit_reference_op_store (tree lhs, tree op, gimple *stmt)
       if (default_vn_walk_kind == VN_WALK)
 	{
 	  assign = build2 (MODIFY_EXPR, TREE_TYPE (lhs), lhs, op);
-	  vn_reference_insert (assign, lhs, vuse, vdef);
+	  vn_reference_lookup (assign, vuse, VN_NOWALK, &vnresult, false);
+	  if (!vnresult)
+	    vn_reference_insert (assign, lhs, vuse, vdef);
 	}
     }
   else