[PATCH] tree-optimization/112827 - corrupt SCEV cache during SCCP

[Richard Biener]

The following avoids corrupting the SCEV cache by my last change
to propagate constant final values immediately.  The easiest fix
is to keep a dead initialization around.

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.

        PR tree-optimization/112827
        * tree-scalar-evolution.cc (final_value_replacement_loop):
        Do not release SSA name but keep a dead initialization around.

        * gcc.dg/torture/pr112827-1.c: New testcase.
        * gcc.dg/torture/pr112827-2.c: Likewise.
---
 gcc/testsuite/gcc.dg/torture/pr112827-1.c | 14 ++++++++++++++
 gcc/testsuite/gcc.dg/torture/pr112827-2.c | 18 ++++++++++++++++++
 gcc/tree-scalar-evolution.cc              |  9 +++------
 3 files changed, 35 insertions(+), 6 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/torture/pr112827-1.c
 create mode 100644 gcc/testsuite/gcc.dg/torture/pr112827-2.c

diff --git a/gcc/testsuite/gcc.dg/torture/pr112827-1.c 
b/gcc/testsuite/gcc.dg/torture/pr112827-1.c
new file mode 100644
index 00000000000..6838cbbe62f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr112827-1.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+
+int a, b, c, d, e;
+int main() {
+  for (; c; c++) {
+    for (a = 0; a < 2; a++)
+      ;
+    for (; b; b++) {
+      e = d;
+      d = a;
+    }
+  }
+  return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/torture/pr112827-2.c 
b/gcc/testsuite/gcc.dg/torture/pr112827-2.c
new file mode 100644
index 00000000000..a7a2a70211b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr112827-2.c
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+
+short a, b[1], f;
+char c, g;
+int d, e;
+int main() {
+  for (; f; f++) {
+    for (d = 0; d < 2; d++)
+      ;
+    if (a)
+      for (g = 0; g < 2; g++)
+        for (c = 0; c < 2; c += b[d+g])
+          ;
+    for (; e; e++)
+      ;
+  }
+  return 0;
+}
diff --git a/gcc/tree-scalar-evolution.cc b/gcc/tree-scalar-evolution.cc
index 065bcd0743d..7556d89e9f8 100644
--- a/gcc/tree-scalar-evolution.cc
+++ b/gcc/tree-scalar-evolution.cc
@@ -3847,13 +3847,10 @@ final_value_replacement_loop (class loop *loop)
       def = unshare_expr (def);
       remove_phi_node (&psi, false);
 
-      /* Propagate constants immediately.  */
+      /* Propagate constants immediately, but leave an unused initialization
+        around to avoid invalidating the SCEV cache.  */
       if (CONSTANT_CLASS_P (def))
-       {
-         replace_uses_by (rslt, def);
-         release_ssa_name (rslt);
-         continue;
-       }
+       replace_uses_by (rslt, def);
 
       /* Create the replacement statements.  */
       gimple_seq stmts;
-- 
2.35.3