[PATCH] tree-optimization/109327 - forwprop stmt removal issue

[Richard Biener via Gcc-patches]

There's interfering between the to_removed queue and other mechanisms
removing stmts, in this case remove_prop_source_from_use.  The following
makes the to_remove queue draining more permissive.

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

        PR tree-optimization/109327
        * tree-ssa-forwprop.cc (pass_forwprop::execute): Deal with
        already removed stmts when draining to_remove.

        * gcc.dg/pr109327.c: New testcase.
---
 gcc/testsuite/gcc.dg/pr109327.c | 15 +++++++++++++++
 gcc/tree-ssa-forwprop.cc        |  4 ++++
 2 files changed, 19 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/pr109327.c

diff --git a/gcc/testsuite/gcc.dg/pr109327.c b/gcc/testsuite/gcc.dg/pr109327.c
new file mode 100644
index 00000000000..827b26f148e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr109327.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fno-tree-ccp" } */
+
+int a;
+void b(int c) {}
+int main()
+{
+  int d = 0, *e = &a;
+  if (d) {
+    int *f = e;
+    while (a)
+      b(e != f);
+  }
+  return 0;
+}
diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
index 5eccc7a89b5..bb0fa306312 100644
--- a/gcc/tree-ssa-forwprop.cc
+++ b/gcc/tree-ssa-forwprop.cc
@@ -4061,6 +4061,10 @@ pass_forwprop::execute (function *fun)
   while (!to_remove.is_empty())
     {
       gimple *stmt = to_remove.pop ();
+      /* For example remove_prop_source_from_use can remove stmts queued
+        for removal.  Deal with this gracefully.  */
+      if (!gimple_bb (stmt))
+       continue;
       if (dump_file && (dump_flags & TDF_DETAILS))
        {
          fprintf (dump_file, "Removing dead stmt ");
-- 
2.35.3