[PATCH] tree-optimization/100934 - properly mark irreducible regions for DOM

[Richard Biener]

The jump threading code requires marked irreducible regions for the
purpose of validating jump threading paths but DOM fails to provide
that resulting in mised number of iteration upper bounds clearing.

Bootstrap / regtest running on x86_64-unknown-linux-gnu.

2021-06-14  Richard Biener  <rguent...@suse.de>

        PR tree-optimization/100934
        * tree-ssa-dom.c (pass_dominator::execute): Properly
        mark irreducible regions.

        * gcc.dg/torture/pr100934.c: New testcase.
---
 gcc/testsuite/gcc.dg/torture/pr100934.c | 21 +++++++++++++++++++++
 gcc/tree-ssa-dom.c                      |  3 ++-
 2 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.dg/torture/pr100934.c

diff --git a/gcc/testsuite/gcc.dg/torture/pr100934.c 
b/gcc/testsuite/gcc.dg/torture/pr100934.c
new file mode 100644
index 00000000000..43b78849895
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr100934.c
@@ -0,0 +1,21 @@
+/* { dg-do run } */
+
+int a, b, c, d, e;
+int main()
+{
+  int f = 0, g = 0;
+  for (; f < 2; f++)
+    {
+      int h, i;
+      for (h = 0; h < 2; h++)
+       {
+         b = e = g ? a % g : 0;
+         c = d;
+         for (i = 0; i < 1; i++)
+           g = 0;
+         for (; g < 2; g++)
+           ;
+       }
+    }
+  return 0;
+}
diff --git a/gcc/tree-ssa-dom.c b/gcc/tree-ssa-dom.c
index 075b1ccb9de..c231e6c8467 100644
--- a/gcc/tree-ssa-dom.c
+++ b/gcc/tree-ssa-dom.c
@@ -727,7 +727,8 @@ pass_dominator::execute (function *fun)
      gcc.dg/tree-ssa/pr21417.c can't be threaded if loop preheader is
      missing.  We should improve jump threading in future then
      LOOPS_HAVE_PREHEADERS won't be needed here.  */
-  loop_optimizer_init (LOOPS_HAVE_PREHEADERS | LOOPS_HAVE_SIMPLE_LATCHES);
+  loop_optimizer_init (LOOPS_HAVE_PREHEADERS | LOOPS_HAVE_SIMPLE_LATCHES
+                      | LOOPS_HAVE_MARKED_IRREDUCIBLE_REGIONS);
 
   /* We need accurate information regarding back edges in the CFG
      for jump threading; this may include back edges that are not part of
-- 
2.26.2