[gcc r12-1432] tree-optimization/100934 - properly mark irreducible regions for DOM

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

https://gcc.gnu.org/g:788bb7edb3975b80c4cb16323e7a5e55a2471e46

commit r12-1432-g788bb7edb3975b80c4cb16323e7a5e55a2471e46
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Jun 14 14:57:26 2021 +0200

    tree-optimization/100934 - properly mark irreducible regions for DOM
    
    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.
    
    2021-06-14  Richard Biener  <rguenther@suse.de>
    
            PR tree-optimization/100934
            * tree-ssa-dom.c (pass_dominator::execute): Properly
            mark irreducible regions.
    
            * gcc.dg/torture/pr100934.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/torture/pr100934.c | 21 +++++++++++++++++++++
 gcc/tree-ssa-dom.c                      |  3 ++-
 2 files changed, 23 insertions(+), 1 deletion(-)

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