[gcc r9-9769] tree-optimization/100934 - properly mark irreducible regions for DOM

[Richard Biener]

https://gcc.gnu.org/g:e89b09601907f3f3ba6c988ebef7b978af40b83a

commit r9-9769-ge89b09601907f3f3ba6c988ebef7b978af40b83a
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.
    
    (cherry picked from commit 788bb7edb3975b80c4cb16323e7a5e55a2471e46)

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 b0d56fcf3e3..5bb337b5417 100644
--- a/gcc/tree-ssa-dom.c
+++ b/gcc/tree-ssa-dom.c
@@ -695,7 +695,8 @@ 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);
 
   /* Initialize the value-handle array.  */
   threadedge_initialize_values ();