[gcc r10-9924] tree-optimization/100934 - properly mark irreducible regions for DOM

[Richard Biener]

https://gcc.gnu.org/g:b7878d4e179c72ad69cdd103fbbfe16bc38010db

commit r10-9924-gb7878d4e179c72ad69cdd103fbbfe16bc38010db
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 864c984f636..c0d77b5f46c 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 ();