[gcc r12-9723] tree-optimization/110298 - CFG cleanup and stale nb_iterations

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

https://gcc.gnu.org/g:c409f2a1cc5d5bffe2fb93454924ae402c57f8f6

commit r12-9723-gc409f2a1cc5d5bffe2fb93454924ae402c57f8f6
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Jun 19 09:52:45 2023 +0200

    tree-optimization/110298 - CFG cleanup and stale nb_iterations
    
    When unrolling we eventually kill nb_iterations info since it may
    refer to removed SSA names.  But we do this only after cleaning
    up the CFG which in turn can end up accessing it.  Fixed by
    swapping the two.
    
            PR tree-optimization/110298
            * tree-ssa-loop-ivcanon.cc (tree_unroll_loops_completely):
            Clear number of iterations info before cleaning up the CFG.
    
            * gcc.dg/torture/pr110298.c: New testcase.
    
    (cherry picked from commit 916add3bf6e46467e4391e358b11ecfbc4daa275)

Diff:
---
 gcc/testsuite/gcc.dg/torture/pr110298.c | 20 ++++++++++++++++++++
 gcc/tree-ssa-loop-ivcanon.cc            |  7 ++++---
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/torture/pr110298.c b/gcc/testsuite/gcc.dg/torture/pr110298.c
new file mode 100644
index 00000000000..139f5c77d89
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr110298.c
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+
+int a, b, c, d, e;
+int f() {
+  c = 0;
+  for (; c >= 0; c--) {
+    d = 0;
+    for (; d <= 0; d++) {
+      e = 0;
+      for (; d + c + e >= 0; e--)
+        ;
+      a = 1;
+      b = 0;
+      for (; a; ++b)
+        a *= 2;
+      for (; b + d >= 0;)
+        return 0;
+    }
+  }
+}
diff --git a/gcc/tree-ssa-loop-ivcanon.cc b/gcc/tree-ssa-loop-ivcanon.cc
index e2ac2044741..408916c7de0 100644
--- a/gcc/tree-ssa-loop-ivcanon.cc
+++ b/gcc/tree-ssa-loop-ivcanon.cc
@@ -1487,15 +1487,16 @@ tree_unroll_loops_completely (bool may_increase_size, bool unroll_outer)
 	    }
 	  BITMAP_FREE (fathers);
 
+	  /* Clean up the information about numbers of iterations, since
+	     complete unrolling might have invalidated it.  */
+	  scev_reset ();
+
 	  /* This will take care of removing completely unrolled loops
 	     from the loop structures so we can continue unrolling now
 	     innermost loops.  */
 	  if (cleanup_tree_cfg ())
 	    update_ssa (TODO_update_ssa_only_virtuals);
 
-	  /* Clean up the information about numbers of iterations, since
-	     complete unrolling might have invalidated it.  */
-	  scev_reset ();
 	  if (flag_checking && loops_state_satisfies_p (LOOP_CLOSED_SSA))
 	    verify_loop_closed_ssa (true);
 	}