[gcc r13-9511] tree-optimization/114052 - consider infinite sub-loops when lowering iter bound

[Richard Biener]

https://gcc.gnu.org/g:2f37a08b51ef8022a2ef0b596006df65ceb44314

commit r13-9511-g2f37a08b51ef8022a2ef0b596006df65ceb44314
Author: Richard Biener <rguenther@suse.de>
Date:   Wed Jan 29 13:25:14 2025 +0100

    tree-optimization/114052 - consider infinite sub-loops when lowering iter bound
    
    When we walk stmts to find always executed stmts with UB in the last
    iteration to be able to reduce the iteration count by one we fail
    to consider infinite subloops in the last iteration that would make
    such stmt not execute.  The following adds this.
    
            PR tree-optimization/114052
            * tree-ssa-loop-niter.cc (maybe_lower_iteration_bound): Check
            for infinite subloops we might not exit.
    
            * gcc.dg/pr114052-1.c: New testcase.
    
    (cherry picked from commit d1c7837d2d6e5a2997228681166ed8c814891881)

Diff:
---
 gcc/testsuite/gcc.dg/pr114052-1.c | 40 +++++++++++++++++++++++++++++++++++++++
 gcc/tree-ssa-loop-niter.cc        |  9 ++++++++-
 2 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/gcc/testsuite/gcc.dg/pr114052-1.c b/gcc/testsuite/gcc.dg/pr114052-1.c
new file mode 100644
index 000000000000..e971f6844146
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr114052-1.c
@@ -0,0 +1,40 @@
+/* { dg-do run } */
+/* { dg-require-effective-target signal } */
+/* { dg-options "-O2" } */
+
+#include <stdint.h>
+#include <unistd.h>
+#include <signal.h>
+#include <stdlib.h>
+
+volatile int y;
+void __attribute__((noipa)) put(int x)
+{
+  if (y)
+    __builtin_printf ("%i\n", x);
+}
+
+void __attribute__((noipa)) f(void)
+{
+  int counter = 0;
+  while (1) {
+      if (counter >= 2) continue;
+      put (counter++);
+  }
+}
+
+void do_exit (int i)
+{
+  exit (0);
+}
+
+int main()
+{
+  struct sigaction s;
+  sigemptyset (&s.sa_mask);
+  s.sa_handler = do_exit;
+  s.sa_flags = 0;
+  sigaction (SIGALRM, &s, NULL);
+  alarm (1);
+  f();
+}
diff --git a/gcc/tree-ssa-loop-niter.cc b/gcc/tree-ssa-loop-niter.cc
index 878442bdeb45..4e6bd5176b6f 100644
--- a/gcc/tree-ssa-loop-niter.cc
+++ b/gcc/tree-ssa-loop-niter.cc
@@ -4680,7 +4680,14 @@ maybe_lower_iteration_bound (class loop *loop)
           FOR_EACH_EDGE (e, ei, bb->succs)
 	    {
 	      if (loop_exit_edge_p (loop, e)
-		  || e == loop_latch_edge (loop))
+		  || e == loop_latch_edge (loop)
+		  /* When exiting an inner loop, verify it is finite.  */
+		  || (!flow_bb_inside_loop_p (bb->loop_father, e->dest)
+		      && !finite_loop_p (bb->loop_father))
+		  /* When we enter an irreducible region and the entry
+		     does not contain a bounding stmt assume it might be
+		     infinite.  */
+		  || (bb->flags & BB_IRREDUCIBLE_LOOP))
 		{
 		  found_exit = true;
 		  break;