[gcc r13-1505] tree-optimization/106198 - CFG cleanup vs LC SSA

[gcc r13-1505] tree-optimization/106198 - CFG cleanup vs LC SSA

[Richard Biener]

https://gcc.gnu.org/g:07dd0f7ba27d1fe9f0ce5b049ac5735dc5d361ad

commit r13-1505-g07dd0f7ba27d1fe9f0ce5b049ac5735dc5d361ad
Author: Richard Biener <rguenther@suse.de>
Date:   Tue Jul 5 14:14:49 2022 +0200

    tree-optimization/106198 - CFG cleanup vs LC SSA
    
    This is another case like PR106182 where for the 2nd testcase in
    the bug there are no removed or discovered loops but still changing
    loop exits invalidates LC SSA and it is not enough to just scan for
    uses in the blocks that changed loop depth.  One might argue that
    if we'd include former exit destinations we'd pick up the original
    LC SSA use but for virtuals on block merging we'd have propagated
    those out (while for regular uses we insert copies).  CFG cleanup
    can also be entered with loops needing fixup so any heuristics
    based on loop structure are bound to fail.
    
            PR tree-optimization/106198
            * tree-cfgcleanup.cc (repair_loop_structures): Always do a
            full LC SSA rewrite but only if any blocks changed loop
            depth.
    
            * gcc.dg/pr106198.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/pr106198.c | 22 ++++++++++++++++++++++
 gcc/tree-cfgcleanup.cc          |  6 +++---
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/pr106198.c b/gcc/testsuite/gcc.dg/pr106198.c
new file mode 100644
index 00000000000..00d2758efa7
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr106198.c
@@ -0,0 +1,22 @@
+/* { dg-do compile } */
+/* { dg-options "-O3" } */
+
+int printf(const char *, ...);
+long a;
+int b;
+volatile int c;
+int main() {
+  long e = a;
+  int f = a;
+ L:
+  if (b > 0) {
+    printf("0");
+    goto L;
+  }
+  if (f) {
+    printf("%ld", (long)b);
+    goto L;
+  }
+  e >= b && c;
+  return 0;
+}
diff --git a/gcc/tree-cfgcleanup.cc b/gcc/tree-cfgcleanup.cc
index 3b24e021b6b..b9ff6896ce6 100644
--- a/gcc/tree-cfgcleanup.cc
+++ b/gcc/tree-cfgcleanup.cc
@@ -1183,9 +1183,9 @@ repair_loop_structures (void)
      become unreachable by back edges from latch).  Also a former
      irreducible loop can become reducible - in this case force a full
      rewrite into loop-closed SSA form.  */
-  if (loops_state_satisfies_p (LOOP_CLOSED_SSA))
-    rewrite_into_loop_closed_ssa (n_new_or_deleted_loops ? NULL : changed_bbs,
-				  TODO_update_ssa);
+  if (loops_state_satisfies_p (LOOP_CLOSED_SSA)
+      && (!bitmap_empty_p (changed_bbs) || n_new_or_deleted_loops))
+    rewrite_into_loop_closed_ssa (NULL, TODO_update_ssa);
 
   BITMAP_FREE (changed_bbs);