[gcc r13-6850] Ranger cache dominator queries should ignore backedges.

[gcc r13-6850] Ranger cache dominator queries should ignore backedges.

[Andrew Macleod]

https://gcc.gnu.org/g:0409aa5a2de9ce3164933814a4a7adc91f6acb96

commit r13-6850-g0409aa5a2de9ce3164933814a4a7adc91f6acb96
Author: Andrew MacLeod <amacleod@redhat.com>
Date:   Thu Mar 23 10:28:34 2023 -0400

    Ranger cache dominator queries should ignore backedges.
    
    When querying dominators for cache values, ignore back edges in
    read-only mode.
    
            PR tree-optimization/109238
            gcc/
            * gimple-range-cache.cc (ranger_cache::resolve_dom): Ignore
            predecessors which this block dominates.
    
            gcc/testsuite/
            * gcc.dg/pr109238.c: New.

Diff:
---
 gcc/gimple-range-cache.cc       |  5 +++++
 gcc/testsuite/gcc.dg/pr109238.c | 16 ++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/gcc/gimple-range-cache.cc b/gcc/gimple-range-cache.cc
index cc56fd4dcb0..6a098d8ec28 100644
--- a/gcc/gimple-range-cache.cc
+++ b/gcc/gimple-range-cache.cc
@@ -1404,6 +1404,11 @@ ranger_cache::resolve_dom (vrange &r, tree name, basic_block bb)
   Value_Range er (TREE_TYPE (name));
   FOR_EACH_EDGE (e, ei, bb->preds)
     {
+      // If the predecessor is dominated by this block, then there is a back
+      // edge, and won't provide anything useful.  We'll actually end up with
+      // VARYING as we will not resolve this node.
+      if (dominated_by_p (CDI_DOMINATORS, e->src, bb))
+	continue;
       edge_range (er, e, name, RFD_READ_ONLY);
       r.union_ (er);
     }
diff --git a/gcc/testsuite/gcc.dg/pr109238.c b/gcc/testsuite/gcc.dg/pr109238.c
new file mode 100644
index 00000000000..0cad8237208
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr109238.c
@@ -0,0 +1,16 @@
+/* PR tree-optimization/109238 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wall" } */
+
+void foo (void *) __attribute__((noreturn));
+void bar (void *);
+
+void
+baz (void *p)
+{
+  void *c = __builtin_realloc (p, 16);
+  if (c)
+    foo (c);
+  for (;;)
+    bar (__builtin_realloc (p, 8));	/* { dg-bogus "pointer 'p' may be used after '__builtin_realloc'" } */
+}