[PATCH] PR tree-optimization/109417 - Check if dependency is valid before using in may_recompute_p.

[Andrew MacLeod <amacleod@redhat.com>]

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When a statement is first processed, any SSA_NAMEs that are dependencies 
are cached for quick future access.

if we ;later rewrite the statement (say propagate a constant into it), 
its possible the ssa-name in this cache is no longer active.   Normally 
this is not a problem, but the changed to may_recompute_p forgot to take 
that into account, and was checking a dependency from the cache that was 
in the SSA_NAME_FREE_LIST. It thus had no SSA_NAME_DEF_STMT when we were 
expecting one.

This patch simply rejects dependencies from consideration if they are in 
the free list.

Bootstrapping on x86_64-pc-linux-gnu  and presuming no regressio0ns, OK 
for trunk?

Andrew

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commit ecd86e159e8499feb387bc4d99bd37a5fd6a0d68
Author: Andrew MacLeod <amacleod@redhat.com>
Date:   Wed Apr 5 15:59:38 2023 -0400

    Check if dependency is valid before using in may_recompute_p.
    
    When the IL is rewritten after a statement has been processed and
    dependencies cached, its possible that an ssa-name in the dependency
    cache is no longer in the IL.  Check this before trying to recompute.
    
            PR tree-optimization/109417
            gcc/
            * gimple-range-gori.cc (gori_compute::may_recompute_p): Check if
            dependency is in SSA_NAME_FREE_LIST.
    
            gcc/testsuite/
            * gcc.dg/pr109417.c: New.

diff --git a/gcc/gimple-range-gori.cc b/gcc/gimple-range-gori.cc
index 5f4313b27dd..6e2f9533038 100644
--- a/gcc/gimple-range-gori.cc
+++ b/gcc/gimple-range-gori.cc
@@ -1314,7 +1314,9 @@ gori_compute::may_recompute_p (tree name, basic_block bb, int depth)
   tree dep2 = depend2 (name);
 
   // If the first dependency is not set, there is no recomputation.
-  if (!dep1)
+  // Dependencies reflect original IL, not current state.   Check if the
+  // SSA_NAME is still valid as well.
+  if (!dep1 || SSA_NAME_IN_FREE_LIST (dep1))
     return false;
 
   // Don't recalculate PHIs or statements with side_effects.
diff --git a/gcc/testsuite/gcc.dg/pr109417.c b/gcc/testsuite/gcc.dg/pr109417.c
new file mode 100644
index 00000000000..15711dbbafe
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr109417.c
@@ -0,0 +1,24 @@
+/* { dg-do compile } */
+/* { dg-options "-O3" } */
+
+int printf(const char *, ...);
+int c, d, *e, f[1][2], g;
+int main() {
+  int h = 0, *a = &h, **b[1] = {&a};
+  while (e)
+    while (g) {
+    L:
+      for (h = 0; h < 2; h++) {
+        while (d)
+          for (*e = 0; *e < 1;)
+            printf("0");
+        while (c)
+          ;
+        f[g][h] = 0;
+      }
+    }
+  if (h)
+    goto L;
+  return 0;
+}
+