[gcc(refs/users/aoliva/heads/testme)] [PR105665] ivopts: check defs of names in base for undefs

[Alexandre Oliva <aoliva@gcc.gnu.org>]

https://gcc.gnu.org/g:e90f0f0296d12932b2ec3660b296328c11f73cb3

commit e90f0f0296d12932b2ec3660b296328c11f73cb3
Author: Alexandre Oliva <oliva@adacore.com>
Date:   Thu May 26 09:38:31 2022 -0300

    [PR105665] ivopts: check defs of names in base for undefs

Diff:
---
 gcc/testsuite/gcc.dg/torture/pr105665.c | 20 ++++++++++++++++++++
 gcc/tree-ssa-loop-ivopts.cc             | 24 +++++++++++++++++++++---
 2 files changed, 41 insertions(+), 3 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/torture/pr105665.c b/gcc/testsuite/gcc.dg/torture/pr105665.c
new file mode 100644
index 00000000000..12f0b78a4b4
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr105665.c
@@ -0,0 +1,20 @@
+/* { dg-do run } */
+
+int a, b, c[1], d[2], *e = c;
+int main() {
+  int f = 0;
+  for (; b < 2; b++) {
+    int g;
+    if (f)
+      b = 40;
+    a = d[b * b];
+    for (f = 0; f < 3; f++) {
+      if (e)
+        break;
+      g--;
+      if (a)
+        a = g;
+    }
+  }
+  return 0;
+}
diff --git a/gcc/tree-ssa-loop-ivopts.cc b/gcc/tree-ssa-loop-ivopts.cc
index 81b536f9304..5b1c7340f77 100644
--- a/gcc/tree-ssa-loop-ivopts.cc
+++ b/gcc/tree-ssa-loop-ivopts.cc
@@ -3076,9 +3076,27 @@ get_loop_invariant_expr (struct ivopts_data *data, tree inv_expr)
 static tree
 find_ssa_undef (tree *tp, int *walk_subtrees, void *)
 {
-  if (TREE_CODE (*tp) == SSA_NAME
-      && ssa_undefined_value_p (*tp, false))
-    return *tp;
+  if (TREE_CODE (*tp) == SSA_NAME)
+    {
+      if (ssa_undefined_value_p (*tp, false))
+	return *tp;
+
+      gimple *def_stmt = SSA_NAME_DEF_STMT (*tp);
+      /* ssa_undefined_value_p must have caught nop defs above.  */
+      gcc_checking_assert (!gimple_nop_p (def_stmt));
+
+      ssa_op_iter iter;
+      use_operand_p use_p;
+
+      FOR_EACH_PHI_OR_STMT_USE (use_p, def_stmt, iter, SSA_OP_USE)
+	{
+	  tree use = USE_FROM_PTR (use_p);
+
+	  if (ssa_undefined_value_p (use, false))
+	    return use;
+	}
+    }
+
   if (!EXPR_P (*tp))
     *walk_subtrees = 0;
   return NULL;