From: Richard Biener <rguenther@suse.de>
Date: Tue, 21 Apr 2026 08:21:34 +0000 (+0200)
Subject: tree-optimization/124947 - IVOPTs emits uninit use
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d84a91bbd60bfabc1cd2dac6aae10a427a770627;p=thirdparty%2Fgcc.git

tree-optimization/124947 - IVOPTs emits uninit use

The following prevents IVOPTs from rewriting a compare using an IV
that involves undefined SSA vars.

	PR tree-optimization/124947
	* tree-ssa-loop-ivopts.cc (may_eliminate_iv): Do not use
	a candidate that involves undefs.

	* gcc.dg/pr124947.c: New testcase.
---

diff --git a/gcc/testsuite/gcc.dg/pr124947.c b/gcc/testsuite/gcc.dg/pr124947.c
new file mode 100644
index 00000000000..5e64d29a943
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr124947.c
@@ -0,0 +1,19 @@
+/* { dg-options "-O -fdump-tree-ivopts" } */
+
+long *BN_uadd_ap;
+
+void
+BN_uadd (int dif, long t1)
+{
+  volatile long *rp;
+  while (dif)
+    {
+      dif--;
+      t1 = *BN_uadd_ap;
+      *rp++ = t1;
+      if (t1)
+        break;
+    }
+}
+
+/* { dg-final { scan-tree-dump-times "rp_\[0-9\]+\\\(D\\\)" 1 "ivopts" } } */
diff --git a/gcc/tree-ssa-loop-ivopts.cc b/gcc/tree-ssa-loop-ivopts.cc
index 6ecf5bef7b4..dfec607fd2e 100644
--- a/gcc/tree-ssa-loop-ivopts.cc
+++ b/gcc/tree-ssa-loop-ivopts.cc
@@ -5382,6 +5382,11 @@ may_eliminate_iv (struct ivopts_data *data,
   aff_tree bnd;
   class tree_niter_desc *desc = NULL;
 
+  /* If the IV candidate involves undefs do not attempt to use it to
+     express a condition.  */
+  if (cand->involves_undefs)
+    return false;
+
   if (TREE_CODE (cand->iv->step) != INTEGER_CST)
     return false;