From: Richard Biener <rguenther@suse.de>
Date: Wed, 21 Aug 2024 11:56:40 +0000 (+0200)
Subject: tree-optimization/116380 - bogus SSA update with loop distribution
X-Git-Tag: basepoints/gcc-16~6484
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=af0d2d95a5f767d92bd64f959679fb4612247b0b;p=thirdparty%2Fgcc.git

tree-optimization/116380 - bogus SSA update with loop distribution

When updating LC PHIs after copying loops we have to handle defs
defined outside of the loop appropriately (by not setting them to
NULL ...).  This mimics how we handle this in the SSA updating
code of the vectorizer.

	PR tree-optimization/116380
	* tree-loop-distribution.cc (copy_loop_before): Handle
	out-of-loop defs appropriately.

	* gcc.dg/torture/pr116380.c: New testcase.
---

diff --git a/gcc/testsuite/gcc.dg/torture/pr116380.c b/gcc/testsuite/gcc.dg/torture/pr116380.c
new file mode 100644
index 00000000000..5ffd99459d2
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr116380.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-fno-tree-scev-cprop" } */
+
+int a[3], d[3], c;
+int f(int e, int b)
+{
+  for (; e < 3; e++)
+    {
+      a[0] = 0;
+      if (b)
+	c = b;
+      d[e] = 0;
+      a[e] = 0;
+    }
+  return e;
+}
diff --git a/gcc/tree-loop-distribution.cc b/gcc/tree-loop-distribution.cc
index f87393ee94d..10f261a8769 100644
--- a/gcc/tree-loop-distribution.cc
+++ b/gcc/tree-loop-distribution.cc
@@ -980,6 +980,9 @@ copy_loop_before (class loop *loop, bool redirect_lc_phi_defs)
 	  if (TREE_CODE (USE_FROM_PTR (use_p)) == SSA_NAME)
 	    {
 	      tree new_def = get_current_def (USE_FROM_PTR (use_p));
+	      if (!new_def)
+		/* Something defined outside of the loop.  */
+		continue;
 	      SET_USE (use_p, new_def);
 	    }
 	}