From: Tamar Christina <tamar.christina@arm.com>
Date: Wed, 3 Dec 2025 14:10:36 +0000 (+0000)
Subject: vect: fix ICE when duplicate dummy IV PHIs are still in CFG [PR122969]
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=9d775818e30e73c28ef5743ca8b6ed4ae8ef1383;p=thirdparty%2Fgcc.git

vect: fix ICE when duplicate dummy IV PHIs are still in CFG [PR122969]

All the no-options result in duplicate PHI nodes that use the same values just
have different RHS

>>> p debug (loop->header)

    <bb 21> [local count: 958878292]:
    # a.2_29 = PHI <0(18), _34(25)>
    # a_lsm.8_31 = PHI <0(18), _34(25)>
    _34 = a.2_29 + -1;
    if (_34 != 1)
      goto <bb 25>; [94.50%]
    else
      goto <bb 32>; [5.50%]

    $11 = void

>>> p debug (update_bb)

    <bb 33> [local count: 958878292]:
    # a.2_6 = PHI <a_lsm.8_36(32), _41(34)>
    # a_lsm.8_18 = PHI <a_lsm.8_36(32), _41(34)>
    _41 = a.2_6 + -1;
    if (_41 != 1)
      goto <bb 34>; [94.50%]
    else
      goto <bb 26>; [5.50%]

    $12 = void

So one of the PHIs is completely useless. But that makes the update loop visit
the PHI twice, but the first time we already updated them so we end up with a
non-SSA_NAME there.

In the old code we'd just re-update the PHI with the same statement. So I've put
back that code as fallback.  I'm almost 100% sure you can't get here with any
divergent PHI as an inviant has to be a variable before we rewrite it.  But as
I'm not 100% sure I've put the update fallback instead of skipping the update.

gcc/ChangeLog:

	PR tree-optimization/122969
	* tree-vect-loop-manip.cc (vect_update_ivs_after_vectorizer): handle
	non-ssa name IV var args.

gcc/testsuite/ChangeLog:

	PR tree-optimization/122969
	* gcc.dg/vect/pr122969.c: New test.
---

diff --git a/gcc/testsuite/gcc.dg/vect/pr122969.c b/gcc/testsuite/gcc.dg/vect/pr122969.c
new file mode 100644
index 00000000000..47699fd0a1d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr122969.c
@@ -0,0 +1,16 @@
+/* { dg-add-options vect_early_break } */
+/* { dg-require-effective-target vect_early_break } */
+/* { dg-require-effective-target vect_int } */
+/* { dg-additional-options "-w -O3 -fno-tree-dominator-opts -fno-code-hoisting -fno-tree-pre -fno-tree-dce" } */
+
+/* { dg-final { scan-tree-dump "loop vectorized" "vect" } } */
+
+int a, b;
+int main() {
+  while (a)
+    for (a = 0; a != 1; a--)
+      if (b)
+        break;
+  return 0;
+}
+
diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
index 18af6a1811a..cdcfc8d0015 100644
--- a/gcc/tree-vect-loop-manip.cc
+++ b/gcc/tree-vect-loop-manip.cc
@@ -2439,10 +2439,15 @@ vect_update_ivs_after_vectorizer (loop_vec_info loop_vinfo,
       gimple *use_stmt;
       use_operand_p use_p;
       tree ic_var = PHI_ARG_DEF_FROM_EDGE (phi1, update_e);
-      FOR_EACH_IMM_USE_STMT (use_stmt, imm_iter, ic_var)
-	if (!flow_bb_inside_loop_p (loop, gimple_bb (use_stmt)))
-	  FOR_EACH_IMM_USE_ON_STMT (use_p, imm_iter)
-	    SET_USE (use_p, ni_name);
+      if (TREE_CODE (ic_var) == SSA_NAME)
+	{
+	  FOR_EACH_IMM_USE_STMT (use_stmt, imm_iter, ic_var)
+	    if (!flow_bb_inside_loop_p (loop, gimple_bb (use_stmt)))
+	      FOR_EACH_IMM_USE_ON_STMT (use_p, imm_iter)
+		SET_USE (use_p, ni_name);
+	}
+      else
+	adjust_phi_and_debug_stmts (phi1, update_e, ni_name);
     }
 }