From a4d55a2c3607c411a16a01a61bd667a03fee7264 Mon Sep 17 00:00:00 2001
From: Simon Pilgrim <llvm-dev@redking.me.uk>
Date: Wed, 23 Oct 2019 07:33:29 -0700
Subject: [PATCH] [X86] combineX86ShufflesRecursively - assert the root mask is
 legal. NFCI.

---
 llvm/lib/Target/X86/X86ISelLowering.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index ed975e9..9e62858 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -33026,6 +33026,9 @@ static SDValue combineX86ShufflesRecursively(
     ArrayRef<int> RootMask, ArrayRef<const SDNode *> SrcNodes, unsigned Depth,
     bool HasVariableMask, bool AllowVariableMask, SelectionDAG &DAG,
     const X86Subtarget &Subtarget) {
+  assert(RootMask.size() > 0 && (RootMask.size() > 1 || RootMask[0] == 0) &&
+         "Illegal shuffle root mask");
+
   // Bound the depth of our recursive combine because this is ultimately
   // quadratic in nature.
   const unsigned MaxRecursionDepth = 8;
-- 
2.7.4