Index: lib/CodeGen/MachineInstr.cpp
===================================================================
--- lib/CodeGen/MachineInstr.cpp
+++ lib/CodeGen/MachineInstr.cpp
@@ -1309,7 +1309,7 @@
     unsigned Reg, bool isKill, const TargetRegisterInfo *TRI) const {
   for (unsigned i = 0, e = getNumOperands(); i != e; ++i) {
     const MachineOperand &MO = getOperand(i);
-    if (!MO.isReg() || !MO.isUse())
+    if (!MO.isReg() || !MO.isUse() || MO.isUndef())
       continue;
     unsigned MOReg = MO.getReg();
     if (!MOReg)
Index: test/CodeGen/X86/pr31143.ll
===================================================================
--- test/CodeGen/X86/pr31143.ll
+++ test/CodeGen/X86/pr31143.ll
@@ -0,0 +1,31 @@
+; RUN: llc --mattr=+sse4.1 %s -o - | FileCheck %s
+
+target triple = "x86_64-pc-linux-gnu"
+
+
+; CHECK:      xorps   [[XMM1:%xmm[0-9]+]], [[XMM1]]
+; CHECK-NEXT: roundss $9, [[XMM0:%xmm[0-9]+]], [[XMM1]]
+
+define void @test(float* nocapture %a, <4 x float>* nocapture %b, i32 %k) {
+entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %arrayidx = getelementptr inbounds float, float* %a, i64 %indvars.iv
+  %v = load float, float* %arrayidx, align 4
+  %floor = call float @floorf(float %v)
+  %sub = fsub float %floor, %v
+  %v1 = insertelement <4 x float> undef, float %sub, i32 0
+  %br = shufflevector <4 x float> %v1, <4 x float> undef, <4 x i32> <i32 0, i32 0, i32 0, i32 0>
+  store volatile <4 x float> %br, <4 x float>* %b, align 4
+  %indvars.iv.next = add i64 %indvars.iv, 1
+  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+  %exitcond = icmp eq i32 %lftr.wideiv, %k
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:
+  ret void
+}
+
+declare float @floorf(float) nounwind readnone