1 files changed, 8 insertions, 4 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/InstrEmitter.cpp b/llvm/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
index 5ec10308dc2..5268da2ff4f 100644
--- a/llvm/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
@@ -330,11 +330,15 @@ InstrEmitter::AddRegisterOperand(MachineInstrBuilder &MIB,
   // shrink VReg's register class within reason.  For example, if VReg == GR32
   // and II requires a GR32_NOSP, just constrain VReg to GR32_NOSP.
   if (II) {
-    const TargetRegisterClass *DstRC = nullptr;
+    const TargetRegisterClass *OpRC = nullptr;
     if (IIOpNum < II->getNumOperands())
-      DstRC = TRI->getAllocatableClass(TII->getRegClass(*II,IIOpNum,TRI,*MF));
-    if (DstRC && !MRI->constrainRegClass(VReg, DstRC, MinRCSize)) {
-      unsigned NewVReg = MRI->createVirtualRegister(DstRC);
+      OpRC = TII->getRegClass(*II, IIOpNum, TRI, *MF);
+
+    if (OpRC && !MRI->constrainRegClass(VReg, OpRC, MinRCSize)) {
+      assert(OpRC->isAllocatable() &&
+           "Constraining an allocatable VReg produced an unallocatable class?");
+
+      unsigned NewVReg = MRI->createVirtualRegister(OpRC);
       BuildMI(*MBB, InsertPos, Op.getNode()->getDebugLoc(),
               TII->get(TargetOpcode::COPY), NewVReg).addReg(VReg);
       VReg = NewVReg;