Index: lib/Target/AMDGPU/SIInstrInfo.cpp
===================================================================
--- lib/Target/AMDGPU/SIInstrInfo.cpp
+++ lib/Target/AMDGPU/SIInstrInfo.cpp
@@ -584,6 +584,12 @@
   if (RI.isSGPRClass(RC)) {
     MFI->setHasSpilledSGPRs();
 
+    if (RC->getSize() == 4) {
+      // m0 may not be allowed for readlane.
+      MachineRegisterInfo &MRI = MF->getRegInfo();
+      MRI.constrainRegClass(SrcReg, &AMDGPU::SReg_32_XM0RegClass);
+    }
+
     // We are only allowed to create one new instruction when spilling
     // registers, so we need to use pseudo instruction for spilling
     // SGPRs.
@@ -677,6 +683,13 @@
     // FIXME: Maybe this should not include a memoperand because it will be
     // lowered to non-memory instructions.
     unsigned Opcode = getSGPRSpillRestoreOpcode(RC->getSize());
+
+    if (RC->getSize() == 4) {
+      // m0 may not be allowed for readlane.
+      MachineRegisterInfo &MRI = MF->getRegInfo();
+      MRI.constrainRegClass(DestReg, &AMDGPU::SReg_32_XM0RegClass);
+    }
+
     BuildMI(MBB, MI, DL, get(Opcode), DestReg)
       .addFrameIndex(FrameIndex) // frame_idx
       .addMemOperand(MMO);
Index: test/CodeGen/AMDGPU/si-sgpr-spill.ll
===================================================================
--- test/CodeGen/AMDGPU/si-sgpr-spill.ll
+++ test/CodeGen/AMDGPU/si-sgpr-spill.ll
@@ -1,5 +1,5 @@
-; RUN: llc -march=amdgcn -mcpu=SI < %s | FileCheck %s
-; RUN: llc -march=amdgcn -mcpu=tonga < %s | FileCheck %s
+; RUN: llc -march=amdgcn -verify-machineinstrs < %s | FileCheck %s
+; RUN: llc -march=amdgcn -mcpu=tonga -verify-machineinstrs < %s | FileCheck %s
 
 ; These tests check that the compiler won't crash when it needs to spill
 ; SGPRs.