Index: lib/Target/AMDGPU/AMDGPURegisterBankInfo.h
===================================================================
--- lib/Target/AMDGPU/AMDGPURegisterBankInfo.h
+++ lib/Target/AMDGPU/AMDGPURegisterBankInfo.h
@@ -41,6 +41,9 @@
                               MachineRegisterInfo &MRI,
                               ArrayRef<unsigned> OpIndices) const;
 
+  void constrainOpWithReadfirstlane(MachineInstr &MI, MachineRegisterInfo &MRI,
+                                    unsigned OpIdx) const;
+
   /// See RegisterBankInfo::applyMapping.
   void applyMappingImpl(const OperandsMapper &OpdMapper) const override;
 
@@ -70,6 +73,10 @@
                       const std::array<unsigned, NumOps> RegSrcOpIdx,
                       ArrayRef<OpRegBankEntry<NumOps>> Table) const;
 
+  RegisterBankInfo::InstructionMappings
+  getInstrAlternativeMappingsIntrinsic(
+      const MachineInstr &MI, const MachineRegisterInfo &MRI) const;
+
   RegisterBankInfo::InstructionMappings
   getInstrAlternativeMappingsIntrinsicWSideEffects(
       const MachineInstr &MI, const MachineRegisterInfo &MRI) const;
Index: lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp
===================================================================
--- lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp
+++ lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp
@@ -142,6 +142,28 @@
   return AltMappings;
 }
 
+RegisterBankInfo::InstructionMappings
+AMDGPURegisterBankInfo::getInstrAlternativeMappingsIntrinsic(
+    const MachineInstr &MI, const MachineRegisterInfo &MRI) const {
+  switch (MI.getOperand(MI.getNumExplicitDefs()).getIntrinsicID()) {
+  case Intrinsic::amdgcn_readlane: {
+    static const OpRegBankEntry<3> Table[2] = {
+      // Perfectly legal.
+      { { AMDGPU::SGPRRegBankID, AMDGPU::VGPRRegBankID, AMDGPU::SGPRRegBankID }, 1 },
+
+      // Need a readfirstlane for the index.
+      { { AMDGPU::SGPRRegBankID, AMDGPU::VGPRRegBankID, AMDGPU::VGPRRegBankID }, 2 }
+    };
+
+    const std::array<unsigned, 3> RegSrcOpIdx = { { 0, 2, 3 } };
+    return addMappingFromTable<3>(MI, MRI, RegSrcOpIdx, makeArrayRef(Table));
+  }
+
+  default:
+    return RegisterBankInfo::getInstrAlternativeMappings(MI);
+  }
+}
+
 RegisterBankInfo::InstructionMappings
 AMDGPURegisterBankInfo::getInstrAlternativeMappingsIntrinsicWSideEffects(
     const MachineInstr &MI, const MachineRegisterInfo &MRI) const {
@@ -365,6 +387,8 @@
     AltMappings.push_back(&VMapping);
     return AltMappings;
   }
+  case AMDGPU::G_INTRINSIC:
+    return getInstrAlternativeMappingsIntrinsic(MI, MRI);
   case AMDGPU::G_INTRINSIC_W_SIDE_EFFECTS:
     return getInstrAlternativeMappingsIntrinsicWSideEffects(MI, MRI);
   default:
@@ -718,6 +742,28 @@
     .addReg(SaveExecReg);
 }
 
+// Legalize an operand that must be an SGPR by inserting a readfirstlane.
+void AMDGPURegisterBankInfo::constrainOpWithReadfirstlane(
+    MachineInstr &MI, MachineRegisterInfo &MRI, unsigned OpIdx) const {
+  unsigned Reg = MI.getOperand(OpIdx).getReg();
+  const RegisterBank *Bank = getRegBank(Reg, MRI, *TRI);
+  if (Bank != &AMDGPU::VGPRRegBank)
+    return;
+
+  MachineIRBuilder B(MI);
+  unsigned SGPR = MRI.createVirtualRegister(&AMDGPU::SReg_32_XM0RegClass);
+  B.buildInstr(AMDGPU::V_READFIRSTLANE_B32)
+    .addDef(SGPR)
+    .addReg(Reg);
+
+  const TargetRegisterClass *Constrained =
+      constrainGenericRegister(Reg, AMDGPU::VGPR_32RegClass, MRI);
+  (void)Constrained;
+  assert(Constrained && "Failed to constrain readfirstlane src reg");
+
+  MI.getOperand(OpIdx).setReg(SGPR);
+}
+
 void AMDGPURegisterBankInfo::applyMappingImpl(
     const OperandsMapper &OpdMapper) const {
   MachineInstr &MI = OpdMapper.getMI();
@@ -894,6 +940,27 @@
     executeInWaterfallLoop(MI, MRI, { 2 });
     return;
 
+  case AMDGPU::G_INTRINSIC: {
+    switch (MI.getOperand(MI.getNumExplicitDefs()).getIntrinsicID()) {
+    case Intrinsic::amdgcn_readlane: {
+      SmallVector<unsigned, 1> SrcReg(OpdMapper.getVRegs(2));
+
+      if (!SrcReg.empty()) {
+        assert(SrcReg.size() == 1);
+        MI.getOperand(2).setReg(SrcReg[0]);
+      }
+
+      assert(empty(OpdMapper.getVRegs(0)));
+      assert(empty(OpdMapper.getVRegs(3)));
+
+      constrainOpWithReadfirstlane(MI, MRI, 3); // Index
+      return;
+    }
+    default:
+      break;
+    }
+    break;
+  }
   case AMDGPU::G_INTRINSIC_W_SIDE_EFFECTS: {
     switch (MI.getOperand(MI.getNumExplicitDefs()).getIntrinsicID()) {
     case Intrinsic::amdgcn_buffer_load: {
@@ -1437,6 +1504,21 @@
                                                SrcSize);
       break;
     }
+    case Intrinsic::amdgcn_readlane: {
+      // This must be an SGPR, but accept a VGPR.
+      unsigned IdxReg = MI.getOperand(3).getReg();
+      unsigned IdxSize = MRI.getType(IdxReg).getSizeInBits();
+      unsigned IdxBank = getRegBankID(IdxReg, MRI, *TRI, AMDGPU::SGPRRegBankID);
+      OpdsMapping[3] = AMDGPU::getValueMapping(IdxBank, IdxSize);
+      LLVM_FALLTHROUGH;
+    }
+    case Intrinsic::amdgcn_readfirstlane: {
+      unsigned DstSize = MRI.getType(MI.getOperand(0).getReg()).getSizeInBits();
+      unsigned SrcSize = MRI.getType(MI.getOperand(2).getReg()).getSizeInBits();
+      OpdsMapping[0] = AMDGPU::getValueMapping(AMDGPU::SGPRRegBankID, DstSize);
+      OpdsMapping[2] = AMDGPU::getValueMapping(AMDGPU::VGPRRegBankID, SrcSize);
+      break;
+    }
     }
     break;
   }
Index: test/CodeGen/AMDGPU/GlobalISel/regbankselect-amdgcn.readfirstlane.mir
===================================================================
--- /dev/null
+++ test/CodeGen/AMDGPU/GlobalISel/regbankselect-amdgcn.readfirstlane.mir
@@ -0,0 +1,32 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -march=amdgcn -mcpu=fiji -run-pass=regbankselect -regbankselect-fast -verify-machineinstrs -o - %s | FileCheck %s
+# RUN: llc -march=amdgcn -mcpu=fiji -run-pass=regbankselect -regbankselect-greedy -verify-machineinstrs -o - %s | FileCheck %s
+
+---
+name: readfirstlane_s
+legalized: true
+
+body: |
+  bb.0:
+    liveins: $sgpr0
+    ; CHECK-LABEL: name: readfirstlane_s
+    ; CHECK: [[COPY:%[0-9]+]]:sgpr(s32) = COPY $sgpr0
+    ; CHECK: [[COPY1:%[0-9]+]]:vgpr(s32) = COPY [[COPY]](s32)
+    ; CHECK: [[INT:%[0-9]+]]:sgpr(s32) = G_INTRINSIC intrinsic(@llvm.amdgcn.readfirstlane), [[COPY1]](s32)
+    %0:_(s32) = COPY $sgpr0
+    %1:_(s32) = G_INTRINSIC intrinsic(@llvm.amdgcn.readfirstlane), %0
+...
+
+---
+name: readfirstlane_v
+legalized: true
+
+body: |
+  bb.0:
+    liveins: $vgpr0
+    ; CHECK-LABEL: name: readfirstlane_v
+    ; CHECK: [[COPY:%[0-9]+]]:vgpr(s32) = COPY $vgpr0
+    ; CHECK: [[INT:%[0-9]+]]:sgpr(s32) = G_INTRINSIC intrinsic(@llvm.amdgcn.readfirstlane), [[COPY]](s32)
+    %0:_(s32) = COPY $vgpr0
+    %1:_(s32) = G_INTRINSIC intrinsic(@llvm.amdgcn.readfirstlane), %0
+...
Index: test/CodeGen/AMDGPU/GlobalISel/regbankselect-amdgcn.readlane.mir
===================================================================
--- /dev/null
+++ test/CodeGen/AMDGPU/GlobalISel/regbankselect-amdgcn.readlane.mir
@@ -0,0 +1,71 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -march=amdgcn -mcpu=fiji -run-pass=regbankselect %s -verify-machineinstrs -o - -regbankselect-fast | FileCheck %s
+# RUN: llc -march=amdgcn -mcpu=fiji -run-pass=regbankselect %s -verify-machineinstrs -o - -regbankselect-greedy | FileCheck %s
+
+---
+name: readlane_ss
+legalized: true
+
+body: |
+  bb.0:
+    liveins: $sgpr0, $sgpr1
+    ; CHECK-LABEL: name: readlane_ss
+    ; CHECK: [[COPY:%[0-9]+]]:sgpr(s32) = COPY $sgpr0
+    ; CHECK: [[COPY1:%[0-9]+]]:sgpr(s32) = COPY $sgpr1
+    ; CHECK: [[COPY2:%[0-9]+]]:vgpr(s32) = COPY [[COPY]](s32)
+    ; CHECK: [[INT:%[0-9]+]]:sgpr(s32) = G_INTRINSIC intrinsic(@llvm.amdgcn.readlane), [[COPY2]](s32), [[COPY1]](s32)
+    %0:_(s32) = COPY $sgpr0
+    %1:_(s32) = COPY $sgpr1
+    %2:_(s32) = G_INTRINSIC intrinsic(@llvm.amdgcn.readlane), %0, %1
+...
+
+---
+name: readlane_vs
+legalized: true
+
+body: |
+  bb.0:
+    liveins: $vgpr0, $sgpr0
+    ; CHECK-LABEL: name: readlane_vs
+    ; CHECK: [[COPY:%[0-9]+]]:vgpr(s32) = COPY $vgpr0
+    ; CHECK: [[COPY1:%[0-9]+]]:sgpr(s32) = COPY $sgpr0
+    ; CHECK: [[INT:%[0-9]+]]:sgpr(s32) = G_INTRINSIC intrinsic(@llvm.amdgcn.readlane), [[COPY]](s32), [[COPY1]](s32)
+    %0:_(s32) = COPY $vgpr0
+    %1:_(s32) = COPY $sgpr0
+    %2:_(s32) = G_INTRINSIC intrinsic(@llvm.amdgcn.readlane), %0, %1
+...
+
+---
+name: readlane_vv
+legalized: true
+
+body: |
+  bb.0:
+    liveins: $vgpr0, $vgpr1
+    ; CHECK-LABEL: name: readlane_vv
+    ; CHECK: [[COPY:%[0-9]+]]:vgpr(s32) = COPY $vgpr0
+    ; CHECK: [[COPY1:%[0-9]+]]:vgpr_32(s32) = COPY $vgpr1
+    ; CHECK: [[V_READFIRSTLANE_B32_:%[0-9]+]]:sreg_32_xm0 = V_READFIRSTLANE_B32 [[COPY1]](s32), implicit $exec
+    ; CHECK: [[INT:%[0-9]+]]:sgpr(s32) = G_INTRINSIC intrinsic(@llvm.amdgcn.readlane), [[COPY]](s32), [[V_READFIRSTLANE_B32_]]
+    %0:_(s32) = COPY $vgpr0
+    %1:_(s32) = COPY $vgpr1
+    %2:_(s32) = G_INTRINSIC intrinsic(@llvm.amdgcn.readlane), %0, %1
+...
+
+---
+name: readlane_sv
+legalized: true
+
+body: |
+  bb.0:
+    liveins: $vgpr0, $sgpr0
+    ; CHECK-LABEL: name: readlane_sv
+    ; CHECK: [[COPY:%[0-9]+]]:sgpr(s32) = COPY $sgpr0
+    ; CHECK: [[COPY1:%[0-9]+]]:vgpr_32(s32) = COPY $vgpr0
+    ; CHECK: [[COPY2:%[0-9]+]]:vgpr(s32) = COPY [[COPY]](s32)
+    ; CHECK: [[V_READFIRSTLANE_B32_:%[0-9]+]]:sreg_32_xm0 = V_READFIRSTLANE_B32 [[COPY1]](s32), implicit $exec
+    ; CHECK: [[INT:%[0-9]+]]:sgpr(s32) = G_INTRINSIC intrinsic(@llvm.amdgcn.readlane), [[COPY2]](s32), [[V_READFIRSTLANE_B32_]]
+    %0:_(s32) = COPY $sgpr0
+    %1:_(s32) = COPY $vgpr0
+    %2:_(s32) = G_INTRINSIC intrinsic(@llvm.amdgcn.readlane), %0, %1
+...