Index: llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp
===================================================================
--- llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp
+++ llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp
@@ -1497,7 +1497,8 @@
 }
 
 bool AMDGPUInstructionSelector::selectG_SZA_EXT(MachineInstr &I) const {
-  bool Signed = I.getOpcode() == AMDGPU::G_SEXT;
+  bool InReg = I.getOpcode() == AMDGPU::G_SEXT_INREG;
+  bool Signed = I.getOpcode() == AMDGPU::G_SEXT || InReg;
   const DebugLoc &DL = I.getDebugLoc();
   MachineBasicBlock &MBB = *I.getParent();
   const Register DstReg = I.getOperand(0).getReg();
@@ -1505,7 +1506,8 @@
 
   const LLT DstTy = MRI->getType(DstReg);
   const LLT SrcTy = MRI->getType(SrcReg);
-  const unsigned SrcSize = SrcTy.getSizeInBits();
+  const unsigned SrcSize = I.getOpcode() == AMDGPU::G_SEXT_INREG ?
+    I.getOperand(2).getImm() : SrcTy.getSizeInBits();
   const unsigned DstSize = DstTy.getSizeInBits();
   if (!DstTy.isScalar())
     return false;
@@ -1541,7 +1543,9 @@
   }
 
   if (SrcBank->getID() == AMDGPU::SGPRRegBankID && DstSize <= 64) {
-    if (!RBI.constrainGenericRegister(SrcReg, AMDGPU::SReg_32RegClass, *MRI))
+    const TargetRegisterClass &SrcRC = InReg && DstSize > 32 ?
+      AMDGPU::SReg_64RegClass : AMDGPU::SReg_32RegClass;
+    if (!RBI.constrainGenericRegister(SrcReg, SrcRC, *MRI))
       return false;
 
     if (Signed && DstSize == 32 && (SrcSize == 8 || SrcSize == 16)) {
@@ -1557,13 +1561,15 @@
     const unsigned BFE32 = Signed ? AMDGPU::S_BFE_I32 : AMDGPU::S_BFE_U32;
 
     // Scalar BFE is encoded as S1[5:0] = offset, S1[22:16]= width.
-    if (DstSize > 32 && SrcSize <= 32) {
+    if (DstSize > 32 && (SrcSize <= 32 || InReg)) {
       // We need a 64-bit register source, but the high bits don't matter.
       Register ExtReg = MRI->createVirtualRegister(&AMDGPU::SReg_64RegClass);
       Register UndefReg = MRI->createVirtualRegister(&AMDGPU::SReg_32RegClass);
+      unsigned SubReg = InReg ? AMDGPU::sub0 : 0;
+
       BuildMI(MBB, I, DL, TII.get(AMDGPU::IMPLICIT_DEF), UndefReg);
       BuildMI(MBB, I, DL, TII.get(AMDGPU::REG_SEQUENCE), ExtReg)
-        .addReg(SrcReg)
+        .addReg(SrcReg, 0, SubReg)
         .addImm(AMDGPU::sub0)
         .addReg(UndefReg)
         .addImm(AMDGPU::sub1);
@@ -2122,6 +2128,7 @@
   case TargetOpcode::G_SEXT:
   case TargetOpcode::G_ZEXT:
   case TargetOpcode::G_ANYEXT:
+  case TargetOpcode::G_SEXT_INREG:
     if (selectImpl(I, *CoverageInfo))
       return true;
     return selectG_SZA_EXT(I);
Index: llvm/test/CodeGen/AMDGPU/GlobalISel/inst-select-sext-inreg.mir
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/AMDGPU/GlobalISel/inst-select-sext-inreg.mir
@@ -0,0 +1,323 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -march=amdgcn -mcpu=tahiti -run-pass=instruction-select -verify-machineinstrs -global-isel %s -o - | FileCheck -check-prefix=GCN %s
+
+---
+
+name: sext_inreg_sgpr_s32_1
+legalized:       true
+regBankSelected: true
+body: |
+  bb.0:
+    liveins: $sgpr0
+
+    ; GCN-LABEL: name: sext_inreg_sgpr_s32_1
+    ; GCN: [[COPY:%[0-9]+]]:sreg_32 = COPY $sgpr0
+    ; GCN: [[S_BFE_I32_:%[0-9]+]]:sreg_32 = S_BFE_I32 [[COPY]], 65536, implicit-def $scc
+    ; GCN: $sgpr0 = COPY [[S_BFE_I32_]]
+    %0:sgpr(s32) = COPY $sgpr0
+    %1:sgpr(s32) = G_SEXT_INREG %0, 1
+    $sgpr0 = COPY %1
+...
+
+---
+
+name: sext_inreg_sgpr_s32_2
+legalized:       true
+regBankSelected: true
+body: |
+  bb.0:
+    liveins: $sgpr0
+
+    ; GCN-LABEL: name: sext_inreg_sgpr_s32_2
+    ; GCN: [[COPY:%[0-9]+]]:sreg_32 = COPY $sgpr0
+    ; GCN: [[S_BFE_I32_:%[0-9]+]]:sreg_32 = S_BFE_I32 [[COPY]], 131072, implicit-def $scc
+    ; GCN: $sgpr0 = COPY [[S_BFE_I32_]]
+    %0:sgpr(s32) = COPY $sgpr0
+    %1:sgpr(s32) = G_SEXT_INREG %0, 2
+    $sgpr0 = COPY %1
+...
+
+---
+
+name: sext_inreg_sgpr_s32_8
+legalized:       true
+regBankSelected: true
+body: |
+  bb.0:
+    liveins: $sgpr0
+
+    ; GCN-LABEL: name: sext_inreg_sgpr_s32_8
+    ; GCN: [[COPY:%[0-9]+]]:sreg_32 = COPY $sgpr0
+    ; GCN: [[S_SEXT_I32_I8_:%[0-9]+]]:sreg_32 = S_SEXT_I32_I8 [[COPY]]
+    ; GCN: $sgpr0 = COPY [[S_SEXT_I32_I8_]]
+    %0:sgpr(s32) = COPY $sgpr0
+    %1:sgpr(s32) = G_SEXT_INREG %0, 8
+    $sgpr0 = COPY %1
+...
+
+---
+
+name: sext_inreg_sgpr_s32_16
+legalized:       true
+regBankSelected: true
+body: |
+  bb.0:
+    liveins: $sgpr0
+
+    ; GCN-LABEL: name: sext_inreg_sgpr_s32_16
+    ; GCN: [[COPY:%[0-9]+]]:sreg_32 = COPY $sgpr0
+    ; GCN: [[S_SEXT_I32_I16_:%[0-9]+]]:sreg_32 = S_SEXT_I32_I16 [[COPY]]
+    ; GCN: $sgpr0 = COPY [[S_SEXT_I32_I16_]]
+    %0:sgpr(s32) = COPY $sgpr0
+    %1:sgpr(s32) = G_SEXT_INREG %0, 16
+    $sgpr0 = COPY %1
+...
+
+---
+
+name: sext_inreg_sgpr_s32_31
+legalized:       true
+regBankSelected: true
+body: |
+  bb.0:
+    liveins: $sgpr0
+
+    ; GCN-LABEL: name: sext_inreg_sgpr_s32_31
+    ; GCN: [[COPY:%[0-9]+]]:sreg_32 = COPY $sgpr0
+    ; GCN: [[S_BFE_I32_:%[0-9]+]]:sreg_32 = S_BFE_I32 [[COPY]], 2031616, implicit-def $scc
+    ; GCN: $sgpr0 = COPY [[S_BFE_I32_]]
+    %0:sgpr(s32) = COPY $sgpr0
+    %1:sgpr(s32) = G_SEXT_INREG %0, 31
+    $sgpr0 = COPY %1
+...
+
+---
+
+name: sext_inreg_sgpr_s64_1
+legalized:       true
+regBankSelected: true
+body: |
+  bb.0:
+    liveins: $sgpr0_sgpr1
+
+    ; GCN-LABEL: name: sext_inreg_sgpr_s64_1
+    ; GCN: [[COPY:%[0-9]+]]:sreg_64 = COPY $sgpr0_sgpr1
+    ; GCN: [[DEF:%[0-9]+]]:sreg_32 = IMPLICIT_DEF
+    ; GCN: [[REG_SEQUENCE:%[0-9]+]]:sreg_64 = REG_SEQUENCE [[COPY]].sub0, %subreg.sub0, [[DEF]], %subreg.sub1
+    ; GCN: [[S_BFE_I64_:%[0-9]+]]:sreg_64 = S_BFE_I64 [[REG_SEQUENCE]], 65536, implicit-def $scc
+    ; GCN: $sgpr0_sgpr1 = COPY [[S_BFE_I64_]]
+    %0:sgpr(s64) = COPY $sgpr0_sgpr1
+    %1:sgpr(s64) = G_SEXT_INREG %0, 1
+    $sgpr0_sgpr1 = COPY %1
+...
+
+---
+
+name: sext_inreg_sgpr_s64_2
+legalized:       true
+regBankSelected: true
+body: |
+  bb.0:
+    liveins: $sgpr0_sgpr1
+
+    ; GCN-LABEL: name: sext_inreg_sgpr_s64_2
+    ; GCN: [[COPY:%[0-9]+]]:sreg_64 = COPY $sgpr0_sgpr1
+    ; GCN: [[DEF:%[0-9]+]]:sreg_32 = IMPLICIT_DEF
+    ; GCN: [[REG_SEQUENCE:%[0-9]+]]:sreg_64 = REG_SEQUENCE [[COPY]].sub0, %subreg.sub0, [[DEF]], %subreg.sub1
+    ; GCN: [[S_BFE_I64_:%[0-9]+]]:sreg_64 = S_BFE_I64 [[REG_SEQUENCE]], 131072, implicit-def $scc
+    ; GCN: $sgpr0_sgpr1 = COPY [[S_BFE_I64_]]
+    %0:sgpr(s64) = COPY $sgpr0_sgpr1
+    %1:sgpr(s64) = G_SEXT_INREG %0, 2
+    $sgpr0_sgpr1 = COPY %1
+...
+
+---
+
+name: sext_inreg_sgpr_s64_8
+legalized:       true
+regBankSelected: true
+body: |
+  bb.0:
+    liveins: $sgpr0_sgpr1
+
+    ; GCN-LABEL: name: sext_inreg_sgpr_s64_8
+    ; GCN: [[COPY:%[0-9]+]]:sreg_64 = COPY $sgpr0_sgpr1
+    ; GCN: [[DEF:%[0-9]+]]:sreg_32 = IMPLICIT_DEF
+    ; GCN: [[REG_SEQUENCE:%[0-9]+]]:sreg_64 = REG_SEQUENCE [[COPY]].sub0, %subreg.sub0, [[DEF]], %subreg.sub1
+    ; GCN: [[S_BFE_I64_:%[0-9]+]]:sreg_64 = S_BFE_I64 [[REG_SEQUENCE]], 524288, implicit-def $scc
+    ; GCN: $sgpr0_sgpr1 = COPY [[S_BFE_I64_]]
+    %0:sgpr(s64) = COPY $sgpr0_sgpr1
+    %1:sgpr(s64) = G_SEXT_INREG %0, 8
+    $sgpr0_sgpr1 = COPY %1
+...
+
+---
+
+name: sext_inreg_sgpr_s64_16
+legalized:       true
+regBankSelected: true
+body: |
+  bb.0:
+    liveins: $sgpr0_sgpr1
+
+    ; GCN-LABEL: name: sext_inreg_sgpr_s64_16
+    ; GCN: [[COPY:%[0-9]+]]:sreg_64 = COPY $sgpr0_sgpr1
+    ; GCN: [[DEF:%[0-9]+]]:sreg_32 = IMPLICIT_DEF
+    ; GCN: [[REG_SEQUENCE:%[0-9]+]]:sreg_64 = REG_SEQUENCE [[COPY]].sub0, %subreg.sub0, [[DEF]], %subreg.sub1
+    ; GCN: [[S_BFE_I64_:%[0-9]+]]:sreg_64 = S_BFE_I64 [[REG_SEQUENCE]], 1048576, implicit-def $scc
+    ; GCN: $sgpr0_sgpr1 = COPY [[S_BFE_I64_]]
+    %0:sgpr(s64) = COPY $sgpr0_sgpr1
+    %1:sgpr(s64) = G_SEXT_INREG %0, 16
+    $sgpr0_sgpr1 = COPY %1
+...
+
+---
+
+name: sext_inreg_sgpr_s64_31
+legalized:       true
+regBankSelected: true
+body: |
+  bb.0:
+    liveins: $sgpr0_sgpr1
+
+    ; GCN-LABEL: name: sext_inreg_sgpr_s64_31
+    ; GCN: [[COPY:%[0-9]+]]:sreg_64 = COPY $sgpr0_sgpr1
+    ; GCN: [[DEF:%[0-9]+]]:sreg_32 = IMPLICIT_DEF
+    ; GCN: [[REG_SEQUENCE:%[0-9]+]]:sreg_64 = REG_SEQUENCE [[COPY]].sub0, %subreg.sub0, [[DEF]], %subreg.sub1
+    ; GCN: [[S_BFE_I64_:%[0-9]+]]:sreg_64 = S_BFE_I64 [[REG_SEQUENCE]], 2031616, implicit-def $scc
+    ; GCN: $sgpr0_sgpr1 = COPY [[S_BFE_I64_]]
+    %0:sgpr(s64) = COPY $sgpr0_sgpr1
+    %1:sgpr(s64) = G_SEXT_INREG %0, 31
+    $sgpr0_sgpr1 = COPY %1
+...
+
+# Ideally this degenerate case would have been replaceed with a 32-bit shift by combines.
+---
+
+name: sext_inreg_sgpr_s64_32
+legalized:       true
+regBankSelected: true
+body: |
+  bb.0:
+    liveins: $sgpr0_sgpr1
+
+    ; GCN-LABEL: name: sext_inreg_sgpr_s64_32
+    ; GCN: [[COPY:%[0-9]+]]:sreg_64 = COPY $sgpr0_sgpr1
+    ; GCN: [[DEF:%[0-9]+]]:sreg_32 = IMPLICIT_DEF
+    ; GCN: [[REG_SEQUENCE:%[0-9]+]]:sreg_64 = REG_SEQUENCE [[COPY]].sub0, %subreg.sub0, [[DEF]], %subreg.sub1
+    ; GCN: [[S_BFE_I64_:%[0-9]+]]:sreg_64 = S_BFE_I64 [[REG_SEQUENCE]], 2097152, implicit-def $scc
+    ; GCN: $sgpr0_sgpr1 = COPY [[S_BFE_I64_]]
+    %0:sgpr(s64) = COPY $sgpr0_sgpr1
+    %1:sgpr(s64) = G_SEXT_INREG %0, 32
+    $sgpr0_sgpr1 = COPY %1
+...
+
+---
+
+name: sext_inreg_sgpr_s64_63
+legalized:       true
+regBankSelected: true
+body: |
+  bb.0:
+    liveins: $sgpr0_sgpr1
+
+    ; GCN-LABEL: name: sext_inreg_sgpr_s64_63
+    ; GCN: [[COPY:%[0-9]+]]:sreg_64 = COPY $sgpr0_sgpr1
+    ; GCN: [[DEF:%[0-9]+]]:sreg_32 = IMPLICIT_DEF
+    ; GCN: [[REG_SEQUENCE:%[0-9]+]]:sreg_64 = REG_SEQUENCE [[COPY]].sub0, %subreg.sub0, [[DEF]], %subreg.sub1
+    ; GCN: [[S_BFE_I64_:%[0-9]+]]:sreg_64 = S_BFE_I64 [[REG_SEQUENCE]], 4128768, implicit-def $scc
+    ; GCN: $sgpr0_sgpr1 = COPY [[S_BFE_I64_]]
+    %0:sgpr(s64) = COPY $sgpr0_sgpr1
+    %1:sgpr(s64) = G_SEXT_INREG %0, 63
+    $sgpr0_sgpr1 = COPY %1
+...
+
+---
+
+name: sext_inreg_vgpr_s32_1
+legalized:       true
+regBankSelected: true
+body: |
+  bb.0:
+    liveins: $vgpr0
+
+    ; GCN-LABEL: name: sext_inreg_vgpr_s32_1
+    ; GCN: [[COPY:%[0-9]+]]:vgpr_32 = COPY $vgpr0
+    ; GCN: [[V_BFE_I32_:%[0-9]+]]:vgpr_32 = V_BFE_I32 [[COPY]], 0, 1, implicit $exec
+    ; GCN: $vgpr0 = COPY [[V_BFE_I32_]]
+    %0:vgpr(s32) = COPY $vgpr0
+    %1:vgpr(s32) = G_SEXT_INREG %0, 1
+    $vgpr0 = COPY %1
+...
+
+---
+
+name: sext_inreg_vgpr_s32_2
+legalized:       true
+regBankSelected: true
+body: |
+  bb.0:
+    liveins: $vgpr0
+
+    ; GCN-LABEL: name: sext_inreg_vgpr_s32_2
+    ; GCN: [[COPY:%[0-9]+]]:vgpr_32 = COPY $vgpr0
+    ; GCN: [[V_BFE_I32_:%[0-9]+]]:vgpr_32 = V_BFE_I32 [[COPY]], 0, 2, implicit $exec
+    ; GCN: $vgpr0 = COPY [[V_BFE_I32_]]
+    %0:vgpr(s32) = COPY $vgpr0
+    %1:vgpr(s32) = G_SEXT_INREG %0, 2
+    $vgpr0 = COPY %1
+...
+
+---
+
+name: sext_inreg_vgpr_s32_8
+legalized:       true
+regBankSelected: true
+body: |
+  bb.0:
+    liveins: $vgpr0
+
+    ; GCN-LABEL: name: sext_inreg_vgpr_s32_8
+    ; GCN: [[COPY:%[0-9]+]]:vgpr_32 = COPY $vgpr0
+    ; GCN: [[V_BFE_I32_:%[0-9]+]]:vgpr_32 = V_BFE_I32 [[COPY]], 0, 8, implicit $exec
+    ; GCN: $vgpr0 = COPY [[V_BFE_I32_]]
+    %0:vgpr(s32) = COPY $vgpr0
+    %1:vgpr(s32) = G_SEXT_INREG %0, 8
+    $vgpr0 = COPY %1
+...
+
+---
+
+name: sext_inreg_vgpr_s32_16
+legalized:       true
+regBankSelected: true
+body: |
+  bb.0:
+    liveins: $vgpr0
+
+    ; GCN-LABEL: name: sext_inreg_vgpr_s32_16
+    ; GCN: [[COPY:%[0-9]+]]:vgpr_32 = COPY $vgpr0
+    ; GCN: [[V_BFE_I32_:%[0-9]+]]:vgpr_32 = V_BFE_I32 [[COPY]], 0, 16, implicit $exec
+    ; GCN: $vgpr0 = COPY [[V_BFE_I32_]]
+    %0:vgpr(s32) = COPY $vgpr0
+    %1:vgpr(s32) = G_SEXT_INREG %0, 16
+    $vgpr0 = COPY %1
+...
+
+---
+
+name: sext_inreg_vgpr_s32_31
+legalized:       true
+regBankSelected: true
+body: |
+  bb.0:
+    liveins: $vgpr0
+
+    ; GCN-LABEL: name: sext_inreg_vgpr_s32_31
+    ; GCN: [[COPY:%[0-9]+]]:vgpr_32 = COPY $vgpr0
+    ; GCN: [[V_BFE_I32_:%[0-9]+]]:vgpr_32 = V_BFE_I32 [[COPY]], 0, 31, implicit $exec
+    ; GCN: $vgpr0 = COPY [[V_BFE_I32_]]
+    %0:vgpr(s32) = COPY $vgpr0
+    %1:vgpr(s32) = G_SEXT_INREG %0, 31
+    $vgpr0 = COPY %1
+...