diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index 8a26703..2fdd2ff 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -657,35 +657,14 @@
     MI.eraseFromParent();
     return Legalized;
   }
-  case TargetOpcode::G_SEXT: {
-    if (TypeIdx != 0)
-      return UnableToLegalize;
-
-    Register SrcReg = MI.getOperand(1).getReg();
-    LLT SrcTy = MRI.getType(SrcReg);
-
-    // FIXME: support the general case where the requested NarrowTy may not be
-    // the same as the source type. E.g. s128 = sext(s32)
-    if ((SrcTy.getSizeInBits() != SizeOp0 / 2) ||
-        SrcTy.getSizeInBits() != NarrowTy.getSizeInBits()) {
-      LLVM_DEBUG(dbgs() << "Can't narrow sext to type " << NarrowTy << "\n");
-      return UnableToLegalize;
-    }
-
-    // Shift the sign bit of the low register through the high register.
-    auto ShiftAmt =
-        MIRBuilder.buildConstant(LLT::scalar(64), NarrowTy.getSizeInBits() - 1);
-    auto Shift = MIRBuilder.buildAShr(NarrowTy, SrcReg, ShiftAmt);
-    MIRBuilder.buildMerge(MI.getOperand(0).getReg(), {SrcReg, Shift.getReg(0)});
-    MI.eraseFromParent();
-    return Legalized;
-  }
+  case TargetOpcode::G_SEXT:
   case TargetOpcode::G_ZEXT:
   case TargetOpcode::G_ANYEXT: {
     if (TypeIdx != 0)
       return UnableToLegalize;
 
-    LLT SrcTy = MRI.getType(MI.getOperand(1).getReg());
+    Register SrcReg = MI.getOperand(1).getReg();
+    LLT SrcTy = MRI.getType(SrcReg);
     uint64_t SizeOp1 = SrcTy.getSizeInBits();
     if (SizeOp0 % SizeOp1 != 0)
       return UnableToLegalize;
@@ -693,13 +672,19 @@
     Register PadReg;
     if (MI.getOpcode() == TargetOpcode::G_ZEXT)
       PadReg = MIRBuilder.buildConstant(SrcTy, 0).getReg(0);
-    else
+    else if (MI.getOpcode() == TargetOpcode::G_ANYEXT)
       PadReg = MIRBuilder.buildUndef(SrcTy).getReg(0);
+    else {
+      // Shift the sign bit of the low register through the high register.
+      auto ShiftAmt =
+        MIRBuilder.buildConstant(LLT::scalar(64), SrcTy.getSizeInBits() - 1);
+      PadReg = MIRBuilder.buildAShr(SrcTy, SrcReg, ShiftAmt).getReg(0);
+    }
 
     // Generate a merge where the bottom bits are taken from the source, and
-    // zero/impdef everything else.
+    // zero/impdef/sign bit everything else.
     unsigned NumParts = SizeOp0 / SizeOp1;
-    SmallVector<Register, 4> Srcs = {MI.getOperand(1).getReg()};
+    SmallVector<Register, 4> Srcs = {SrcReg};
     for (unsigned Part = 1; Part < NumParts; ++Part)
       Srcs.push_back(PadReg);
     MIRBuilder.buildMerge(MI.getOperand(0).getReg(), Srcs);
diff --git a/llvm/test/CodeGen/AMDGPU/GlobalISel/legalize-sext.mir b/llvm/test/CodeGen/AMDGPU/GlobalISel/legalize-sext.mir
index cbff2b8..1febfef 100644
--- a/llvm/test/CodeGen/AMDGPU/GlobalISel/legalize-sext.mir
+++ b/llvm/test/CodeGen/AMDGPU/GlobalISel/legalize-sext.mir
@@ -1,5 +1,5 @@
 # NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
-# RUN: llc -O0 -mtriple=amdgcn-mesa-mesa3d -mcpu=fiji -run-pass=legalizer -global-isel-abort=0 %s -o - | FileCheck %s
+# RUN: llc -O0 -mtriple=amdgcn-mesa-mesa3d -mcpu=fiji -run-pass=legalizer %s -o - | FileCheck %s
 
 ---
 name: test_sext_s32_to_s64
@@ -336,8 +336,10 @@
 
     ; CHECK-LABEL: name: test_sext_s32_to_s128
     ; CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY $vgpr0
-    ; CHECK: [[SEXT:%[0-9]+]]:_(s128) = G_SEXT [[COPY]](s32)
-    ; CHECK: S_ENDPGM 0, implicit [[SEXT]](s128)
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 31
+    ; CHECK: [[ASHR:%[0-9]+]]:_(s32) = G_ASHR [[COPY]], [[C]](s32)
+    ; CHECK: [[MV:%[0-9]+]]:_(s128) = G_MERGE_VALUES [[COPY]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32)
+    ; CHECK: S_ENDPGM 0, implicit [[MV]](s128)
     %0:_(s32) = COPY $vgpr0
     %1:_(s128) = G_SEXT %0
     S_ENDPGM 0, implicit %1
@@ -351,8 +353,10 @@
 
     ; CHECK-LABEL: name: test_sext_s32_to_s256
     ; CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY $vgpr0
-    ; CHECK: [[SEXT:%[0-9]+]]:_(s256) = G_SEXT [[COPY]](s32)
-    ; CHECK: S_ENDPGM 0, implicit [[SEXT]](s256)
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 31
+    ; CHECK: [[ASHR:%[0-9]+]]:_(s32) = G_ASHR [[COPY]], [[C]](s32)
+    ; CHECK: [[MV:%[0-9]+]]:_(s256) = G_MERGE_VALUES [[COPY]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32)
+    ; CHECK: S_ENDPGM 0, implicit [[MV]](s256)
     %0:_(s32) = COPY $vgpr0
     %1:_(s256) = G_SEXT %0
     S_ENDPGM 0, implicit %1
@@ -366,8 +370,10 @@
 
     ; CHECK-LABEL: name: test_sext_s32_to_s512
     ; CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY $vgpr0
-    ; CHECK: [[SEXT:%[0-9]+]]:_(s512) = G_SEXT [[COPY]](s32)
-    ; CHECK: S_ENDPGM 0, implicit [[SEXT]](s512)
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 31
+    ; CHECK: [[ASHR:%[0-9]+]]:_(s32) = G_ASHR [[COPY]], [[C]](s32)
+    ; CHECK: [[MV:%[0-9]+]]:_(s512) = G_MERGE_VALUES [[COPY]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32)
+    ; CHECK: S_ENDPGM 0, implicit [[MV]](s512)
     %0:_(s32) = COPY $vgpr0
     %1:_(s512) = G_SEXT %0
     S_ENDPGM 0, implicit %1
@@ -381,8 +387,10 @@
 
     ; CHECK-LABEL: name: test_sext_s32_to_s1024
     ; CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY $vgpr0
-    ; CHECK: [[SEXT:%[0-9]+]]:_(s1024) = G_SEXT [[COPY]](s32)
-    ; CHECK: S_ENDPGM 0, implicit [[SEXT]](s1024)
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 31
+    ; CHECK: [[ASHR:%[0-9]+]]:_(s32) = G_ASHR [[COPY]], [[C]](s32)
+    ; CHECK: [[MV:%[0-9]+]]:_(s1024) = G_MERGE_VALUES [[COPY]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32), [[ASHR]](s32)
+    ; CHECK: S_ENDPGM 0, implicit [[MV]](s1024)
     %0:_(s32) = COPY $vgpr0
     %1:_(s1024) = G_SEXT %0
     S_ENDPGM 0, implicit %1
@@ -413,8 +421,10 @@
 
     ; CHECK-LABEL: name: test_sext_s64_to_s256
     ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $vgpr0_vgpr1
-    ; CHECK: [[SEXT:%[0-9]+]]:_(s256) = G_SEXT [[COPY]](s64)
-    ; CHECK: S_ENDPGM 0, implicit [[SEXT]](s256)
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 63
+    ; CHECK: [[ASHR:%[0-9]+]]:_(s64) = G_ASHR [[COPY]], [[C]](s32)
+    ; CHECK: [[MV:%[0-9]+]]:_(s256) = G_MERGE_VALUES [[COPY]](s64), [[ASHR]](s64), [[ASHR]](s64), [[ASHR]](s64)
+    ; CHECK: S_ENDPGM 0, implicit [[MV]](s256)
     %0:_(s64) = COPY $vgpr0_vgpr1
     %1:_(s256) = G_SEXT %0
     S_ENDPGM 0, implicit %1
@@ -428,8 +438,10 @@
 
     ; CHECK-LABEL: name: test_sext_s64_to_s512
     ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $vgpr0_vgpr1
-    ; CHECK: [[SEXT:%[0-9]+]]:_(s512) = G_SEXT [[COPY]](s64)
-    ; CHECK: S_ENDPGM 0, implicit [[SEXT]](s512)
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 63
+    ; CHECK: [[ASHR:%[0-9]+]]:_(s64) = G_ASHR [[COPY]], [[C]](s32)
+    ; CHECK: [[MV:%[0-9]+]]:_(s512) = G_MERGE_VALUES [[COPY]](s64), [[ASHR]](s64), [[ASHR]](s64), [[ASHR]](s64), [[ASHR]](s64), [[ASHR]](s64), [[ASHR]](s64), [[ASHR]](s64)
+    ; CHECK: S_ENDPGM 0, implicit [[MV]](s512)
     %0:_(s64) = COPY $vgpr0_vgpr1
     %1:_(s512) = G_SEXT %0
     S_ENDPGM 0, implicit %1
@@ -443,8 +455,10 @@
 
     ; CHECK-LABEL: name: test_sext_s64_to_s1024
     ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $vgpr0_vgpr1
-    ; CHECK: [[SEXT:%[0-9]+]]:_(s1024) = G_SEXT [[COPY]](s64)
-    ; CHECK: S_ENDPGM 0, implicit [[SEXT]](s1024)
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 63
+    ; CHECK: [[ASHR:%[0-9]+]]:_(s64) = G_ASHR [[COPY]], [[C]](s32)
+    ; CHECK: [[MV:%[0-9]+]]:_(s1024) = G_MERGE_VALUES [[COPY]](s64), [[ASHR]](s64), [[ASHR]](s64), [[ASHR]](s64), [[ASHR]](s64), [[ASHR]](s64), [[ASHR]](s64), [[ASHR]](s64), [[ASHR]](s64), [[ASHR]](s64), [[ASHR]](s64), [[ASHR]](s64), [[ASHR]](s64), [[ASHR]](s64), [[ASHR]](s64), [[ASHR]](s64)
+    ; CHECK: S_ENDPGM 0, implicit [[MV]](s1024)
     %0:_(s64) = COPY $vgpr0_vgpr1
     %1:_(s1024) = G_SEXT %0
     S_ENDPGM 0, implicit %1
@@ -469,8 +483,27 @@
 
     ; CHECK-LABEL: name: test_sext_s128_to_s256
     ; CHECK: [[COPY:%[0-9]+]]:_(s128) = COPY $vgpr0_vgpr1_vgpr2_vgpr3
-    ; CHECK: [[SEXT:%[0-9]+]]:_(s256) = G_SEXT [[COPY]](s128)
-    ; CHECK: S_ENDPGM 0, implicit [[SEXT]](s256)
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 127
+    ; CHECK: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 64
+    ; CHECK: [[UV:%[0-9]+]]:_(s64), [[UV1:%[0-9]+]]:_(s64) = G_UNMERGE_VALUES [[COPY]](s128)
+    ; CHECK: [[SUB:%[0-9]+]]:_(s32) = G_SUB [[C]], [[C1]]
+    ; CHECK: [[SUB1:%[0-9]+]]:_(s32) = G_SUB [[C1]], [[C]]
+    ; CHECK: [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+    ; CHECK: [[ICMP:%[0-9]+]]:_(s1) = G_ICMP intpred(ult), [[C]](s32), [[C1]]
+    ; CHECK: [[ICMP1:%[0-9]+]]:_(s1) = G_ICMP intpred(eq), [[C]](s32), [[C2]]
+    ; CHECK: [[ASHR:%[0-9]+]]:_(s64) = G_ASHR [[UV1]], [[C]](s32)
+    ; CHECK: [[LSHR:%[0-9]+]]:_(s64) = G_LSHR [[UV]], [[C]](s32)
+    ; CHECK: [[SHL:%[0-9]+]]:_(s64) = G_SHL [[UV1]], [[SUB1]](s32)
+    ; CHECK: [[OR:%[0-9]+]]:_(s64) = G_OR [[LSHR]], [[SHL]]
+    ; CHECK: [[C3:%[0-9]+]]:_(s32) = G_CONSTANT i32 63
+    ; CHECK: [[ASHR1:%[0-9]+]]:_(s64) = G_ASHR [[UV1]], [[C3]](s32)
+    ; CHECK: [[ASHR2:%[0-9]+]]:_(s64) = G_ASHR [[UV1]], [[SUB]](s32)
+    ; CHECK: [[SELECT:%[0-9]+]]:_(s64) = G_SELECT [[ICMP]](s1), [[OR]], [[ASHR2]]
+    ; CHECK: [[SELECT1:%[0-9]+]]:_(s64) = G_SELECT [[ICMP1]](s1), [[UV]], [[SELECT]]
+    ; CHECK: [[SELECT2:%[0-9]+]]:_(s64) = G_SELECT [[ICMP]](s1), [[ASHR]], [[ASHR1]]
+    ; CHECK: [[MV:%[0-9]+]]:_(s128) = G_MERGE_VALUES [[SELECT1]](s64), [[SELECT2]](s64)
+    ; CHECK: [[MV1:%[0-9]+]]:_(s256) = G_MERGE_VALUES [[COPY]](s128), [[MV]](s128)
+    ; CHECK: S_ENDPGM 0, implicit [[MV1]](s256)
     %0:_(s128) = COPY $vgpr0_vgpr1_vgpr2_vgpr3
     %1:_(s256) = G_SEXT %0
     S_ENDPGM 0, implicit %1