Index: include/llvm/CodeGen/GlobalISel/LegalizerHelper.h
===================================================================
--- include/llvm/CodeGen/GlobalISel/LegalizerHelper.h
+++ include/llvm/CodeGen/GlobalISel/LegalizerHelper.h
@@ -235,6 +235,7 @@
   LegalizeResult lowerShuffleVector(MachineInstr &MI);
   LegalizeResult lowerDynStackAlloc(MachineInstr &MI);
   LegalizeResult lowerExtract(MachineInstr &MI);
+  LegalizeResult lowerInsert(MachineInstr &MI);
 
 private:
   MachineRegisterInfo &MRI;
Index: lib/CodeGen/GlobalISel/LegalizerHelper.cpp
===================================================================
--- lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -2272,6 +2272,8 @@
     return lowerDynStackAlloc(MI);
   case G_EXTRACT:
     return lowerExtract(MI);
+  case G_INSERT:
+    return lowerInsert(MI);
   }
 }
 
@@ -4218,3 +4220,42 @@
 
   return UnableToLegalize;
 }
+
+LegalizerHelper::LegalizeResult LegalizerHelper::lowerInsert(MachineInstr &MI) {
+  Register Dst = MI.getOperand(0).getReg();
+  Register Src = MI.getOperand(1).getReg();
+  Register InsertSrc = MI.getOperand(2).getReg();
+  uint64_t Offset = MI.getOperand(3).getImm();
+
+  LLT DstTy = MRI.getType(Src);
+  LLT InsertTy = MRI.getType(InsertSrc);
+
+  if (InsertTy.isScalar() &&
+      (DstTy.isScalar() ||
+       (DstTy.isVector() && DstTy.getElementType() == InsertTy))) {
+    LLT IntDstTy = DstTy;
+    if (!DstTy.isScalar()) {
+      IntDstTy = LLT::scalar(DstTy.getSizeInBits());
+      Src = MIRBuilder.buildBitcast(IntDstTy, Src).getReg(0);
+    }
+
+    Register ExtInsSrc = MIRBuilder.buildZExt(IntDstTy, InsertSrc).getReg(0);
+    if (Offset != 0) {
+      auto ShiftAmt = MIRBuilder.buildConstant(IntDstTy, Offset);
+      ExtInsSrc = MIRBuilder.buildShl(IntDstTy, ExtInsSrc, ShiftAmt).getReg(0);
+    }
+
+    APInt MaskVal = ~APInt::getBitsSet(DstTy.getSizeInBits(), Offset,
+                                       InsertTy.getSizeInBits());
+
+    auto Mask = MIRBuilder.buildConstant(IntDstTy, MaskVal);
+    auto MaskedSrc = MIRBuilder.buildAnd(IntDstTy, Src, Mask);
+    auto Or = MIRBuilder.buildOr(IntDstTy, MaskedSrc, ExtInsSrc);
+
+    MIRBuilder.buildBitcast(Dst, Or);
+    MI.eraseFromParent();
+    return Legalized;
+  }
+
+  return UnableToLegalize;
+}
Index: lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp
===================================================================
--- lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp
+++ lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp
@@ -917,13 +917,9 @@
     unsigned LitTyIdx = Op == G_EXTRACT ? 0 : 1;
 
     // FIXME: Doesn't handle extract of illegal sizes.
-    auto &Builder = getActionDefinitionsBuilder(Op);
-
-    // FIXME: Cleanup when G_INSERT lowering implemented.
-    if (Op == G_EXTRACT)
-      Builder.lowerIf(all(typeIs(LitTyIdx, S16), sizeIs(BigTyIdx, 32)));
-
-    Builder
+    auto &Builder = getActionDefinitionsBuilder(Op)
+      .lowerIf(all(typeIs(LitTyIdx, S16), sizeIs(BigTyIdx, 32)))
+      // FIXME: Multiples of 16 should not be legal.
       .legalIf([=](const LegalityQuery &Query) {
           const LLT BigTy = Query.Types[BigTyIdx];
           const LLT LitTy = Query.Types[LitTyIdx];
Index: test/CodeGen/AMDGPU/GlobalISel/legalize-insert.mir
===================================================================
--- test/CodeGen/AMDGPU/GlobalISel/legalize-insert.mir
+++ test/CodeGen/AMDGPU/GlobalISel/legalize-insert.mir
@@ -762,15 +762,48 @@
     ; CHECK-LABEL: name: test_insert_v2s16_s16_offset0
     ; CHECK: [[COPY:%[0-9]+]]:_(<2 x s16>) = COPY $vgpr0
     ; CHECK: [[COPY1:%[0-9]+]]:_(s32) = COPY $vgpr1
-    ; CHECK: [[TRUNC:%[0-9]+]]:_(s16) = G_TRUNC [[COPY1]](s32)
-    ; CHECK: [[INSERT:%[0-9]+]]:_(<2 x s16>) = G_INSERT [[COPY]], [[TRUNC]](s16), 0
-    ; CHECK: $vgpr0 = COPY [[INSERT]](<2 x s16>)
+    ; CHECK: [[BITCAST:%[0-9]+]]:_(s32) = G_BITCAST [[COPY]](<2 x s16>)
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 65535
+    ; CHECK: [[COPY2:%[0-9]+]]:_(s32) = COPY [[COPY1]](s32)
+    ; CHECK: [[AND:%[0-9]+]]:_(s32) = G_AND [[COPY2]], [[C]]
+    ; CHECK: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 -65536
+    ; CHECK: [[AND1:%[0-9]+]]:_(s32) = G_AND [[BITCAST]], [[C1]]
+    ; CHECK: [[OR:%[0-9]+]]:_(s32) = G_OR [[AND1]], [[AND]]
+    ; CHECK: [[BITCAST1:%[0-9]+]]:_(<2 x s16>) = G_BITCAST [[OR]](s32)
+    ; CHECK: $vgpr0 = COPY [[BITCAST1]](<2 x s16>)
     %0:_(<2 x s16>) = COPY $vgpr0
     %1:_(s32) = COPY $vgpr1
     %2:_(s16) = G_TRUNC %1
     %3:_(<2 x s16>) = G_INSERT %0, %2, 0
     $vgpr0 = COPY %3
 ...
+
+---
+name: test_insert_v2s16_s16_offset1
+body: |
+  bb.0:
+    liveins: $vgpr0, $vgpr1
+
+    ; CHECK-LABEL: name: test_insert_v2s16_s16_offset1
+    ; CHECK: [[COPY:%[0-9]+]]:_(<2 x s16>) = COPY $vgpr0
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s32) = COPY $vgpr1
+    ; CHECK: [[BITCAST:%[0-9]+]]:_(s32) = G_BITCAST [[COPY]](<2 x s16>)
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 65535
+    ; CHECK: [[COPY2:%[0-9]+]]:_(s32) = COPY [[COPY1]](s32)
+    ; CHECK: [[AND:%[0-9]+]]:_(s32) = G_AND [[COPY2]], [[C]]
+    ; CHECK: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 1
+    ; CHECK: [[SHL:%[0-9]+]]:_(s32) = G_SHL [[AND]], [[C1]](s32)
+    ; CHECK: [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 -65535
+    ; CHECK: [[AND1:%[0-9]+]]:_(s32) = G_AND [[BITCAST]], [[C2]]
+    ; CHECK: [[OR:%[0-9]+]]:_(s32) = G_OR [[AND1]], [[SHL]]
+    ; CHECK: [[BITCAST1:%[0-9]+]]:_(<2 x s16>) = G_BITCAST [[OR]](s32)
+    ; CHECK: $vgpr0 = COPY [[BITCAST1]](<2 x s16>)
+    %0:_(<2 x s16>) = COPY $vgpr0
+    %1:_(s32) = COPY $vgpr1
+    %2:_(s16) = G_TRUNC %1
+    %3:_(<2 x s16>) = G_INSERT %0, %2, 1
+    $vgpr0 = COPY %3
+...
 ---
 name: test_insert_v2s16_s16_offset16
 body: |
@@ -780,9 +813,17 @@
     ; CHECK-LABEL: name: test_insert_v2s16_s16_offset16
     ; CHECK: [[COPY:%[0-9]+]]:_(<2 x s16>) = COPY $vgpr0
     ; CHECK: [[COPY1:%[0-9]+]]:_(s32) = COPY $vgpr1
-    ; CHECK: [[TRUNC:%[0-9]+]]:_(s16) = G_TRUNC [[COPY1]](s32)
-    ; CHECK: [[INSERT:%[0-9]+]]:_(<2 x s16>) = G_INSERT [[COPY]], [[TRUNC]](s16), 16
-    ; CHECK: $vgpr0 = COPY [[INSERT]](<2 x s16>)
+    ; CHECK: [[BITCAST:%[0-9]+]]:_(s32) = G_BITCAST [[COPY]](<2 x s16>)
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 65535
+    ; CHECK: [[COPY2:%[0-9]+]]:_(s32) = COPY [[COPY1]](s32)
+    ; CHECK: [[AND:%[0-9]+]]:_(s32) = G_AND [[COPY2]], [[C]]
+    ; CHECK: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 16
+    ; CHECK: [[SHL:%[0-9]+]]:_(s32) = G_SHL [[AND]], [[C1]](s32)
+    ; CHECK: [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 -1
+    ; CHECK: [[AND1:%[0-9]+]]:_(s32) = G_AND [[BITCAST]], [[C2]]
+    ; CHECK: [[OR:%[0-9]+]]:_(s32) = G_OR [[AND1]], [[SHL]]
+    ; CHECK: [[BITCAST1:%[0-9]+]]:_(<2 x s16>) = G_BITCAST [[OR]](s32)
+    ; CHECK: $vgpr0 = COPY [[BITCAST1]](<2 x s16>)
     %0:_(<2 x s16>) = COPY $vgpr0
     %1:_(s32) = COPY $vgpr1
     %2:_(s16) = G_TRUNC %1
@@ -1247,3 +1288,104 @@
     %3:_(s64) = G_INSERT %0, %2, 48
     $vgpr0_vgpr1 = COPY %3
 ...
+---
+name: test_insert_s32_s16_offset0
+body: |
+  bb.0:
+    liveins: $vgpr0, $vgpr1
+
+    ; CHECK-LABEL: name: test_insert_s32_s16_offset0
+    ; CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY $vgpr0
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s32) = COPY $vgpr1
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 65535
+    ; CHECK: [[COPY2:%[0-9]+]]:_(s32) = COPY [[COPY1]](s32)
+    ; CHECK: [[AND:%[0-9]+]]:_(s32) = G_AND [[COPY2]], [[C]]
+    ; CHECK: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 -65536
+    ; CHECK: [[AND1:%[0-9]+]]:_(s32) = G_AND [[COPY1]], [[C1]]
+    ; CHECK: [[OR:%[0-9]+]]:_(s32) = G_OR [[AND1]], [[AND]]
+    ; CHECK: [[BITCAST:%[0-9]+]]:_(s32) = G_BITCAST [[OR]](s32)
+    ; CHECK: $vgpr0 = COPY [[BITCAST]](s32)
+    %0:_(s32) = COPY $vgpr0
+    %1:_(s32) = COPY $vgpr1
+    %2:_(s16) = G_TRUNC %1
+    %3:_(s32) = G_INSERT %1, %2, 0
+    $vgpr0 = COPY %3
+...
+
+---
+name: test_insert_s32_s16_offset1
+body: |
+  bb.0:
+    liveins: $vgpr0, $vgpr1
+
+    ; CHECK-LABEL: name: test_insert_s32_s16_offset1
+    ; CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY $vgpr0
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s32) = COPY $vgpr1
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 65535
+    ; CHECK: [[COPY2:%[0-9]+]]:_(s32) = COPY [[COPY1]](s32)
+    ; CHECK: [[AND:%[0-9]+]]:_(s32) = G_AND [[COPY2]], [[C]]
+    ; CHECK: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 1
+    ; CHECK: [[SHL:%[0-9]+]]:_(s32) = G_SHL [[AND]], [[C1]](s32)
+    ; CHECK: [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 -65535
+    ; CHECK: [[AND1:%[0-9]+]]:_(s32) = G_AND [[COPY1]], [[C2]]
+    ; CHECK: [[OR:%[0-9]+]]:_(s32) = G_OR [[AND1]], [[SHL]]
+    ; CHECK: [[BITCAST:%[0-9]+]]:_(s32) = G_BITCAST [[OR]](s32)
+    ; CHECK: $vgpr0 = COPY [[BITCAST]](s32)
+    %0:_(s32) = COPY $vgpr0
+    %1:_(s32) = COPY $vgpr1
+    %2:_(s16) = G_TRUNC %1
+    %3:_(s32) = G_INSERT %1, %2, 1
+    $vgpr0 = COPY %3
+...
+
+---
+name: test_insert_s32_s16_offset8
+body: |
+  bb.0:
+    liveins: $vgpr0, $vgpr1
+
+    ; CHECK-LABEL: name: test_insert_s32_s16_offset8
+    ; CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY $vgpr0
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s32) = COPY $vgpr1
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 65535
+    ; CHECK: [[COPY2:%[0-9]+]]:_(s32) = COPY [[COPY1]](s32)
+    ; CHECK: [[AND:%[0-9]+]]:_(s32) = G_AND [[COPY2]], [[C]]
+    ; CHECK: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 8
+    ; CHECK: [[SHL:%[0-9]+]]:_(s32) = G_SHL [[AND]], [[C1]](s32)
+    ; CHECK: [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 -65281
+    ; CHECK: [[AND1:%[0-9]+]]:_(s32) = G_AND [[COPY1]], [[C2]]
+    ; CHECK: [[OR:%[0-9]+]]:_(s32) = G_OR [[AND1]], [[SHL]]
+    ; CHECK: [[BITCAST:%[0-9]+]]:_(s32) = G_BITCAST [[OR]](s32)
+    ; CHECK: $vgpr0 = COPY [[BITCAST]](s32)
+    %0:_(s32) = COPY $vgpr0
+    %1:_(s32) = COPY $vgpr1
+    %2:_(s16) = G_TRUNC %1
+    %3:_(s32) = G_INSERT %1, %2, 8
+    $vgpr0 = COPY %3
+...
+
+---
+name: test_insert_s32_s16_offset16
+body: |
+  bb.0:
+    liveins: $vgpr0, $vgpr1
+
+    ; CHECK-LABEL: name: test_insert_s32_s16_offset16
+    ; CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY $vgpr0
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s32) = COPY $vgpr1
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 65535
+    ; CHECK: [[COPY2:%[0-9]+]]:_(s32) = COPY [[COPY1]](s32)
+    ; CHECK: [[AND:%[0-9]+]]:_(s32) = G_AND [[COPY2]], [[C]]
+    ; CHECK: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 16
+    ; CHECK: [[SHL:%[0-9]+]]:_(s32) = G_SHL [[AND]], [[C1]](s32)
+    ; CHECK: [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 -1
+    ; CHECK: [[AND1:%[0-9]+]]:_(s32) = G_AND [[COPY1]], [[C2]]
+    ; CHECK: [[OR:%[0-9]+]]:_(s32) = G_OR [[AND1]], [[SHL]]
+    ; CHECK: [[BITCAST:%[0-9]+]]:_(s32) = G_BITCAST [[OR]](s32)
+    ; CHECK: $vgpr0 = COPY [[BITCAST]](s32)
+    %0:_(s32) = COPY $vgpr0
+    %1:_(s32) = COPY $vgpr1
+    %2:_(s16) = G_TRUNC %1
+    %3:_(s32) = G_INSERT %1, %2, 16
+    $vgpr0 = COPY %3
+...