Index: llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
===================================================================
--- llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
+++ llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
@@ -2177,8 +2177,7 @@
   Register ShiftAmt = MatchInfo.second;
   Builder.setInstrAndDebugLoc(MI);
   auto TruncShiftSrc = Builder.buildTrunc(DstTy, ShiftSrc);
-  auto TruncShiftAmt = Builder.buildTrunc(DstTy, ShiftAmt);
-  Builder.buildShl(DstReg, TruncShiftSrc, TruncShiftAmt, SrcMI->getFlags());
+  Builder.buildShl(DstReg, TruncShiftSrc, ShiftAmt, SrcMI->getFlags());
   MI.eraseFromParent();
   return true;
 }
Index: llvm/test/CodeGen/AArch64/GlobalISel/combine-trunc.mir
===================================================================
--- llvm/test/CodeGen/AArch64/GlobalISel/combine-trunc.mir
+++ llvm/test/CodeGen/AArch64/GlobalISel/combine-trunc.mir
@@ -114,8 +114,7 @@
     ; CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY $w0
     ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 2
     ; CHECK: [[TRUNC:%[0-9]+]]:_(s16) = G_TRUNC [[COPY]](s32)
-    ; CHECK: [[TRUNC1:%[0-9]+]]:_(s16) = G_TRUNC [[C]](s32)
-    ; CHECK: [[SHL:%[0-9]+]]:_(s16) = G_SHL [[TRUNC]], [[TRUNC1]](s16)
+    ; CHECK: [[SHL:%[0-9]+]]:_(s16) = G_SHL [[TRUNC]], [[C]](s32)
     ; CHECK: $h0 = COPY [[SHL]](s16)
     %0:_(s32) = COPY $w0
     %1:_(s32) = G_CONSTANT i32 2
Index: llvm/test/CodeGen/AMDGPU/GlobalISel/combine-trunc-shl.mir
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/AMDGPU/GlobalISel/combine-trunc-shl.mir
@@ -0,0 +1,70 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -mtriple=amdgcn-amd-amdhsa -run-pass=amdgpu-postlegalizer-combiner -verify-machineinstrs %s -o - | FileCheck %s
+
+---
+name: trunc_s32_shl_s64_5
+legalized:       true
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $vgpr0_vgpr1
+
+    ; CHECK-LABEL: name: trunc_s32_shl_s64_5
+    ; CHECK: liveins: $vgpr0_vgpr1
+    ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $vgpr0_vgpr1
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 1
+    ; CHECK: [[TRUNC:%[0-9]+]]:_(s32) = G_TRUNC [[COPY]](s64)
+    ; CHECK: [[SHL:%[0-9]+]]:_(s32) = G_SHL [[TRUNC]], [[C]](s32)
+    ; CHECK: $vgpr0 = COPY [[SHL]](s32)
+    %0:_(s64) = COPY $vgpr0_vgpr1
+    %1:_(s32) = G_CONSTANT i32 1
+    %2:_(s64) = G_SHL %0:_, %1
+    %3:_(s32) = G_TRUNC %2
+    $vgpr0 = COPY %3
+...
+
+---
+name: trunc_s16_shl_s32_5
+legalized:       true
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $vgpr0
+
+    ; CHECK-LABEL: name: trunc_s16_shl_s32_5
+    ; CHECK: liveins: $vgpr0
+    ; CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY $vgpr0
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 1
+    ; CHECK: [[SHL:%[0-9]+]]:_(s32) = G_SHL [[COPY]], [[C]](s32)
+    ; CHECK: [[TRUNC:%[0-9]+]]:_(s16) = G_TRUNC [[SHL]](s32)
+    ; CHECK: S_ENDPGM 0, implicit [[TRUNC]](s16)
+    %0:_(s32) = COPY $vgpr0
+    %1:_(s32) = G_CONSTANT i32 1
+    %2:_(s32) = G_SHL %0:_, %1
+    %3:_(s16) = G_TRUNC %2
+    S_ENDPGM 0, implicit %3
+
+...
+
+---
+name: trunc_s16_shl_s64_5
+legalized:       true
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $vgpr0_vgpr1
+
+    ; CHECK-LABEL: name: trunc_s16_shl_s64_5
+    ; CHECK: liveins: $vgpr0_vgpr1
+    ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $vgpr0_vgpr1
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 1
+    ; CHECK: [[SHL:%[0-9]+]]:_(s64) = G_SHL [[COPY]], [[C]](s32)
+    ; CHECK: [[TRUNC:%[0-9]+]]:_(s16) = G_TRUNC [[SHL]](s64)
+    ; CHECK: S_ENDPGM 0, implicit [[TRUNC]](s16)
+    %0:_(s64) = COPY $vgpr0_vgpr1
+    %1:_(s32) = G_CONSTANT i32 1
+    %2:_(s64) = G_SHL %0:_, %1
+    %3:_(s16) = G_TRUNC %2
+    S_ENDPGM 0, implicit %3
+
+...