Index: llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h
===================================================================
--- llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h
+++ llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h
@@ -316,6 +316,9 @@
   bool matchCombineAnyExtTrunc(MachineInstr &MI, Register &Reg);
   bool applyCombineAnyExtTrunc(MachineInstr &MI, Register &Reg);
 
+  /// Transform zext(trunc(x)) to x.
+  bool matchCombineZextTrunc(MachineInstr &MI, Register &Reg);
+
   /// Transform [asz]ext([asz]ext(x)) to [asz]ext x.
   bool matchCombineExtOfExt(MachineInstr &MI,
                             std::tuple<Register, unsigned> &MatchInfo);
Index: llvm/include/llvm/Target/GlobalISel/Combine.td
===================================================================
--- llvm/include/llvm/Target/GlobalISel/Combine.td
+++ llvm/include/llvm/Target/GlobalISel/Combine.td
@@ -426,6 +426,16 @@
   (apply [{ return Helper.applyCombineAnyExtTrunc(*${root}, ${matchinfo}); }])
 >;
 
+// Fold (zext (trunc x)) -> x if the source type is same as the destination type
+// and truncated bits are known to be zero.
+def zext_trunc_fold_matchinfo : GIDefMatchData<"Register">;
+def zext_trunc_fold: GICombineRule <
+  (defs root:$root, zext_trunc_fold_matchinfo:$matchinfo),
+  (match (wip_match_opcode G_ZEXT):$root,
+         [{ return Helper.matchCombineZextTrunc(*${root}, ${matchinfo}); }]),
+  (apply [{ return Helper.replaceSingleDefInstWithReg(*${root}, ${matchinfo}); }])
+>;
+
 // Fold ([asz]ext ([asz]ext x)) -> ([asz]ext x).
 def ext_ext_fold_matchinfo : GIDefMatchData<"std::tuple<Register, unsigned>">;
 def ext_ext_fold: GICombineRule <
@@ -575,7 +585,8 @@
 def const_combines : GICombineGroup<[constant_fp_op, const_ptradd_to_i2p]>;
 
 def known_bits_simplifications : GICombineGroup<[
-  redundant_and, redundant_sext_inreg, redundant_or, urem_pow2_to_mask]>;
+  redundant_and, redundant_sext_inreg, redundant_or, urem_pow2_to_mask,
+  zext_trunc_fold]>;
 
 def width_reduction_combines : GICombineGroup<[reduce_shl_of_extend]>;
 
Index: llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
===================================================================
--- llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
+++ llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
@@ -2301,6 +2301,20 @@
   return true;
 }
 
+bool CombinerHelper::matchCombineZextTrunc(MachineInstr &MI, Register &Reg) {
+  assert(MI.getOpcode() == TargetOpcode::G_ZEXT && "Expected a G_ZEXT");
+  Register DstReg = MI.getOperand(0).getReg();
+  Register SrcReg = MI.getOperand(1).getReg();
+  LLT DstTy = MRI.getType(DstReg);
+  if (mi_match(SrcReg, MRI,
+               m_GTrunc(m_all_of(m_Reg(Reg), m_SpecificType(DstTy))))) {
+    unsigned DstSize = DstTy.getScalarSizeInBits();
+    unsigned SrcSize = MRI.getType(SrcReg).getScalarSizeInBits();
+    return KB->getKnownBits(Reg).countMinLeadingZeros() >= DstSize - SrcSize;
+  }
+  return false;
+}
+
 bool CombinerHelper::matchCombineExtOfExt(
     MachineInstr &MI, std::tuple<Register, unsigned> &MatchInfo) {
   assert((MI.getOpcode() == TargetOpcode::G_ANYEXT ||
Index: llvm/test/CodeGen/AMDGPU/GlobalISel/combine-zext-trunc.mir
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/AMDGPU/GlobalISel/combine-zext-trunc.mir
@@ -0,0 +1,198 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -mtriple=amdgcn-mesa-mesa3d -mcpu=gfx1010 -run-pass=amdgpu-prelegalizer-combiner -verify-machineinstrs %s -o - | FileCheck -check-prefix=GCN %s
+
+---
+name: zext_trunc_s32_s16_s32
+tracksRegLiveness: true
+body:|
+  bb.0:
+    liveins: $vgpr0
+
+    ; GCN-LABEL: name: zext_trunc_s32_s16_s32
+    ; GCN: liveins: $vgpr0
+    ; GCN: %var:_(s32) = COPY $vgpr0
+    ; GCN: %c3FFF:_(s32) = G_CONSTANT i32 16383
+    ; GCN: %low_bits:_(s32) = G_AND %var, %c3FFF
+    ; GCN: $vgpr0 = COPY %low_bits(s32)
+    %var:_(s32) = COPY $vgpr0
+    %c3FFF:_(s32) = G_CONSTANT i32 16383
+    %low_bits:_(s32) = G_AND %var, %c3FFF
+    %trunc:_(s16) = G_TRUNC %low_bits(s32)
+    %zext:_(s32) = G_ZEXT %trunc(s16)
+    $vgpr0 = COPY %zext(s32)
+...
+
+---
+name: zext_trunc_s32_s16_s32_unknown_high_bits
+tracksRegLiveness: true
+body:|
+  bb.0:
+    liveins: $vgpr0
+
+    ; GCN-LABEL: name: zext_trunc_s32_s16_s32_unknown_high_bits
+    ; GCN: liveins: $vgpr0
+    ; GCN: %var:_(s32) = COPY $vgpr0
+    ; GCN: %cFFFFF:_(s32) = G_CONSTANT i32 1048575
+    ; GCN: %low_bits:_(s32) = G_AND %var, %cFFFFF
+    ; GCN: %trunc:_(s16) = G_TRUNC %low_bits(s32)
+    ; GCN: %zext:_(s32) = G_ZEXT %trunc(s16)
+    ; GCN: $vgpr0 = COPY %zext(s32)
+    %var:_(s32) = COPY $vgpr0
+    %cFFFFF:_(s32) = G_CONSTANT i32 1048575
+    %low_bits:_(s32) = G_AND %var, %cFFFFF
+    %trunc:_(s16) = G_TRUNC %low_bits(s32)
+    %zext:_(s32) = G_ZEXT %trunc(s16)
+    $vgpr0 = COPY %zext(s32)
+...
+
+---
+name: zext_trunc_s64_s16_s32
+tracksRegLiveness: true
+body:|
+  bb.0:
+    liveins: $vgpr0_vgpr1
+
+    ; GCN-LABEL: name: zext_trunc_s64_s16_s32
+    ; GCN: liveins: $vgpr0_vgpr1
+    ; GCN: %var:_(s64) = COPY $vgpr0_vgpr1
+    ; GCN: %c3FFF:_(s64) = G_CONSTANT i64 16383
+    ; GCN: %low_bits:_(s64) = G_AND %var, %c3FFF
+    ; GCN: %trunc:_(s16) = G_TRUNC %low_bits(s64)
+    ; GCN: %zext:_(s32) = G_ZEXT %trunc(s16)
+    ; GCN: $vgpr0 = COPY %zext(s32)
+    %var:_(s64) = COPY $vgpr0_vgpr1
+    %c3FFF:_(s64) = G_CONSTANT i64 16383
+    %low_bits:_(s64) = G_AND %var, %c3FFF
+    %trunc:_(s16) = G_TRUNC %low_bits(s64)
+    %zext:_(s32) = G_ZEXT %trunc(s16)
+    $vgpr0 = COPY %zext(s32)
+...
+
+---
+name: zext_trunc_s32_s16_s64
+tracksRegLiveness: true
+body:|
+  bb.0:
+    liveins: $vgpr0
+
+    ; GCN-LABEL: name: zext_trunc_s32_s16_s64
+    ; GCN: liveins: $vgpr0
+    ; GCN: %var:_(s32) = COPY $vgpr0
+    ; GCN: %c3FFF:_(s32) = G_CONSTANT i32 16383
+    ; GCN: %low_bits:_(s32) = G_AND %var, %c3FFF
+    ; GCN: %trunc:_(s16) = G_TRUNC %low_bits(s32)
+    ; GCN: %zext:_(s64) = G_ZEXT %trunc(s16)
+    ; GCN: $vgpr0_vgpr1 = COPY %zext(s64)
+    %var:_(s32) = COPY $vgpr0
+    %c3FFF:_(s32) = G_CONSTANT i32 16383
+    %low_bits:_(s32) = G_AND %var, %c3FFF
+    %trunc:_(s16) = G_TRUNC %low_bits(s32)
+    %zext:_(s64) = G_ZEXT %trunc(s16)
+    $vgpr0_vgpr1 = COPY %zext(s64)
+...
+
+---
+name: zext_trunc_v2s32_v2s16_v2s32
+tracksRegLiveness: true
+body:|
+  bb.0:
+    liveins: $vgpr0_vgpr1
+
+    ; GCN-LABEL: name: zext_trunc_v2s32_v2s16_v2s32
+    ; GCN: liveins: $vgpr0_vgpr1
+    ; GCN: %var:_(<2 x s32>) = COPY $vgpr0_vgpr1
+    ; GCN: %c3FFF:_(s32) = G_CONSTANT i32 16383
+    ; GCN: %c7FFF:_(s32) = G_CONSTANT i32 32767
+    ; GCN: %c:_(<2 x s32>) = G_BUILD_VECTOR %c3FFF(s32), %c7FFF(s32)
+    ; GCN: %low_bits:_(<2 x s32>) = G_AND %var, %c
+    ; GCN: $vgpr0_vgpr1 = COPY %low_bits(<2 x s32>)
+    %var:_(<2 x s32>) = COPY $vgpr0_vgpr1
+    %c3FFF:_(s32) = G_CONSTANT i32 16383
+    %c7FFF:_(s32) = G_CONSTANT i32 32767
+    %c:_(<2 x s32>) = G_BUILD_VECTOR %c3FFF(s32), %c7FFF(s32)
+    %low_bits:_(<2 x s32>) = G_AND %var, %c
+    %trunc:_(<2 x s16>) = G_TRUNC %low_bits(<2 x s32>)
+    %zext:_(<2 x s32>) = G_ZEXT %trunc(<2 x s16>)
+    $vgpr0_vgpr1 = COPY %zext(<2 x s32>)
+...
+
+---
+name: zext_trunc_v2s32_v2s16_v2s32_unknown_high_bits
+tracksRegLiveness: true
+body:|
+  bb.0:
+    liveins: $vgpr0_vgpr1
+
+    ; GCN-LABEL: name: zext_trunc_v2s32_v2s16_v2s32_unknown_high_bits
+    ; GCN: liveins: $vgpr0_vgpr1
+    ; GCN: %var:_(<2 x s32>) = COPY $vgpr0_vgpr1
+    ; GCN: %cFFFFF:_(s32) = G_CONSTANT i32 1048575
+    ; GCN: %c7FFF:_(s32) = G_CONSTANT i32 32767
+    ; GCN: %c:_(<2 x s32>) = G_BUILD_VECTOR %cFFFFF(s32), %c7FFF(s32)
+    ; GCN: %low_bits:_(<2 x s32>) = G_AND %var, %c
+    ; GCN: %trunc:_(<2 x s16>) = G_TRUNC %low_bits(<2 x s32>)
+    ; GCN: %zext:_(<2 x s32>) = G_ZEXT %trunc(<2 x s16>)
+    ; GCN: $vgpr0_vgpr1 = COPY %zext(<2 x s32>)
+    %var:_(<2 x s32>) = COPY $vgpr0_vgpr1
+    %cFFFFF:_(s32) = G_CONSTANT i32 1048575
+    %c7FFF:_(s32) = G_CONSTANT i32 32767
+    %c:_(<2 x s32>) = G_BUILD_VECTOR %cFFFFF(s32), %c7FFF(s32)
+    %low_bits:_(<2 x s32>) = G_AND %var, %c
+    %trunc:_(<2 x s16>) = G_TRUNC %low_bits(<2 x s32>)
+    %zext:_(<2 x s32>) = G_ZEXT %trunc(<2 x s16>)
+    $vgpr0_vgpr1 = COPY %zext(<2 x s32>)
+...
+
+---
+name: zext_trunc_v2s64_v2s16_v2s32
+tracksRegLiveness: true
+body:|
+  bb.0:
+    liveins: $vgpr0_vgpr1_vgpr2_vgpr3
+
+    ; GCN-LABEL: name: zext_trunc_v2s64_v2s16_v2s32
+    ; GCN: liveins: $vgpr0_vgpr1_vgpr2_vgpr3
+    ; GCN: %var:_(<2 x s64>) = COPY $vgpr0_vgpr1_vgpr2_vgpr3
+    ; GCN: %c3FFF:_(s64) = G_CONSTANT i64 16383
+    ; GCN: %c7FFF:_(s64) = G_CONSTANT i64 32767
+    ; GCN: %c:_(<2 x s64>) = G_BUILD_VECTOR %c3FFF(s64), %c7FFF(s64)
+    ; GCN: %low_bits:_(<2 x s64>) = G_AND %var, %c
+    ; GCN: %trunc:_(<2 x s16>) = G_TRUNC %low_bits(<2 x s64>)
+    ; GCN: %zext:_(<2 x s32>) = G_ZEXT %trunc(<2 x s16>)
+    ; GCN: $vgpr0_vgpr1 = COPY %zext(<2 x s32>)
+    %var:_(<2 x s64>) = COPY $vgpr0_vgpr1_vgpr2_vgpr3
+    %c3FFF:_(s64) = G_CONSTANT i64 16383
+    %c7FFF:_(s64) = G_CONSTANT i64 32767
+    %c:_(<2 x s64>) = G_BUILD_VECTOR %c3FFF(s64), %c7FFF(s64)
+    %low_bits:_(<2 x s64>) = G_AND %var, %c
+    %trunc:_(<2 x s16>) = G_TRUNC %low_bits(<2 x s64>)
+    %zext:_(<2 x s32>) = G_ZEXT %trunc(<2 x s16>)
+    $vgpr0_vgpr1 = COPY %zext(<2 x s32>)
+...
+
+---
+name: zext_trunc_v2s32_v2s16_v2s64
+tracksRegLiveness: true
+body:|
+  bb.0:
+    liveins: $vgpr0_vgpr1
+
+    ; GCN-LABEL: name: zext_trunc_v2s32_v2s16_v2s64
+    ; GCN: liveins: $vgpr0_vgpr1
+    ; GCN: %var:_(<2 x s32>) = COPY $vgpr0_vgpr1
+    ; GCN: %c3FFF:_(s32) = G_CONSTANT i32 16383
+    ; GCN: %c7FFF:_(s32) = G_CONSTANT i32 32767
+    ; GCN: %c:_(<2 x s32>) = G_BUILD_VECTOR %c3FFF(s32), %c7FFF(s32)
+    ; GCN: %low_bits:_(<2 x s32>) = G_AND %var, %c
+    ; GCN: %trunc:_(<2 x s16>) = G_TRUNC %low_bits(<2 x s32>)
+    ; GCN: %zext:_(<2 x s64>) = G_ZEXT %trunc(<2 x s16>)
+    ; GCN: $vgpr0_vgpr1_vgpr2_vgpr3 = COPY %zext(<2 x s64>)
+    %var:_(<2 x s32>) = COPY $vgpr0_vgpr1
+    %c3FFF:_(s32) = G_CONSTANT i32 16383
+    %c7FFF:_(s32) = G_CONSTANT i32 32767
+    %c:_(<2 x s32>) = G_BUILD_VECTOR %c3FFF(s32), %c7FFF(s32)
+    %low_bits:_(<2 x s32>) = G_AND %var, %c
+    %trunc:_(<2 x s16>) = G_TRUNC %low_bits(<2 x s32>)
+    %zext:_(<2 x s64>) = G_ZEXT %trunc(<2 x s16>)
+    $vgpr0_vgpr1_vgpr2_vgpr3 = COPY %zext(<2 x s64>)
+...
Index: llvm/test/CodeGen/AMDGPU/GlobalISel/shl-ext-reduce.ll
===================================================================
--- llvm/test/CodeGen/AMDGPU/GlobalISel/shl-ext-reduce.ll
+++ llvm/test/CodeGen/AMDGPU/GlobalISel/shl-ext-reduce.ll
@@ -404,18 +404,14 @@
 ; GFX8:       ; %bb.0:
 ; GFX8-NEXT:    s_and_b32 s0, s0, 0xffff
 ; GFX8-NEXT:    s_and_b32 s0, s0, 0x3fff
-; GFX8-NEXT:    s_bfe_u32 s1, 2, 0x100000
-; GFX8-NEXT:    s_lshl_b32 s0, s0, s1
-; GFX8-NEXT:    s_bfe_u32 s0, s0, 0x100000
+; GFX8-NEXT:    s_lshl_b32 s0, s0, 2
 ; GFX8-NEXT:    ; return to shader part epilog
 ;
 ; GFX9-LABEL: s_shl_i32_zext_i16:
 ; GFX9:       ; %bb.0:
 ; GFX9-NEXT:    s_and_b32 s0, s0, 0xffff
 ; GFX9-NEXT:    s_and_b32 s0, s0, 0x3fff
-; GFX9-NEXT:    s_bfe_u32 s1, 2, 0x100000
-; GFX9-NEXT:    s_lshl_b32 s0, s0, s1
-; GFX9-NEXT:    s_bfe_u32 s0, s0, 0x100000
+; GFX9-NEXT:    s_lshl_b32 s0, s0, 2
 ; GFX9-NEXT:    ; return to shader part epilog
   %and = and i16 %x, 16383
   %ext = zext i16 %and to i32
@@ -468,13 +464,10 @@
 ; GFX8-LABEL: s_shl_v2i32_zext_v2i16:
 ; GFX8:       ; %bb.0:
 ; GFX8-NEXT:    s_movk_i32 s2, 0x3fff
-; GFX8-NEXT:    s_mov_b32 s4, 0xffff
 ; GFX8-NEXT:    s_lshr_b32 s1, s0, 16
 ; GFX8-NEXT:    s_mov_b32 s3, s2
-; GFX8-NEXT:    s_and_b32 s0, s0, s4
+; GFX8-NEXT:    s_and_b32 s0, s0, 0xffff
 ; GFX8-NEXT:    s_and_b64 s[0:1], s[0:1], s[2:3]
-; GFX8-NEXT:    s_mov_b32 s5, s4
-; GFX8-NEXT:    s_and_b64 s[0:1], s[0:1], s[4:5]
 ; GFX8-NEXT:    s_lshl_b32 s0, s0, 2
 ; GFX8-NEXT:    s_lshl_b32 s1, s1, 2
 ; GFX8-NEXT:    ; return to shader part epilog