diff --git a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
--- a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
@@ -2340,9 +2340,9 @@
 bool CombinerHelper::matchConstantOp(const MachineOperand &MOP, int64_t C) {
   if (!MOP.isReg())
     return false;
-  // MIPatternMatch doesn't let us look through G_ZEXT etc.
-  auto ValAndVReg = getIConstantVRegValWithLookThrough(MOP.getReg(), MRI);
-  return ValAndVReg && ValAndVReg->Value == C;
+  auto *MI = MRI.getVRegDef(MOP.getReg());
+  auto MaybeCst = isConstantOrConstantSplatVector(*MI, MRI);
+  return MaybeCst.hasValue() && *MaybeCst == C;
 }
 
 bool CombinerHelper::replaceSingleDefInstWithOperand(MachineInstr &MI,
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/combine-mul.mir b/llvm/test/CodeGen/AArch64/GlobalISel/combine-mul.mir
--- a/llvm/test/CodeGen/AArch64/GlobalISel/combine-mul.mir
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/combine-mul.mir
@@ -31,15 +31,12 @@
 body:             |
   bb.0:
     liveins: $q0
-    ; Currently not implemented.
     ; CHECK-LABEL: name: mul_vector_by_zero
     ; CHECK: liveins: $q0
     ; CHECK-NEXT: {{  $}}
-    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(<4 x s32>) = COPY $q0
     ; CHECK-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
     ; CHECK-NEXT: [[BUILD_VECTOR:%[0-9]+]]:_(<4 x s32>) = G_BUILD_VECTOR [[C]](s32), [[C]](s32), [[C]](s32), [[C]](s32)
-    ; CHECK-NEXT: [[MUL:%[0-9]+]]:_(<4 x s32>) = G_MUL [[COPY]], [[BUILD_VECTOR]]
-    ; CHECK-NEXT: $q0 = COPY [[MUL]](<4 x s32>)
+    ; CHECK-NEXT: $q0 = COPY [[BUILD_VECTOR]](<4 x s32>)
     %0:_(<4 x s32>) = COPY $q0
     %1:_(s32) = G_CONSTANT i32 0
     %2:_(<4 x s32>) = G_BUILD_VECTOR %1(s32), %1(s32), %1(s32), %1(s32)
@@ -76,15 +73,11 @@
 body:             |
   bb.0:
     liveins: $q0
-    ; Currently not implemented.
     ; CHECK-LABEL: name: mul_vector_by_one
     ; CHECK: liveins: $q0
     ; CHECK-NEXT: {{  $}}
     ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(<4 x s32>) = COPY $q0
-    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 1
-    ; CHECK-NEXT: [[BUILD_VECTOR:%[0-9]+]]:_(<4 x s32>) = G_BUILD_VECTOR [[C]](s32), [[C]](s32), [[C]](s32), [[C]](s32)
-    ; CHECK-NEXT: [[MUL:%[0-9]+]]:_(<4 x s32>) = G_MUL [[COPY]], [[BUILD_VECTOR]]
-    ; CHECK-NEXT: $q0 = COPY [[MUL]](<4 x s32>)
+    ; CHECK-NEXT: $q0 = COPY [[COPY]](<4 x s32>)
     %0:_(<4 x s32>) = COPY $q0
     %1:_(s32) = G_CONSTANT i32 1
     %2:_(<4 x s32>) = G_BUILD_VECTOR %1(s32), %1(s32), %1(s32), %1(s32)
@@ -123,15 +116,14 @@
 body:             |
   bb.0:
     liveins: $q0
-    ; Currently not implemented.
     ; CHECK-LABEL: name: mul_vector_by_neg_one
     ; CHECK: liveins: $q0
     ; CHECK-NEXT: {{  $}}
     ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(<4 x s32>) = COPY $q0
-    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 -1
+    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
     ; CHECK-NEXT: [[BUILD_VECTOR:%[0-9]+]]:_(<4 x s32>) = G_BUILD_VECTOR [[C]](s32), [[C]](s32), [[C]](s32), [[C]](s32)
-    ; CHECK-NEXT: [[MUL:%[0-9]+]]:_(<4 x s32>) = G_MUL [[COPY]], [[BUILD_VECTOR]]
-    ; CHECK-NEXT: $q0 = COPY [[MUL]](<4 x s32>)
+    ; CHECK-NEXT: [[SUB:%[0-9]+]]:_(<4 x s32>) = G_SUB [[BUILD_VECTOR]], [[COPY]]
+    ; CHECK-NEXT: $q0 = COPY [[SUB]](<4 x s32>)
     %0:_(<4 x s32>) = COPY $q0
     %1:_(s32) = G_CONSTANT i32 -1
     %2:_(<4 x s32>) = G_BUILD_VECTOR %1(s32), %1(s32), %1(s32), %1(s32)
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-trivial-arith.mir b/llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-trivial-arith.mir
--- a/llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-trivial-arith.mir
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-trivial-arith.mir
@@ -378,3 +378,35 @@
     $w0 = COPY %rot(s32)
     RET_ReallyLR implicit $w0
 ...
+---
+name: lshr_of_vec_zero
+body:             |
+  bb.1:
+  liveins: $q0
+    ; CHECK-LABEL: name: lshr_of_vec_zero
+    ; CHECK: [[COPY:%[0-9]+]]:_(<8 x s16>) = COPY $q0
+    ; CHECK-NEXT: $q0 = COPY [[COPY]](<8 x s16>)
+    ; CHECK-NEXT: RET_ReallyLR implicit $q0
+    %0:_(<8 x s16>) = COPY $q0
+    %5:_(s16) = G_CONSTANT i16 0
+    %zero_vec:_(<8 x s16>) = G_BUILD_VECTOR %5(s16), %5(s16), %5(s16), %5(s16), %5(s16), %5(s16), %5(s16), %5(s16)
+    %shift:_(<8 x s16>) = G_LSHR %0, %zero_vec(<8 x s16>)
+    $q0 = COPY %shift(<8 x s16>)
+    RET_ReallyLR implicit $q0
+...
+---
+name: ptradd_of_vec_zero
+body:             |
+  bb.1:
+  liveins: $q0
+    ; CHECK-LABEL: name: ptradd_of_vec_zero
+    ; CHECK: [[COPY:%[0-9]+]]:_(<2 x p0>) = COPY $q0
+    ; CHECK-NEXT: $q0 = COPY [[COPY]](<2 x p0>)
+    ; CHECK-NEXT: RET_ReallyLR implicit $q0
+    %0:_(<2 x p0>) = COPY $q0
+    %5:_(s64) = G_CONSTANT i64 0
+    %zero_vec:_(<2 x s64>) = G_BUILD_VECTOR %5(s64), %5(s64)
+    %ptr:_(<2 x p0>) = G_PTR_ADD %0, %zero_vec(<2 x s64>)
+    $q0 = COPY %ptr(<2 x p0>)
+    RET_ReallyLR implicit $q0
+...