diff --git a/llvm/lib/Target/AArch64/GISel/AArch64PostLegalizerLowering.cpp b/llvm/lib/Target/AArch64/GISel/AArch64PostLegalizerLowering.cpp
--- a/llvm/lib/Target/AArch64/GISel/AArch64PostLegalizerLowering.cpp
+++ b/llvm/lib/Target/AArch64/GISel/AArch64PostLegalizerLowering.cpp
@@ -29,6 +29,7 @@
 #include "llvm/CodeGen/GlobalISel/Combiner.h"
 #include "llvm/CodeGen/GlobalISel/CombinerHelper.h"
 #include "llvm/CodeGen/GlobalISel/CombinerInfo.h"
+#include "llvm/CodeGen/GlobalISel/GenericMachineInstrs.h"
 #include "llvm/CodeGen/GlobalISel/MIPatternMatch.h"
 #include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
 #include "llvm/CodeGen/GlobalISel/Utils.h"
@@ -370,22 +371,60 @@
   return false;
 }
 
+// Check if an EXT instruction can handle the shuffle mask when the vector
+// sources of the shuffle are the same.
+static bool isSingletonExtMask(ArrayRef<int> M, LLT Ty) {
+  unsigned NumElts = Ty.getNumElements();
+
+  // Assume that the first shuffle index is not UNDEF.  Fail if it is.
+  if (M[0] < 0)
+    return false;
+
+  // If this is a VEXT shuffle, the immediate value is the index of the first
+  // element.  The other shuffle indices must be the successive elements after
+  // the first one.
+  unsigned ExpectedElt = M[0];
+  for (unsigned I = 1; I < NumElts; ++I) {
+    // Increment the expected index.  If it wraps around, just follow it
+    // back to index zero and keep going.
+    ++ExpectedElt;
+    if (ExpectedElt == NumElts)
+      ExpectedElt = 0;
+
+    if (M[I] < 0)
+      continue; // Ignore UNDEF indices.
+    if (ExpectedElt != static_cast<unsigned>(M[I]))
+      return false;
+  }
+
+  return true;
+}
+
 static bool matchEXT(MachineInstr &MI, MachineRegisterInfo &MRI,
                      ShuffleVectorPseudo &MatchInfo) {
   assert(MI.getOpcode() == TargetOpcode::G_SHUFFLE_VECTOR);
   Register Dst = MI.getOperand(0).getReg();
-  auto ExtInfo = getExtMask(MI.getOperand(3).getShuffleMask(),
-                            MRI.getType(Dst).getNumElements());
-  if (!ExtInfo)
-    return false;
-  bool ReverseExt;
-  uint64_t Imm;
-  std::tie(ReverseExt, Imm) = *ExtInfo;
+  LLT DstTy = MRI.getType(Dst);
   Register V1 = MI.getOperand(1).getReg();
   Register V2 = MI.getOperand(2).getReg();
+  auto Mask = MI.getOperand(3).getShuffleMask();
+  uint64_t Imm;
+  auto ExtInfo = getExtMask(Mask, DstTy.getNumElements());
+  uint64_t ExtFactor = MRI.getType(V1).getScalarSizeInBits() / 8;
+
+  if (!ExtInfo) {
+    if (!getOpcodeDef<GImplicitDef>(V2, MRI) ||
+        !isSingletonExtMask(Mask, DstTy))
+      return false;
+
+    Imm = Mask[0] * ExtFactor;
+    MatchInfo = ShuffleVectorPseudo(AArch64::G_EXT, Dst, {V1, V1, Imm});
+    return true;
+  }
+  bool ReverseExt;
+  std::tie(ReverseExt, Imm) = *ExtInfo;
   if (ReverseExt)
     std::swap(V1, V2);
-  uint64_t ExtFactor = MRI.getType(V1).getScalarSizeInBits() / 8;
   Imm *= ExtFactor;
   MatchInfo = ShuffleVectorPseudo(AArch64::G_EXT, Dst, {V1, V2, Imm});
   return true;
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/postlegalizer-lowering-ext.mir b/llvm/test/CodeGen/AArch64/GlobalISel/postlegalizer-lowering-ext.mir
--- a/llvm/test/CodeGen/AArch64/GlobalISel/postlegalizer-lowering-ext.mir
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/postlegalizer-lowering-ext.mir
@@ -267,3 +267,69 @@
     $q0 = COPY %shuf(<8 x s16>)
     RET_ReallyLR implicit $q0
 ...
+---
+name:            v2s64_singleton_ext
+alignment:       4
+legalized:       true
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $q0
+    ; CHECK-LABEL: name: v2s64_singleton_ext
+    ; CHECK: liveins: $q0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: %v1:_(<2 x s64>) = COPY $q0
+    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 8
+    ; CHECK-NEXT: %shuf:_(<2 x s64>) = G_EXT %v1, %v1, [[C]](s32)
+    ; CHECK-NEXT: $q0 = COPY %shuf(<2 x s64>)
+    ; CHECK-NEXT: RET_ReallyLR implicit $q0
+    %v1:_(<2 x s64>) = COPY $q0
+    %v2:_(<2 x s64>) = G_IMPLICIT_DEF
+    %shuf:_(<2 x s64>) = G_SHUFFLE_VECTOR %v1(<2 x s64>), %v2, shufflemask(1, 0)
+    $q0 = COPY %shuf(<2 x s64>)
+    RET_ReallyLR implicit $q0
+...
+---
+name:            v2s64_singleton_ext_all_undef
+alignment:       4
+legalized:       true
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $q0
+    ; CHECK-LABEL: name: v2s64_singleton_ext_all_undef
+    ; CHECK: liveins: $q0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: %v1:_(<2 x s64>) = COPY $q0
+    ; CHECK-NEXT: %v2:_(<2 x s64>) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: %shuf:_(<2 x s64>) = G_ZIP2 %v1, %v2
+    ; CHECK-NEXT: $q0 = COPY %shuf(<2 x s64>)
+    ; CHECK-NEXT: RET_ReallyLR implicit $q0
+    %v1:_(<2 x s64>) = COPY $q0
+    %v2:_(<2 x s64>) = G_IMPLICIT_DEF
+    %shuf:_(<2 x s64>) = G_SHUFFLE_VECTOR %v1(<2 x s64>), %v2, shufflemask(undef, undef)
+    $q0 = COPY %shuf(<2 x s64>)
+    RET_ReallyLR implicit $q0
+...
+---
+name:            v2s64_singleton_ext_same
+alignment:       4
+legalized:       true
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $q0
+    ; CHECK-LABEL: name: v2s64_singleton_ext_same
+    ; CHECK: liveins: $q0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: %v1:_(<2 x s64>) = COPY $q0
+    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s64) = G_CONSTANT i64 1
+    ; CHECK-NEXT: %shuf:_(<2 x s64>) = G_DUPLANE64 %v1, [[C]](s64)
+    ; CHECK-NEXT: $q0 = COPY %shuf(<2 x s64>)
+    ; CHECK-NEXT: RET_ReallyLR implicit $q0
+    %v1:_(<2 x s64>) = COPY $q0
+    %v2:_(<2 x s64>) = G_IMPLICIT_DEF
+    %shuf:_(<2 x s64>) = G_SHUFFLE_VECTOR %v1(<2 x s64>), %v2, shufflemask(1, 1)
+    $q0 = COPY %shuf(<2 x s64>)
+    RET_ReallyLR implicit $q0
+...
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/postlegalizer-lowering-uzp.mir b/llvm/test/CodeGen/AArch64/GlobalISel/postlegalizer-lowering-uzp.mir
--- a/llvm/test/CodeGen/AArch64/GlobalISel/postlegalizer-lowering-uzp.mir
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/postlegalizer-lowering-uzp.mir
@@ -16,11 +16,12 @@
 
     ; CHECK-LABEL: name: uzp1_v4s32
     ; CHECK: liveins: $q0, $q1
-    ; CHECK: [[COPY:%[0-9]+]]:_(<4 x s32>) = COPY $q0
-    ; CHECK: [[COPY1:%[0-9]+]]:_(<4 x s32>) = COPY $q1
-    ; CHECK: [[UZP1_:%[0-9]+]]:_(<4 x s32>) = G_UZP1 [[COPY]], [[COPY1]]
-    ; CHECK: $q0 = COPY [[UZP1_]](<4 x s32>)
-    ; CHECK: RET_ReallyLR implicit $q0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(<4 x s32>) = COPY $q0
+    ; CHECK-NEXT: [[COPY1:%[0-9]+]]:_(<4 x s32>) = COPY $q1
+    ; CHECK-NEXT: [[UZP1_:%[0-9]+]]:_(<4 x s32>) = G_UZP1 [[COPY]], [[COPY1]]
+    ; CHECK-NEXT: $q0 = COPY [[UZP1_]](<4 x s32>)
+    ; CHECK-NEXT: RET_ReallyLR implicit $q0
     %0:_(<4 x s32>) = COPY $q0
     %1:_(<4 x s32>) = COPY $q1
     %2:_(<4 x s32>) = G_SHUFFLE_VECTOR %0(<4 x s32>), %1, shufflemask(0, 2, 4, 6)
@@ -38,15 +39,16 @@
 
     ; CHECK-LABEL: name: uzp2_v4s32
     ; CHECK: liveins: $q0, $q1
-    ; CHECK: [[COPY:%[0-9]+]]:_(<4 x s32>) = COPY $q0
-    ; CHECK: [[COPY1:%[0-9]+]]:_(<4 x s32>) = COPY $q1
-    ; CHECK: [[UZP2_:%[0-9]+]]:_(<4 x s32>) = G_UZP2 [[COPY]], [[UZP2_]]
-    ; CHECK: $q0 = COPY [[UZP2_]](<4 x s32>)
-    ; CHECK: RET_ReallyLR implicit $q0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(<4 x s32>) = COPY $q0
+    ; CHECK-NEXT: [[COPY1:%[0-9]+]]:_(<4 x s32>) = COPY $q1
+    ; CHECK-NEXT: [[UZP2_:%[0-9]+]]:_(<4 x s32>) = G_UZP2 [[COPY]], [[COPY1]]
+    ; CHECK-NEXT: $q0 = COPY [[UZP2_]](<4 x s32>)
+    ; CHECK-NEXT: RET_ReallyLR implicit $q0
     %0:_(<4 x s32>) = COPY $q0
     %1:_(<4 x s32>) = COPY $q1
-    %1:_(<4 x s32>) = G_SHUFFLE_VECTOR %0(<4 x s32>), %1, shufflemask(1, 3, 5, 7)
-    $q0 = COPY %1(<4 x s32>)
+    %2:_(<4 x s32>) = G_SHUFFLE_VECTOR %0(<4 x s32>), %1, shufflemask(1, 3, 5, 7)
+    $q0 = COPY %2(<4 x s32>)
     RET_ReallyLR implicit $q0
 
 ...
@@ -62,11 +64,12 @@
 
     ; CHECK-LABEL: name: no_uzp1
     ; CHECK: liveins: $q0, $q1
-    ; CHECK: [[COPY:%[0-9]+]]:_(<4 x s32>) = COPY $q0
-    ; CHECK: [[COPY1:%[0-9]+]]:_(<4 x s32>) = COPY $q1
-    ; CHECK: [[SHUF:%[0-9]+]]:_(<4 x s32>) = G_SHUFFLE_VECTOR [[COPY]](<4 x s32>), [[COPY1]], shufflemask(0, 1, 4, 6)
-    ; CHECK: $q0 = COPY [[SHUF]](<4 x s32>)
-    ; CHECK: RET_ReallyLR implicit $q0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(<4 x s32>) = COPY $q0
+    ; CHECK-NEXT: [[COPY1:%[0-9]+]]:_(<4 x s32>) = COPY $q1
+    ; CHECK-NEXT: [[SHUF:%[0-9]+]]:_(<4 x s32>) = G_SHUFFLE_VECTOR [[COPY]](<4 x s32>), [[COPY1]], shufflemask(0, 1, 4, 6)
+    ; CHECK-NEXT: $q0 = COPY [[SHUF]](<4 x s32>)
+    ; CHECK-NEXT: RET_ReallyLR implicit $q0
     %0:_(<4 x s32>) = COPY $q0
     %1:_(<4 x s32>) = COPY $q1
     %2:_(<4 x s32>) = G_SHUFFLE_VECTOR %0(<4 x s32>), %1, shufflemask(0, 1, 4, 6)
@@ -86,11 +89,12 @@
 
     ; CHECK-LABEL: name: no_uzp2
     ; CHECK: liveins: $q0, $q1
-    ; CHECK: [[COPY:%[0-9]+]]:_(<4 x s32>) = COPY $q0
-    ; CHECK: [[COPY1:%[0-9]+]]:_(<4 x s32>) = COPY $q1
-    ; CHECK: [[SHUF:%[0-9]+]]:_(<4 x s32>) = G_SHUFFLE_VECTOR [[COPY]](<4 x s32>), [[COPY1]], shufflemask(1, 4, 5, 7)
-    ; CHECK: $q0 = COPY [[SHUF]](<4 x s32>)
-    ; CHECK: RET_ReallyLR implicit $q0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(<4 x s32>) = COPY $q0
+    ; CHECK-NEXT: [[COPY1:%[0-9]+]]:_(<4 x s32>) = COPY $q1
+    ; CHECK-NEXT: [[SHUF:%[0-9]+]]:_(<4 x s32>) = G_SHUFFLE_VECTOR [[COPY]](<4 x s32>), [[COPY1]], shufflemask(1, 4, 5, 7)
+    ; CHECK-NEXT: $q0 = COPY [[SHUF]](<4 x s32>)
+    ; CHECK-NEXT: RET_ReallyLR implicit $q0
     %0:_(<4 x s32>) = COPY $q0
     %1:_(<4 x s32>) = COPY $q1
     %2:_(<4 x s32>) = G_SHUFFLE_VECTOR %0(<4 x s32>), %1, shufflemask(1, 4, 5, 7)
@@ -110,11 +114,12 @@
 
     ; CHECK-LABEL: name: uzp1_undef
     ; CHECK: liveins: $q0, $q1
-    ; CHECK: [[COPY:%[0-9]+]]:_(<4 x s32>) = COPY $q0
-    ; CHECK: [[COPY1:%[0-9]+]]:_(<4 x s32>) = COPY $q1
-    ; CHECK: [[UZP1_:%[0-9]+]]:_(<4 x s32>) = G_UZP1 [[COPY]], [[COPY1]]
-    ; CHECK: $q0 = COPY [[UZP1_]](<4 x s32>)
-    ; CHECK: RET_ReallyLR implicit $q0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(<4 x s32>) = COPY $q0
+    ; CHECK-NEXT: [[COPY1:%[0-9]+]]:_(<4 x s32>) = COPY $q1
+    ; CHECK-NEXT: [[UZP1_:%[0-9]+]]:_(<4 x s32>) = G_UZP1 [[COPY]], [[COPY1]]
+    ; CHECK-NEXT: $q0 = COPY [[UZP1_]](<4 x s32>)
+    ; CHECK-NEXT: RET_ReallyLR implicit $q0
     %0:_(<4 x s32>) = COPY $q0
     %1:_(<4 x s32>) = COPY $q1
     %2:_(<4 x s32>) = G_SHUFFLE_VECTOR %0(<4 x s32>), %1, shufflemask(0, -1, 4, 6)
@@ -134,13 +139,14 @@
 
     ; CHECK-LABEL: name: uzp2_undef
     ; CHECK: liveins: $q0, $q1
-    ; CHECK: [[COPY:%[0-9]+]]:_(<4 x s32>) = COPY $q0
-    ; CHECK: [[COPY1:%[0-9]+]]:_(<4 x s32>) = COPY $q1
-    ; CHECK: [[UZP2_:%[0-9]+]]:_(<4 x s32>) = G_UZP2 [[COPY]], [[UZP2_]]
-    ; CHECK: $q0 = COPY [[UZP2_]](<4 x s32>)
-    ; CHECK: RET_ReallyLR implicit $q0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(<4 x s32>) = COPY $q0
+    ; CHECK-NEXT: [[COPY1:%[0-9]+]]:_(<4 x s32>) = COPY $q1
+    ; CHECK-NEXT: [[UZP2_:%[0-9]+]]:_(<4 x s32>) = G_UZP2 [[COPY]], [[COPY1]]
+    ; CHECK-NEXT: $q0 = COPY [[UZP2_]](<4 x s32>)
+    ; CHECK-NEXT: RET_ReallyLR implicit $q0
     %0:_(<4 x s32>) = COPY $q0
     %1:_(<4 x s32>) = COPY $q1
-    %1:_(<4 x s32>) = G_SHUFFLE_VECTOR %0(<4 x s32>), %1, shufflemask(1, 3, -1, 7)
-    $q0 = COPY %1(<4 x s32>)
+    %2:_(<4 x s32>) = G_SHUFFLE_VECTOR %0(<4 x s32>), %1, shufflemask(1, 3, -1, 7)
+    $q0 = COPY %2(<4 x s32>)
     RET_ReallyLR implicit $q0