diff --git a/llvm/lib/Target/AMDGPU/AMDGPUPromoteAlloca.cpp b/llvm/lib/Target/AMDGPU/AMDGPUPromoteAlloca.cpp
--- a/llvm/lib/Target/AMDGPU/AMDGPUPromoteAlloca.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUPromoteAlloca.cpp
@@ -386,6 +386,8 @@
   };
 
   Type *VecEltTy = VectorTy->getElementType();
+  const unsigned NumVecElts = VectorTy->getNumElements();
+
   switch (Inst->getOpcode()) {
   case Instruction::Load: {
     // Loads can only be lowered if the value is known.
@@ -413,13 +415,13 @@
     // Loading a subvector.
     if (isa<FixedVectorType>(AccessTy)) {
       assert(AccessSize.isKnownMultipleOf(DL.getTypeStoreSize(VecEltTy)));
-      const unsigned NumElts = AccessSize / DL.getTypeStoreSize(VecEltTy);
-      auto *SubVecTy = FixedVectorType::get(VecEltTy, NumElts);
+      const unsigned NumLoadedElts = AccessSize / DL.getTypeStoreSize(VecEltTy);
+      auto *SubVecTy = FixedVectorType::get(VecEltTy, NumLoadedElts);
       assert(DL.getTypeStoreSize(SubVecTy) == DL.getTypeStoreSize(AccessTy));
 
       unsigned IndexVal = cast<ConstantInt>(Index)->getZExtValue();
       Value *SubVec = PoisonValue::get(SubVecTy);
-      for (unsigned K = 0; K < NumElts; ++K) {
+      for (unsigned K = 0; K < NumLoadedElts; ++K) {
         SubVec = Builder.CreateInsertElement(
             SubVec, Builder.CreateExtractElement(CurVal, IndexVal + K), K);
       }
@@ -465,8 +467,9 @@
     // Storing a subvector.
     if (isa<FixedVectorType>(AccessTy)) {
       assert(AccessSize.isKnownMultipleOf(DL.getTypeStoreSize(VecEltTy)));
-      const unsigned NumElts = AccessSize / DL.getTypeStoreSize(VecEltTy);
-      auto *SubVecTy = FixedVectorType::get(VecEltTy, NumElts);
+      const unsigned NumWrittenElts =
+          AccessSize / DL.getTypeStoreSize(VecEltTy);
+      auto *SubVecTy = FixedVectorType::get(VecEltTy, NumWrittenElts);
       assert(DL.getTypeStoreSize(SubVecTy) == DL.getTypeStoreSize(AccessTy));
 
       if (SubVecTy->isPtrOrPtrVectorTy())
@@ -478,7 +481,8 @@
 
       unsigned IndexVal = cast<ConstantInt>(Index)->getZExtValue();
       Value *CurVec = GetOrLoadCurrentVectorValue();
-      for (unsigned K = 0; (IndexVal + K) < NumElts; ++K) {
+      for (unsigned K = 0; K < NumWrittenElts && ((IndexVal + K) < NumVecElts);
+           ++K) {
         CurVec = Builder.CreateInsertElement(
             CurVec, Builder.CreateExtractElement(Val, K), IndexVal + K);
       }
diff --git a/llvm/test/CodeGen/AMDGPU/promote-alloca-subvecs.ll b/llvm/test/CodeGen/AMDGPU/promote-alloca-subvecs.ll
--- a/llvm/test/CodeGen/AMDGPU/promote-alloca-subvecs.ll
+++ b/llvm/test/CodeGen/AMDGPU/promote-alloca-subvecs.ll
@@ -13,13 +13,21 @@
 ; CHECK-NEXT:    [[TMP3:%.*]] = insertelement <4 x i64> [[TMP1]], i64 [[TMP2]], i64 1
 ; CHECK-NEXT:    [[TMP4:%.*]] = extractelement <2 x i64> [[VAL_1]], i64 0
 ; CHECK-NEXT:    [[TMP5:%.*]] = insertelement <4 x i64> [[TMP3]], i64 [[TMP4]], i64 1
-; CHECK-NEXT:    [[TMP6:%.*]] = insertelement <2 x i64> poison, i64 [[TMP0]], i64 0
-; CHECK-NEXT:    [[TMP7:%.*]] = insertelement <2 x i64> [[TMP6]], i64 [[TMP4]], i64 1
-; CHECK-NEXT:    [[DUMMYUSER:%.*]] = freeze <2 x i64> [[TMP7]]
-; CHECK-NEXT:    [[TMP8:%.*]] = insertelement <2 x i64> poison, i64 [[TMP4]], i64 0
-; CHECK-NEXT:    [[TMP9:%.*]] = insertelement <2 x i64> [[TMP8]], i64 undef, i64 1
-; CHECK-NEXT:    [[DUMMYUSER_1:%.*]] = freeze <2 x i64> [[TMP9]]
-; CHECK-NEXT:    [[DUMMYUSER_2:%.*]] = freeze <2 x i64> undef
+; CHECK-NEXT:    [[TMP6:%.*]] = extractelement <2 x i64> [[VAL_1]], i64 1
+; CHECK-NEXT:    [[TMP7:%.*]] = insertelement <4 x i64> [[TMP5]], i64 [[TMP6]], i64 2
+; CHECK-NEXT:    [[TMP8:%.*]] = extractelement <2 x i64> [[VAL_1]], i64 0
+; CHECK-NEXT:    [[TMP9:%.*]] = insertelement <4 x i64> [[TMP7]], i64 [[TMP8]], i64 2
+; CHECK-NEXT:    [[TMP10:%.*]] = extractelement <2 x i64> [[VAL_1]], i64 1
+; CHECK-NEXT:    [[TMP11:%.*]] = insertelement <4 x i64> [[TMP9]], i64 [[TMP10]], i64 3
+; CHECK-NEXT:    [[TMP12:%.*]] = insertelement <2 x i64> poison, i64 [[TMP0]], i64 0
+; CHECK-NEXT:    [[TMP13:%.*]] = insertelement <2 x i64> [[TMP12]], i64 [[TMP4]], i64 1
+; CHECK-NEXT:    [[DUMMYUSER:%.*]] = freeze <2 x i64> [[TMP13]]
+; CHECK-NEXT:    [[TMP14:%.*]] = insertelement <2 x i64> poison, i64 [[TMP4]], i64 0
+; CHECK-NEXT:    [[TMP15:%.*]] = insertelement <2 x i64> [[TMP14]], i64 [[TMP8]], i64 1
+; CHECK-NEXT:    [[DUMMYUSER_1:%.*]] = freeze <2 x i64> [[TMP15]]
+; CHECK-NEXT:    [[TMP16:%.*]] = insertelement <2 x i64> poison, i64 [[TMP8]], i64 0
+; CHECK-NEXT:    [[TMP17:%.*]] = insertelement <2 x i64> [[TMP16]], i64 [[TMP10]], i64 1
+; CHECK-NEXT:    [[DUMMYUSER_2:%.*]] = freeze <2 x i64> [[TMP17]]
 ; CHECK-NEXT:    ret void
 ;
 entry:
@@ -58,17 +66,30 @@
 ; CHECK-NEXT:    [[TMP8:%.*]] = bitcast <8 x i16> [[VAL_1]] to <2 x i64>
 ; CHECK-NEXT:    [[TMP9:%.*]] = extractelement <2 x i64> [[TMP8]], i64 0
 ; CHECK-NEXT:    [[TMP10:%.*]] = insertelement <4 x i64> [[TMP4]], i64 [[TMP9]], i64 1
-; CHECK-NEXT:    [[TMP11:%.*]] = insertelement <2 x i64> poison, i64 [[TMP9]], i64 0
-; CHECK-NEXT:    [[TMP12:%.*]] = insertelement <2 x i64> [[TMP11]], i64 undef, i64 1
-; CHECK-NEXT:    [[TMP13:%.*]] = bitcast <2 x i64> [[TMP12]] to <8 x i16>
-; CHECK-NEXT:    [[DUMMYUSE_1:%.*]] = freeze <8 x i16> [[TMP13]]
-; CHECK-NEXT:    [[TMP14:%.*]] = bitcast <16 x i8> [[VAL_2]] to <2 x i64>
-; CHECK-NEXT:    [[DUMMYUSE_2:%.*]] = freeze <4 x i32> undef
-; CHECK-NEXT:    [[TMP15:%.*]] = bitcast <128 x i1> [[VAL_3]] to <2 x i64>
-; CHECK-NEXT:    [[TMP16:%.*]] = insertelement <2 x i64> poison, i64 [[TMP9]], i64 0
-; CHECK-NEXT:    [[TMP17:%.*]] = insertelement <2 x i64> [[TMP16]], i64 undef, i64 1
-; CHECK-NEXT:    [[TMP18:%.*]] = bitcast <2 x i64> [[TMP17]] to <128 x i1>
-; CHECK-NEXT:    [[DUMMYUSE_I1:%.*]] = freeze <128 x i1> [[TMP18]]
+; CHECK-NEXT:    [[TMP11:%.*]] = extractelement <2 x i64> [[TMP8]], i64 1
+; CHECK-NEXT:    [[TMP12:%.*]] = insertelement <4 x i64> [[TMP10]], i64 [[TMP11]], i64 2
+; CHECK-NEXT:    [[TMP13:%.*]] = insertelement <2 x i64> poison, i64 [[TMP9]], i64 0
+; CHECK-NEXT:    [[TMP14:%.*]] = insertelement <2 x i64> [[TMP13]], i64 [[TMP11]], i64 1
+; CHECK-NEXT:    [[TMP15:%.*]] = bitcast <2 x i64> [[TMP14]] to <8 x i16>
+; CHECK-NEXT:    [[DUMMYUSE_1:%.*]] = freeze <8 x i16> [[TMP15]]
+; CHECK-NEXT:    [[TMP16:%.*]] = bitcast <16 x i8> [[VAL_2]] to <2 x i64>
+; CHECK-NEXT:    [[TMP17:%.*]] = extractelement <2 x i64> [[TMP16]], i64 0
+; CHECK-NEXT:    [[TMP18:%.*]] = insertelement <4 x i64> [[TMP12]], i64 [[TMP17]], i64 2
+; CHECK-NEXT:    [[TMP19:%.*]] = extractelement <2 x i64> [[TMP16]], i64 1
+; CHECK-NEXT:    [[TMP20:%.*]] = insertelement <4 x i64> [[TMP18]], i64 [[TMP19]], i64 3
+; CHECK-NEXT:    [[TMP21:%.*]] = insertelement <2 x i64> poison, i64 [[TMP17]], i64 0
+; CHECK-NEXT:    [[TMP22:%.*]] = insertelement <2 x i64> [[TMP21]], i64 [[TMP19]], i64 1
+; CHECK-NEXT:    [[TMP23:%.*]] = bitcast <2 x i64> [[TMP22]] to <4 x i32>
+; CHECK-NEXT:    [[DUMMYUSE_2:%.*]] = freeze <4 x i32> [[TMP23]]
+; CHECK-NEXT:    [[TMP24:%.*]] = bitcast <128 x i1> [[VAL_3]] to <2 x i64>
+; CHECK-NEXT:    [[TMP25:%.*]] = extractelement <2 x i64> [[TMP24]], i64 0
+; CHECK-NEXT:    [[TMP26:%.*]] = insertelement <4 x i64> [[TMP20]], i64 [[TMP25]], i64 2
+; CHECK-NEXT:    [[TMP27:%.*]] = extractelement <2 x i64> [[TMP24]], i64 1
+; CHECK-NEXT:    [[TMP28:%.*]] = insertelement <4 x i64> [[TMP26]], i64 [[TMP27]], i64 3
+; CHECK-NEXT:    [[TMP29:%.*]] = insertelement <2 x i64> poison, i64 [[TMP9]], i64 0
+; CHECK-NEXT:    [[TMP30:%.*]] = insertelement <2 x i64> [[TMP29]], i64 [[TMP25]], i64 1
+; CHECK-NEXT:    [[TMP31:%.*]] = bitcast <2 x i64> [[TMP30]] to <128 x i1>
+; CHECK-NEXT:    [[DUMMYUSE_I1:%.*]] = freeze <128 x i1> [[TMP31]]
 ; CHECK-NEXT:    ret void
 ;
 entry:
@@ -310,6 +331,8 @@
 ; CHECK-LABEL: define void @test_out_of_bounds_subvec
 ; CHECK-SAME: (<2 x i64> [[VAL:%.*]]) {
 ; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = extractelement <2 x i64> [[VAL]], i64 0
+; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <4 x i64> undef, i64 [[TMP0]], i64 3
 ; CHECK-NEXT:    ret void
 ;
 entry:
@@ -351,9 +374,9 @@
 ; CHECK-LABEL: define void @store_2xi32_into_double
 ; CHECK-SAME: (double [[FOO:%.*]]) {
 ; CHECK-NEXT:    [[DUMMYUSER0:%.*]] = freeze double 0x5F0000005E
-; CHECK-NEXT:    [[DUMMYUSER1:%.*]] = freeze double undef
-; CHECK-NEXT:    [[DUMMYUSER2:%.*]] = freeze double undef
-; CHECK-NEXT:    [[DUMMYUSER3:%.*]] = freeze double undef
+; CHECK-NEXT:    [[DUMMYUSER1:%.*]] = freeze double 0x6700000066
+; CHECK-NEXT:    [[DUMMYUSER2:%.*]] = freeze double 0x6900000068
+; CHECK-NEXT:    [[DUMMYUSER3:%.*]] = freeze double 0x6F0000006E
 ; CHECK-NEXT:    ret void
 ;
   %alloca = alloca [9 x double], align 8, addrspace(5)