Index: include/llvm/IR/DataLayout.h
===================================================================
--- include/llvm/IR/DataLayout.h
+++ include/llvm/IR/DataLayout.h
@@ -475,7 +475,8 @@
 class StructLayout {
   uint64_t StructSize;
   unsigned StructAlignment;
-  unsigned NumElements;
+  bool IsPadded : 1;
+  unsigned NumElements : 31;
   uint64_t MemberOffsets[1]; // variable sized array!
 public:
   uint64_t getSizeInBytes() const { return StructSize; }
@@ -484,6 +485,10 @@
 
   unsigned getAlignment() const { return StructAlignment; }
 
+  /// Returns whether the struct has padding or not between its fields.
+  /// NB: Padding in nested element is not taken into account.
+  bool hasPadding() const { return IsPadded; }
+
   /// \brief Given a valid byte offset into the structure, returns the structure
   /// index that contains it.
   unsigned getElementContainingOffset(uint64_t Offset) const;
Index: lib/IR/DataLayout.cpp
===================================================================
--- lib/IR/DataLayout.cpp
+++ lib/IR/DataLayout.cpp
@@ -41,6 +41,7 @@
   assert(!ST->isOpaque() && "Cannot get layout of opaque structs");
   StructAlignment = 0;
   StructSize = 0;
+  IsPadded = false;
   NumElements = ST->getNumElements();
 
   // Loop over each of the elements, placing them in memory.
@@ -49,8 +50,10 @@
     unsigned TyAlign = ST->isPacked() ? 1 : DL.getABITypeAlignment(Ty);
 
     // Add padding if necessary to align the data element properly.
-    if ((StructSize & (TyAlign-1)) != 0)
+    if ((StructSize & (TyAlign-1)) != 0) {
+      IsPadded = true;
       StructSize = RoundUpToAlignment(StructSize, TyAlign);
+    }
 
     // Keep track of maximum alignment constraint.
     StructAlignment = std::max(TyAlign, StructAlignment);
@@ -64,8 +67,10 @@
 
   // Add padding to the end of the struct so that it could be put in an array
   // and all array elements would be aligned correctly.
-  if ((StructSize & (StructAlignment-1)) != 0)
+  if ((StructSize & (StructAlignment-1)) != 0) {
+    IsPadded = true;
     StructSize = RoundUpToAlignment(StructSize, StructAlignment);
+  }
 }
 
 
Index: lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -524,12 +524,40 @@
 
   if (auto *ST = dyn_cast<StructType>(T)) {
     // If the struct only have one element, we unpack.
-    if (ST->getNumElements() == 1) {
+    unsigned Count = ST->getNumElements();
+    if (Count == 1) {
       LoadInst *NewLoad = combineLoadToNewType(IC, LI, ST->getTypeAtIndex(0U),
                                                ".unpack");
       return IC.ReplaceInstUsesWith(LI, IC.Builder->CreateInsertValue(
         UndefValue::get(T), NewLoad, 0, LI.getName()));
     }
+
+    // We don't want to break loads with padding here as we'd loose
+    // the knowledge that padding exists for the rest of the pipeline.
+    const DataLayout &DL = IC.getDataLayout();
+    auto *SL = DL.getStructLayout(ST);
+    if (SL->hasPadding())
+      return nullptr;
+
+    auto Name = LI.getName();
+    auto LoadName = LI.getName() + ".unpack";
+    auto EltName = Name + ".elt";
+    auto *Addr = LI.getPointerOperand();
+    Value *V = UndefValue::get(T);
+    auto *IdxType = Type::getInt32Ty(ST->getContext());
+    auto *Zero = ConstantInt::get(IdxType, 0);
+    for (unsigned i = 0; i < Count; i++) {
+      Value *Indices[2] = {
+        Zero,
+        ConstantInt::get(IdxType, i),
+      };
+      auto *Ptr = IC.Builder->CreateInBoundsGEP(ST, Addr, makeArrayRef(Indices), EltName);
+      auto *L = IC.Builder->CreateLoad(ST->getTypeAtIndex(i), Ptr, LoadName);
+      V = IC.Builder->CreateInsertValue(V, L, i);
+    }
+
+    V->setName(Name);
+    return IC.ReplaceInstUsesWith(LI, V);
   }
 
   if (auto *AT = dyn_cast<ArrayType>(T)) {
@@ -902,11 +930,36 @@
 
   if (auto *ST = dyn_cast<StructType>(T)) {
     // If the struct only have one element, we unpack.
-    if (ST->getNumElements() == 1) {
+    unsigned Count = ST->getNumElements();
+    if (Count == 1) {
       V = IC.Builder->CreateExtractValue(V, 0);
       combineStoreToNewValue(IC, SI, V);
       return true;
     }
+
+    // We don't want to break loads with padding here as we'd loose
+    // the knowledge that padding exists for the rest of the pipeline.
+    const DataLayout &DL = IC.getDataLayout();
+    auto *SL = DL.getStructLayout(ST);
+    if (SL->hasPadding())
+      return false;
+
+    auto EltName = V->getName() + ".elt";
+    auto *Addr = SI.getPointerOperand();
+    auto AddrName = Addr->getName() + ".repack";
+    auto *IdxType = Type::getInt32Ty(ST->getContext());
+    auto *Zero = ConstantInt::get(IdxType, 0);
+    for (unsigned i = 0; i < Count; i++) {
+      Value *Indices[2] = {
+        Zero,
+        ConstantInt::get(IdxType, i),
+      };
+      auto *Ptr = IC.Builder->CreateInBoundsGEP(ST, Addr, makeArrayRef(Indices), AddrName);
+      auto *Val = IC.Builder->CreateExtractValue(V, i, EltName);
+      IC.Builder->CreateStore(Val, Ptr);
+    }
+
+    return true;
   }
 
   if (auto *AT = dyn_cast<ArrayType>(T)) {
Index: lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- lib/Transforms/InstCombine/InstructionCombining.cpp
+++ lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2311,9 +2311,10 @@
   }
   if (LoadInst *L = dyn_cast<LoadInst>(Agg))
     // If the (non-volatile) load only has one use, we can rewrite this to a
-    // load from a GEP. This reduces the size of the load.
-    // FIXME: If a load is used only by extractvalue instructions then this
-    //        could be done regardless of having multiple uses.
+    // load from a GEP. This reduces the size of the load. If a load is used
+    // only by extractvalue instructions then this either must have been
+    // optimized before, or it is a struct with padding, in which case we
+    // don't want to do the transformation as it loses padding knowledge.
     if (L->isSimple() && L->hasOneUse()) {
       // extractvalue has integer indices, getelementptr has Value*s. Convert.
       SmallVector<Value*, 4> Indices;
Index: test/Transforms/InstCombine/cast.ll
===================================================================
--- test/Transforms/InstCombine/cast.ll
+++ test/Transforms/InstCombine/cast.ll
@@ -722,7 +722,7 @@
 ; CHECK: ret i1 false
 }
 
-%s = type { i32, i32, i32 }
+%s = type { i32, i32, i16 }
 
 define %s @test68(%s *%p, i64 %i) {
 ; CHECK-LABEL: @test68(
Index: test/Transforms/InstCombine/extractvalue.ll
===================================================================
--- test/Transforms/InstCombine/extractvalue.ll
+++ test/Transforms/InstCombine/extractvalue.ll
@@ -48,16 +48,16 @@
 ; CHECK: call {{.*}}(i32 [[LOAD]])
 ; CHECK-NOT: extractvalue
 ; CHECK: ret i32 [[LOAD]]
-define i32 @extract2gep({i32, i32}* %pair, i32* %P) {
+define i32 @extract2gep({i16, i32}* %pair, i32* %P) {
         ; The load + extractvalue should be converted
         ; to an inbounds gep + smaller load.
         ; The new load should be in the same spot as the old load.
-        %L = load {i32, i32}, {i32, i32}* %pair
+        %L = load {i16, i32}, {i16, i32}* %pair
         store i32 0, i32* %P
         br label %loop
 
 loop:
-        %E = extractvalue {i32, i32} %L, 1
+        %E = extractvalue {i16, i32} %L, 1
         %C = call i32 @baz(i32 %E)
         store i32 %C, i32* %P
         %cond = icmp eq i32 %C, 0
@@ -67,17 +67,17 @@
         ret i32 %E
 }
 
-; CHECK-LABEL: define i32 @doubleextract2gep(
+; CHECK-LABEL: define i16 @doubleextract2gep(
 ; CHECK-NEXT: [[GEP:%[a-z0-9]+]] = getelementptr inbounds {{.*}}, {{.*}}* %arg, i64 0, i32 1, i32 1
-; CHECK-NEXT: [[LOAD:%[A-Za-z0-9]+]] = load i32, i32* [[GEP]]
-; CHECK-NEXT: ret i32 [[LOAD]]
-define i32 @doubleextract2gep({i32, {i32, i32}}* %arg) {
+; CHECK-NEXT: [[LOAD:%[A-Za-z0-9]+]] = load i16, i16* [[GEP]]
+; CHECK-NEXT: ret i16 [[LOAD]]
+define i16 @doubleextract2gep({i16, {i32, i16}}* %arg) {
         ; The load + extractvalues should be converted
         ; to a 3-index inbounds gep + smaller load.
-        %L = load {i32, {i32, i32}}, {i32, {i32, i32}}* %arg
-        %E1 = extractvalue {i32, {i32, i32}} %L, 1
-        %E2 = extractvalue {i32, i32} %E1, 1
-        ret i32 %E2
+        %L = load {i16, {i32, i16}}, {i16, {i32, i16}}* %arg
+        %E1 = extractvalue {i16, {i32, i16}} %L, 1
+        %E2 = extractvalue {i32, i16} %E1, 1
+        ret i16 %E2
 }
 
 ; CHECK: define i32 @nogep-multiuse
Index: test/Transforms/InstCombine/unpack-fca.ll
===================================================================
--- test/Transforms/InstCombine/unpack-fca.ll
+++ test/Transforms/InstCombine/unpack-fca.ll
@@ -5,110 +5,134 @@
 
 %A__vtbl = type { i8*, i32 (%A*)* }
 %A = type { %A__vtbl* }
+%B = type { i8*, i64 }
 
 @A__vtblZ = constant %A__vtbl { i8* null, i32 (%A*)* @A.foo }
 
 declare i32 @A.foo(%A* nocapture %this)
 
-declare i8* @allocmemory(i64)
-
-define void @storeA() {
-body:
-  %0 = tail call i8* @allocmemory(i64 32)
-  %1 = bitcast i8* %0 to %A*
+define void @storeA(%A* %a.ptr) {
 ; CHECK-LABEL: storeA
-; CHECK: store %A__vtbl* @A__vtblZ
-  store %A { %A__vtbl* @A__vtblZ }, %A* %1, align 8
+; CHECK-NEXT: [[GEP:%[a-z0-9\.]+]] = getelementptr inbounds %A, %A* %a.ptr, i64 0, i32 0
+; CHECK-NEXT: store %A__vtbl* @A__vtblZ, %A__vtbl** [[GEP]], align 8
+; CHECK-NEXT: ret void
+  store %A { %A__vtbl* @A__vtblZ }, %A* %a.ptr, align 8
+  ret void
+}
+
+define void @storeB(%B* %b.ptr) {
+; CHECK-LABEL: storeB
+; CHECK-NEXT: [[GEP1:%[a-z0-9\.]+]] = getelementptr inbounds %B, %B* %b.ptr, i64 0, i32 0
+; CHECK-NEXT: store i8* null, i8** [[GEP1]], align 8
+; CHECK-NEXT: [[GEP2:%[a-z0-9\.]+]] = getelementptr inbounds %B, %B* %b.ptr, i64 0, i32 1
+; CHECK-NEXT: store i64 42, i64* [[GEP2]], align 8
+; CHECK-NEXT: ret void
+  store %B { i8* null, i64 42 }, %B* %b.ptr, align 8
   ret void
 }
 
-define void @storeStructOfA() {
-body:
-  %0 = tail call i8* @allocmemory(i64 32)
-  %1 = bitcast i8* %0 to { %A }*
+define void @storeStructOfA({ %A }* %sa.ptr) {
 ; CHECK-LABEL: storeStructOfA
-; CHECK: store %A__vtbl* @A__vtblZ
-  store { %A } { %A { %A__vtbl* @A__vtblZ } }, { %A }* %1, align 8
+; CHECK-NEXT: [[GEP:%[a-z0-9\.]+]] = getelementptr inbounds { %A }, { %A }* %sa.ptr, i64 0, i32 0, i32 0
+; CHECK-NEXT: store %A__vtbl* @A__vtblZ, %A__vtbl** [[GEP]], align 8
+; CHECK-NEXT: ret void
+  store { %A } { %A { %A__vtbl* @A__vtblZ } }, { %A }* %sa.ptr, align 8
   ret void
 }
 
-define void @storeArrayOfA() {
-body:
-  %0 = tail call i8* @allocmemory(i64 32)
-  %1 = bitcast i8* %0 to [1 x %A]*
+define void @storeArrayOfA([1 x %A]* %aa.ptr) {
 ; CHECK-LABEL: storeArrayOfA
-; CHECK: store %A__vtbl* @A__vtblZ
-  store [1 x %A] [%A { %A__vtbl* @A__vtblZ }], [1 x %A]* %1, align 8
+; CHECK-NEXT: [[GEP:%[a-z0-9\.]+]] = getelementptr inbounds [1 x %A], [1 x %A]* %aa.ptr, i64 0, i64 0, i32 0
+; CHECK-NEXT: store %A__vtbl* @A__vtblZ, %A__vtbl** [[GEP]], align 8
+; CHECK-NEXT: ret void
+  store [1 x %A] [%A { %A__vtbl* @A__vtblZ }], [1 x %A]* %aa.ptr, align 8
   ret void
 }
 
-define void @storeStructOfArrayOfA() {
-body:
-  %0 = tail call i8* @allocmemory(i64 32)
-  %1 = bitcast i8* %0 to { [1 x %A] }*
+define void @storeStructOfArrayOfA({ [1 x %A] }* %saa.ptr) {
 ; CHECK-LABEL: storeStructOfArrayOfA
-; CHECK: store %A__vtbl* @A__vtblZ
-  store { [1 x %A] } { [1 x %A] [%A { %A__vtbl* @A__vtblZ }] }, { [1 x %A] }* %1, align 8
+; CHECK-NEXT: [[GEP:%[a-z0-9\.]+]] = getelementptr inbounds { [1 x %A] }, { [1 x %A] }* %saa.ptr, i64 0, i32 0, i64 0, i32 0
+; CHECK-NEXT: store %A__vtbl* @A__vtblZ, %A__vtbl** [[GEP]], align 8
+; CHECK-NEXT: ret void
+  store { [1 x %A] } { [1 x %A] [%A { %A__vtbl* @A__vtblZ }] }, { [1 x %A] }* %saa.ptr, align 8
   ret void
 }
 
-define %A @loadA() {
-body:
-  %0 = tail call i8* @allocmemory(i64 32)
-  %1 = bitcast i8* %0 to %A*
+define %A @loadA(%A* %a.ptr) {
 ; CHECK-LABEL: loadA
-; CHECK: load %A__vtbl*,
-; CHECK: insertvalue %A undef, %A__vtbl* {{.*}}, 0
-  %2 = load %A, %A* %1, align 8
-  ret %A %2
+; CHECK-NEXT: [[GEP:%[a-z0-9\.]+]] = getelementptr inbounds %A, %A* %a.ptr, i64 0, i32 0
+; CHECK-NEXT: [[LOAD:%[a-z0-9\.]+]] = load %A__vtbl*, %A__vtbl** [[GEP]], align 8
+; CHECK-NEXT: [[IV:%[a-z0-9\.]+]] = insertvalue %A undef, %A__vtbl* [[LOAD]], 0
+; CHECK-NEXT: ret %A [[IV]]
+  %1 = load %A, %A* %a.ptr, align 8
+  ret %A %1
 }
 
-define { %A } @loadStructOfA() {
-body:
-  %0 = tail call i8* @allocmemory(i64 32)
-  %1 = bitcast i8* %0 to { %A }*
+define %B @loadB(%B* %b.ptr) {
+; CHECK-LABEL: loadB
+; CHECK-NEXT: [[GEP1:%[a-z0-9\.]+]] = getelementptr inbounds %B, %B* %b.ptr, i64 0, i32 0
+; CHECK-NEXT: [[LOAD1:%[a-z0-9\.]+]] = load i8*, i8** [[GEP1]], align 8
+; CHECK-NEXT: [[IV1:%[a-z0-9\.]+]] = insertvalue %B undef, i8* [[LOAD1]], 0
+; CHECK-NEXT: [[GEP2:%[a-z0-9\.]+]] = getelementptr inbounds %B, %B* %b.ptr, i64 0, i32 1
+; CHECK-NEXT: [[LOAD2:%[a-z0-9\.]+]] = load i64, i64* [[GEP2]], align 8
+; CHECK-NEXT: [[IV2:%[a-z0-9\.]+]] = insertvalue %B [[IV1]], i64 [[LOAD2]], 1
+; CHECK-NEXT: ret %B [[IV2]]
+  %1 = load %B, %B* %b.ptr, align 8
+  ret %B %1
+}
+
+define { %A } @loadStructOfA({ %A }* %sa.ptr) {
 ; CHECK-LABEL: loadStructOfA
-; CHECK: load %A__vtbl*,
-; CHECK: insertvalue %A undef, %A__vtbl* {{.*}}, 0
-; CHECK: insertvalue { %A } undef, %A {{.*}}, 0
-  %2 = load { %A }, { %A }* %1, align 8
-  ret { %A } %2
+; CHECK-NEXT: [[GEP:%[a-z0-9\.]+]] = getelementptr inbounds { %A }, { %A }* %sa.ptr, i64 0, i32 0, i32 0
+; CHECK-NEXT: [[LOAD:%[a-z0-9\.]+]] = load %A__vtbl*, %A__vtbl** [[GEP]], align 8
+; CHECK-NEXT: [[IV1:%[a-z0-9\.]+]] = insertvalue %A undef, %A__vtbl* [[LOAD]], 0
+; CHECK-NEXT: [[IV2:%[a-z0-9\.]+]] = insertvalue { %A } undef, %A [[IV1]], 0
+; CHECK-NEXT: ret { %A } [[IV2]]
+  %1 = load { %A }, { %A }* %sa.ptr, align 8
+  ret { %A } %1
 }
 
-define [1 x %A] @loadArrayOfA() {
-body:
-  %0 = tail call i8* @allocmemory(i64 32)
-  %1 = bitcast i8* %0 to [1 x %A]*
+define [1 x %A] @loadArrayOfA([1 x %A]* %aa.ptr) {
 ; CHECK-LABEL: loadArrayOfA
-; CHECK: load %A__vtbl*,
-; CHECK: insertvalue %A undef, %A__vtbl* {{.*}}, 0
-; CHECK: insertvalue [1 x %A] undef, %A {{.*}}, 0
-  %2 = load [1 x %A], [1 x %A]* %1, align 8
-  ret [1 x %A] %2
+; CHECK-NEXT: [[GEP:%[a-z0-9\.]+]] = getelementptr inbounds [1 x %A], [1 x %A]* %aa.ptr, i64 0, i64 0, i32 0
+; CHECK-NEXT: [[LOAD:%[a-z0-9\.]+]] = load %A__vtbl*, %A__vtbl** [[GEP]], align 8
+; CHECK-NEXT: [[IV1:%[a-z0-9\.]+]] = insertvalue %A undef, %A__vtbl* [[LOAD]], 0
+; CHECK-NEXT: [[IV2:%[a-z0-9\.]+]] = insertvalue [1 x %A] undef, %A [[IV1]], 0
+; CHECK-NEXT: ret [1 x %A] [[IV2]]
+  %1 = load [1 x %A], [1 x %A]* %aa.ptr, align 8
+  ret [1 x %A] %1
 }
 
-define { [1 x %A] } @loadStructOfArrayOfA() {
-body:
-  %0 = tail call i8* @allocmemory(i64 32)
-  %1 = bitcast i8* %0 to { [1 x %A] }*
+define { [1 x %A] } @loadStructOfArrayOfA({ [1 x %A] }* %saa.ptr) {
 ; CHECK-LABEL: loadStructOfArrayOfA
-; CHECK: load %A__vtbl*,
-; CHECK: insertvalue %A undef, %A__vtbl* {{.*}}, 0
-; CHECK: insertvalue [1 x %A] undef, %A {{.*}}, 0
-; CHECK: insertvalue { [1 x %A] } undef, [1 x %A] {{.*}}, 0
-  %2 = load { [1 x %A] }, { [1 x %A] }* %1, align 8
-  ret { [1 x %A] } %2
+; CHECK-NEXT: [[GEP:%[a-z0-9\.]+]] = getelementptr inbounds { [1 x %A] }, { [1 x %A] }* %saa.ptr, i64 0, i32 0, i64 0, i32 0
+; CHECK-NEXT: [[LOAD:%[a-z0-9\.]+]] = load %A__vtbl*, %A__vtbl** [[GEP]], align 8
+; CHECK-NEXT: [[IV1:%[a-z0-9\.]+]] = insertvalue %A undef, %A__vtbl* [[LOAD]], 0
+; CHECK-NEXT: [[IV2:%[a-z0-9\.]+]] = insertvalue [1 x %A] undef, %A [[IV1]], 0
+; CHECK-NEXT: [[IV3:%[a-z0-9\.]+]] = insertvalue { [1 x %A] } undef, [1 x %A] [[IV2]], 0
+; CHECK-NEXT: ret { [1 x %A] } [[IV3]]
+  %1 = load { [1 x %A] }, { [1 x %A] }* %saa.ptr, align 8
+  ret { [1 x %A] } %1
 }
 
-define { %A } @structOfA() {
-body:
-  %0 = tail call i8* @allocmemory(i64 32)
-  %1 = bitcast i8* %0 to { %A }*
+define { %A } @structOfA({ %A }* %sa.ptr) {
 ; CHECK-LABEL: structOfA
-; CHECK: store %A__vtbl* @A__vtblZ
-  store { %A } { %A { %A__vtbl* @A__vtblZ } }, { %A }* %1, align 8
-  %2 = load { %A }, { %A }* %1, align 8
-; CHECK-NOT: load
-; CHECK: ret { %A } { %A { %A__vtbl* @A__vtblZ } }
-  ret { %A } %2
+; CHECK-NEXT: [[GEP:%[a-z0-9\.]+]] = getelementptr inbounds { %A }, { %A }* %sa.ptr, i64 0, i32 0, i32 0
+; CHECK-NEXT: store %A__vtbl* @A__vtblZ, %A__vtbl** [[GEP]], align 8
+; CHECK-NEXT: ret { %A } { %A { %A__vtbl* @A__vtblZ } }
+  store { %A } { %A { %A__vtbl* @A__vtblZ } }, { %A }* %sa.ptr, align 8
+  %1 = load { %A }, { %A }* %sa.ptr, align 8
+  ret { %A } %1
+}
+
+define %B @structB(%B* %b.ptr) {
+; CHECK-LABEL: structB
+; CHECK-NEXT: [[GEP1:%[a-z0-9\.]+]] = getelementptr inbounds %B, %B* %b.ptr, i64 0, i32 0
+; CHECK-NEXT: store i8* null, i8** [[GEP1]], align 8
+; CHECK-NEXT: [[GEP2:%[a-z0-9\.]+]] = getelementptr inbounds %B, %B* %b.ptr, i64 0, i32 1
+; CHECK-NEXT: store i64 42, i64* [[GEP2]], align 8
+; CHECK-NEXT: ret %B { i8* null, i64 42 }
+  store %B { i8* null, i64 42 }, %B* %b.ptr, align 8
+  %1 = load %B, %B* %b.ptr, align 8
+  ret %B %1
 }