Instcombine: destructor loads of structs that do not contains padding

For non padded structs, we can just proceed and deaggregate them.
We don't want ot do this when there is padding in the struct as to not
lose information about this padding (the subsequents passes would then
try hard to preserve the padding, which is undesirable).

Also update extractvalue.ll and cast.ll so that they use structs with padding.

Remove the FIXME in the extractvalue of laod case as the non padded case is
handled when processing the load, and we don't want to do it on the padded
case.

Patch by: Amaury SECHET <deadalnix@gmail.com>

Differential Revision: http://reviews.llvm.org/D14483

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 255600

llvm/include/llvm/IR/DataLayout.h

@@ -475,7 +475,8 @@ inline LLVMTargetDataRef wrap(const DataLayout *P) {
 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 @@ class StructLayout {
 
   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;

llvm/lib/IR/DataLayout.cpp

@@ -41,6 +41,7 @@ StructLayout::StructLayout(StructType *ST, const DataLayout &DL) {
   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 @@ StructLayout::StructLayout(StructType *ST, const DataLayout &DL) {
     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 @@ StructLayout::StructLayout(StructType *ST, const DataLayout &DL) {
 
   // 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);
+  }
 }
 
 

llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp

@@ -524,12 +524,40 @@ static Instruction *unpackLoadToAggregate(InstCombiner &IC, LoadInst &LI) {
 
   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 @@ static bool unpackStoreToAggregate(InstCombiner &IC, StoreInst &SI) {
 
   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)) {

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -2311,9 +2311,10 @@ Instruction *InstCombiner::visitExtractValueInst(ExtractValueInst &EV) {
   }
   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;

llvm/test/Transforms/InstCombine/cast.ll

@@ -722,7 +722,7 @@ define i1 @test67(i1 %a, i32 %b) {
 ; CHECK: ret i1 false
 }
 
-%s = type { i32, i32, i32 }
+%s = type { i32, i32, i16 }
 
 define %s @test68(%s *%p, i64 %i) {
 ; CHECK-LABEL: @test68(

llvm/test/Transforms/InstCombine/extractvalue.ll

@@ -48,16 +48,16 @@ define i32 @foo(i32 %a, i32 %b) {
 ; 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 @@ end:
         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