return visitAllocSite(AI);
}
+/// \brief Combine loads to match the type of value their uses after looking
+/// through intervening bitcasts.
+///
+/// The core idea here is that if the result of a load is used in an operation,
+/// we should load the type most conducive to that operation. For example, when
+/// loading an integer and converting that immediately to a pointer, we should
+/// instead directly load a pointer.
+///
+/// However, this routine must never change the width of a load or the number of
+/// loads as that would introduce a semantic change. This combine is expected to
+/// be a semantic no-op which just allows loads to more closely model the types
+/// of their consuming operations.
+///
+/// Currently, we also refuse to change the precise type used for an atomic load
+/// or a volatile load. This is debatable, and might be reasonable to change
+/// later. However, it is risky in case some backend or other part of LLVM is
+/// relying on the exact type loaded to select appropriate atomic operations.
+static Instruction *combineLoadToOperationType(InstCombiner &IC, LoadInst &LI) {
+ // FIXME: We could probably with some care handle both volatile and atomic
+ // loads here but it isn't clear that this is important.
+ if (!LI.isSimple())
+ return nullptr;
-/// InstCombineLoadCast - Fold 'load (cast P)' -> cast (load P)' when possible.
-static Instruction *InstCombineLoadCast(InstCombiner &IC, LoadInst &LI,
- const DataLayout *DL) {
- User *CI = cast<User>(LI.getOperand(0));
- Value *CastOp = CI->getOperand(0);
-
- PointerType *DestTy = cast<PointerType>(CI->getType());
- Type *DestPTy = DestTy->getElementType();
- if (PointerType *SrcTy = dyn_cast<PointerType>(CastOp->getType())) {
-
- // If the address spaces don't match, don't eliminate the cast.
- if (DestTy->getAddressSpace() != SrcTy->getAddressSpace())
- return nullptr;
-
- Type *SrcPTy = SrcTy->getElementType();
-
- if (DestPTy->isIntegerTy() || DestPTy->isPointerTy() ||
- DestPTy->isVectorTy()) {
- // If the source is an array, the code below will not succeed. Check to
- // see if a trivial 'gep P, 0, 0' will help matters. Only do this for
- // constants.
- if (ArrayType *ASrcTy = dyn_cast<ArrayType>(SrcPTy))
- if (Constant *CSrc = dyn_cast<Constant>(CastOp))
- if (ASrcTy->getNumElements() != 0) {
- Type *IdxTy = DL
- ? DL->getIntPtrType(SrcTy)
- : Type::getInt64Ty(SrcTy->getContext());
- Value *Idx = Constant::getNullValue(IdxTy);
- Value *Idxs[2] = { Idx, Idx };
- CastOp = ConstantExpr::getGetElementPtr(CSrc, Idxs);
- SrcTy = cast<PointerType>(CastOp->getType());
- SrcPTy = SrcTy->getElementType();
- }
-
- if (IC.getDataLayout() &&
- (SrcPTy->isIntegerTy() || SrcPTy->isPointerTy() ||
- SrcPTy->isVectorTy()) &&
- // Do not allow turning this into a load of an integer, which is then
- // casted to a pointer, this pessimizes pointer analysis a lot.
- (SrcPTy->isPtrOrPtrVectorTy() ==
- LI.getType()->isPtrOrPtrVectorTy()) &&
- IC.getDataLayout()->getTypeSizeInBits(SrcPTy) ==
- IC.getDataLayout()->getTypeSizeInBits(DestPTy)) {
-
- // Okay, we are casting from one integer or pointer type to another of
- // the same size. Instead of casting the pointer before the load, cast
- // the result of the loaded value.
- LoadInst *NewLoad =
- IC.Builder->CreateLoad(CastOp, LI.isVolatile(), CI->getName());
- NewLoad->setAlignment(LI.getAlignment());
- NewLoad->setAtomic(LI.getOrdering(), LI.getSynchScope());
- // Now cast the result of the load.
- PointerType *OldTy = dyn_cast<PointerType>(NewLoad->getType());
- PointerType *NewTy = dyn_cast<PointerType>(LI.getType());
- if (OldTy && NewTy &&
- OldTy->getAddressSpace() != NewTy->getAddressSpace()) {
- return new AddrSpaceCastInst(NewLoad, LI.getType());
- }
+ if (LI.use_empty())
+ return nullptr;
- return new BitCastInst(NewLoad, LI.getType());
- }
+ Value *Ptr = LI.getPointerOperand();
+ unsigned AS = LI.getPointerAddressSpace();
+
+ // Fold away bit casts of the loaded value by loading the desired type.
+ if (LI.hasOneUse())
+ if (auto *BC = dyn_cast<BitCastInst>(LI.user_back())) {
+ LoadInst *NewLoad = IC.Builder->CreateAlignedLoad(
+ IC.Builder->CreateBitCast(Ptr, BC->getDestTy()->getPointerTo(AS)),
+ LI.getAlignment(), LI.getName());
+ BC->replaceAllUsesWith(NewLoad);
+ IC.EraseInstFromFunction(*BC);
+ return &LI;
}
- }
+
+ // FIXME: We should also canonicalize loads of vectors when their elements are
+ // cast to other types.
return nullptr;
}
Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
Value *Op = LI.getOperand(0);
+ // Try to canonicalize the loaded type.
+ if (Instruction *Res = combineLoadToOperationType(*this, LI))
+ return Res;
+
// Attempt to improve the alignment.
if (DL) {
unsigned KnownAlign =
LI.setAlignment(EffectiveLoadAlign);
}
- // load (cast X) --> cast (load X) iff safe.
- if (isa<CastInst>(Op))
- if (Instruction *Res = InstCombineLoadCast(*this, LI, DL))
- return Res;
-
// None of the following transforms are legal for volatile/atomic loads.
// FIXME: Some of it is okay for atomic loads; needs refactoring.
if (!LI.isSimple()) return nullptr;
return ReplaceInstUsesWith(LI, UndefValue::get(LI.getType()));
}
- // Instcombine load (constantexpr_cast global) -> cast (load global)
- if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Op))
- if (CE->isCast())
- if (Instruction *Res = InstCombineLoadCast(*this, LI, DL))
- return Res;
-
if (Op->hasOneUse()) {
// Change select and PHI nodes to select values instead of addresses: this
// helps alias analysis out a lot, allows many others simplifications, and
define void @bitcast_alias_scalar(float* noalias %source, float* noalias %dest) nounwind {
entry:
; CHECK-LABEL: @bitcast_alias_scalar
-; CHECK: bitcast float %tmp to i32
+; CHECK: bitcast float* %source to i32*
+; CHECK: load i32*
; CHECK-NOT: fptoui
; CHECK-NOT: uitofp
; CHECK: bitcast i32 %call to float
define void @bitcast_alias_vector(<2 x float>* noalias %source, <2 x float>* noalias %dest) nounwind {
entry:
; CHECK-LABEL: @bitcast_alias_vector
-; CHECK: bitcast <2 x float> %tmp to <2 x i32>
+; CHECK: bitcast <2 x float>* %source to <2 x i32>*
+; CHECK: load <2 x i32>*
; CHECK-NOT: fptoui
; CHECK-NOT: uitofp
; CHECK: bitcast <2 x i32> %call to <2 x float>
define void @bitcast_alias_vector_scalar_same_size(<2 x float>* noalias %source, <2 x float>* noalias %dest) nounwind {
entry:
; CHECK-LABEL: @bitcast_alias_vector_scalar_same_size
-; CHECK: bitcast <2 x float> %tmp to i64
+; CHECK: bitcast <2 x float>* %source to i64*
+; CHECK: load i64*
; CHECK: %call = call i64 @func_i64
; CHECK: bitcast i64 %call to <2 x float>
%tmp = load <2 x float>* %source, align 8
define void @bitcast_alias_scalar_vector_same_size(i64* noalias %source, i64* noalias %dest) nounwind {
entry:
; CHECK-LABEL: @bitcast_alias_scalar_vector_same_size
-; CHECK: bitcast i64 %tmp to <2 x float>
+; CHECK: bitcast i64* %source to <2 x float>*
+; CHECK: load <2 x float>*
; CHECK: call <2 x float> @func_v2f32
; CHECK: bitcast <2 x float> %call to i64
%tmp = load i64* %source, align 8
define void @bitcast_alias_vector_ptrs_same_size(<2 x i64*>* noalias %source, <2 x i64*>* noalias %dest) nounwind {
entry:
; CHECK-LABEL: @bitcast_alias_vector_ptrs_same_size
-; CHECK: bitcast <2 x i64*> %tmp to <2 x i32*>
+; CHECK: bitcast <2 x i64*>* %source to <2 x i32*>*
+; CHECK: load <2 x i32*>*
; CHECK: call <2 x i32*> @func_v2i32p
; CHECK: bitcast <2 x i32*> %call to <2 x i64*>
%tmp = load <2 x i64*>* %source, align 8
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