[llvm] d9f5d7b - [InstCombine] Extract bitcast -> gep transform
Nikita Popov via llvm-commits
llvm-commits at lists.llvm.org
Wed Jun 23 13:44:43 PDT 2021
On Wed, Jun 23, 2021 at 10:18 PM David Blaikie <dblaikie at gmail.com> wrote:
> On Mon, Jun 21, 2021 at 12:25 PM Nikita Popov via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
> >
> >
> > Author: Nikita Popov
> > Date: 2021-06-21T21:24:50+02:00
> > New Revision: d9f5d7b959de36085944d4a99a73f3053f953796
> >
> > URL:
> https://github.com/llvm/llvm-project/commit/d9f5d7b959de36085944d4a99a73f3053f953796
> > DIFF:
> https://github.com/llvm/llvm-project/commit/d9f5d7b959de36085944d4a99a73f3053f953796.diff
> >
> > LOG: [InstCombine] Extract bitcast -> gep transform
> >
> > Move this into a separate function, to make sure that early
> > returns do not accidentally skip other transforms. There is
> > already one isSized() check that could run into this issue,
> > thus this change is not strictly NFC.
>
> Can/should this be tested, then?
>
Yeah :) I ended up reverting this and reapplying with a test in
https://github.com/llvm/llvm-project/commit/e2c2124a4b5bad9cf2a1e23a6aef1b2ad753f504
.
Nikita
> >
> > Added:
> >
> >
> > Modified:
> > llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
> >
> > Removed:
> >
> >
> >
> >
> ################################################################################
> > diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
> b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
> > index 9b38eb6ab24d..dcfff4552f11 100644
> > --- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
> > +++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
> > @@ -2603,6 +2603,52 @@ Instruction
> *InstCombinerImpl::optimizeBitCastFromPhi(CastInst &CI,
> > return RetVal;
> > }
> >
> > +static Instruction *convertBitCastToGEP(BitCastInst &CI, IRBuilderBase
> &Builder,
> > + const DataLayout &DL) {
> > + Value *Src = CI.getOperand(0);
> > + PointerType *SrcPTy = cast<PointerType>(Src->getType());
> > + PointerType *DstPTy = cast<PointerType>(CI.getType());
> > + Type *DstElTy = DstPTy->getElementType();
> > + Type *SrcElTy = SrcPTy->getElementType();
> > +
> > + // When the type pointed to is not sized the cast cannot be
> > + // turned into a gep.
> > + if (!SrcElTy->isSized())
> > + return nullptr;
> > +
> > + // If the source and destination are pointers, and this cast is
> equivalent
> > + // to a getelementptr X, 0, 0, 0... turn it into the appropriate gep.
> > + // This can enhance SROA and other transforms that want type-safe
> pointers.
> > + unsigned NumZeros = 0;
> > + while (SrcElTy && SrcElTy != DstElTy) {
> > + SrcElTy = GetElementPtrInst::getTypeAtIndex(SrcElTy, (uint64_t)0);
> > + ++NumZeros;
> > + }
> > +
> > + // If we found a path from the src to dest, create the getelementptr
> now.
> > + if (SrcElTy == DstElTy) {
> > + SmallVector<Value *, 8> Idxs(NumZeros + 1, Builder.getInt32(0));
> > + GetElementPtrInst *GEP =
> > + GetElementPtrInst::Create(SrcPTy->getElementType(), Src, Idxs);
> > +
> > + // If the source pointer is dereferenceable, then assume it points
> to an
> > + // allocated object and apply "inbounds" to the GEP.
> > + bool CanBeNull, CanBeFreed;
> > + if (Src->getPointerDereferenceableBytes(DL, CanBeNull, CanBeFreed))
> {
> > + // In a non-default address space (not 0), a null pointer can not
> be
> > + // assumed inbounds, so ignore that case
> (dereferenceable_or_null).
> > + // The reason is that 'null' is not treated
> > diff erently in these address
> > + // spaces, and we consequently ignore the 'gep inbounds' special
> case
> > + // for 'null' which allows 'inbounds' on 'null' if the indices are
> > + // zeros.
> > + if (SrcPTy->getAddressSpace() == 0 || !CanBeNull)
> > + GEP->setIsInBounds();
> > + }
> > + return GEP;
> > + }
> > + return nullptr;
> > +}
> > +
> > Instruction *InstCombinerImpl::visitBitCast(BitCastInst &CI) {
> > // If the operands are integer typed then apply the integer
> transforms,
> > // otherwise just apply the common ones.
> > @@ -2616,11 +2662,6 @@ Instruction
> *InstCombinerImpl::visitBitCast(BitCastInst &CI) {
> > return replaceInstUsesWith(CI, Src);
> >
> > if (isa<PointerType>(SrcTy) && isa<PointerType>(DestTy)) {
> > - PointerType *SrcPTy = cast<PointerType>(SrcTy);
> > - PointerType *DstPTy = cast<PointerType>(DestTy);
> > - Type *DstElTy = DstPTy->getElementType();
> > - Type *SrcElTy = SrcPTy->getElementType();
> > -
> > // If we are casting a alloca to a pointer to a type of the same
> > // size, rewrite the allocation instruction to allocate the "right"
> type.
> > // There is no need to modify malloc calls because it is their
> bitcast that
> > @@ -2629,43 +2670,8 @@ Instruction
> *InstCombinerImpl::visitBitCast(BitCastInst &CI) {
> > if (Instruction *V = PromoteCastOfAllocation(CI, *AI))
> > return V;
> >
> > - // When the type pointed to is not sized the cast cannot be
> > - // turned into a gep.
> > - Type *PointeeType =
> > -
> cast<PointerType>(Src->getType()->getScalarType())->getElementType();
> > - if (!PointeeType->isSized())
> > - return nullptr;
> > -
> > - // If the source and destination are pointers, and this cast is
> equivalent
> > - // to a getelementptr X, 0, 0, 0... turn it into the appropriate
> gep.
> > - // This can enhance SROA and other transforms that want type-safe
> pointers.
> > - unsigned NumZeros = 0;
> > - while (SrcElTy && SrcElTy != DstElTy) {
> > - SrcElTy = GetElementPtrInst::getTypeAtIndex(SrcElTy, (uint64_t)0);
> > - ++NumZeros;
> > - }
> > -
> > - // If we found a path from the src to dest, create the
> getelementptr now.
> > - if (SrcElTy == DstElTy) {
> > - SmallVector<Value *, 8> Idxs(NumZeros + 1, Builder.getInt32(0));
> > - GetElementPtrInst *GEP =
> > - GetElementPtrInst::Create(SrcPTy->getElementType(), Src,
> Idxs);
> > -
> > - // If the source pointer is dereferenceable, then assume it
> points to an
> > - // allocated object and apply "inbounds" to the GEP.
> > - bool CanBeNull, CanBeFreed;
> > - if (Src->getPointerDereferenceableBytes(DL, CanBeNull,
> CanBeFreed)) {
> > - // In a non-default address space (not 0), a null pointer can
> not be
> > - // assumed inbounds, so ignore that case
> (dereferenceable_or_null).
> > - // The reason is that 'null' is not treated
> > diff erently in these address
> > - // spaces, and we consequently ignore the 'gep inbounds'
> special case
> > - // for 'null' which allows 'inbounds' on 'null' if the indices
> are
> > - // zeros.
> > - if (SrcPTy->getAddressSpace() == 0 || !CanBeNull)
> > - GEP->setIsInBounds();
> > - }
> > - return GEP;
> > - }
> > + if (Instruction *I = convertBitCastToGEP(CI, Builder, DL))
> > + return I;
> > }
> >
> > if (FixedVectorType *DestVTy = dyn_cast<FixedVectorType>(DestTy)) {
> >
> >
> >
> > _______________________________________________
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> > llvm-commits at lists.llvm.org
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>
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