[llvm] r209788 - [x86] Fold extract_vector_elt of a load into the Load's address computation.
Robert Khasanov
rob.khasanov at gmail.com
Thu Jul 17 10:07:04 PDT 2014
Michael,
Could you provide conservative fix for this bug?
2014-07-12 2:07 GMT+04:00 Michael Spencer <bigcheesegs at gmail.com>:
> On Fri, Jul 11, 2014 at 12:47 PM, Michael Spencer <bigcheesegs at gmail.com>
> wrote:
> > On Fri, Jul 11, 2014 at 5:36 AM, Dmitry Babokin <babokin at gmail.com>
> wrote:
> >> Michael,
> >>
> >> Your commit caused a regression described in bug 20115, could you have a
> >> look?
> >>
> >> Dmitry
> >
> > Investigating now. Thanks for letting me know.
> >
> > - Michael Spencer
>
> It seems that it creates a dependency loop by moving the use of
> %POINT_VALUE from the extractelement up to the original load across
> the lifetime end marker. In this specific case that would be fine if
> the chains were fixed, but I don't believe it's always valid. I think
> the conservative fix here is to not do this optimization if you would
> have to move a load or an operation with possible side effects.
>
> - Michael Spencer
>
> >
> >>
> >>
> >> On Thu, May 29, 2014 at 5:42 AM, Michael J. Spencer <
> bigcheesegs at gmail.com>
> >> wrote:
> >>>
> >>> Author: mspencer
> >>> Date: Wed May 28 20:42:45 2014
> >>> New Revision: 209788
> >>>
> >>> URL: http://llvm.org/viewvc/llvm-project?rev=209788&view=rev
> >>> Log:
> >>> [x86] Fold extract_vector_elt of a load into the Load's address
> >>> computation.
> >>>
> >>> An address only use of an extract element of a load can be simplified
> to a
> >>> load. Without this the result of the extract element is spilled to the
> >>> stack so that an address is available.
> >>>
> >>> Modified:
> >>> llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
> >>> llvm/trunk/test/CodeGen/X86/vec_splat.ll
> >>>
> >>> Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
> >>> URL:
> >>>
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=209788&r1=209787&r2=209788&view=diff
> >>>
> >>>
> ==============================================================================
> >>> --- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
> >>> +++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Wed May 28
> >>> 20:42:45 2014
> >>> @@ -169,6 +169,16 @@ namespace {
> >>> bool CombineToPostIndexedLoadStore(SDNode *N);
> >>> bool SliceUpLoad(SDNode *N);
> >>>
> >>> + /// \brief Replace an ISD::EXTRACT_VECTOR_ELT of a load with a
> >>> narrowed
> >>> + /// load.
> >>> + ///
> >>> + /// \param EVE ISD::EXTRACT_VECTOR_ELT to be replaced.
> >>> + /// \param InVecVT type of the input vector to EVE with bitcasts
> >>> resolved.
> >>> + /// \param EltNo index of the vector element to load.
> >>> + /// \param OriginalLoad load that EVE came from to be replaced.
> >>> + /// \returns EVE on success SDValue() on failure.
> >>> + SDValue ReplaceExtractVectorEltOfLoadWithNarrowedLoad(
> >>> + SDNode *EVE, EVT InVecVT, SDValue EltNo, LoadSDNode
> >>> *OriginalLoad);
> >>> void ReplaceLoadWithPromotedLoad(SDNode *Load, SDNode *ExtLoad);
> >>> SDValue PromoteOperand(SDValue Op, EVT PVT, bool &Replace);
> >>> SDValue SExtPromoteOperand(SDValue Op, EVT PVT);
> >>> @@ -9675,6 +9685,86 @@ SDValue DAGCombiner::visitINSERT_VECTOR_
> >>> return DAG.getNode(ISD::BUILD_VECTOR, dl, VT, Ops);
> >>> }
> >>>
> >>> +SDValue DAGCombiner::ReplaceExtractVectorEltOfLoadWithNarrowedLoad(
> >>> + SDNode *EVE, EVT InVecVT, SDValue EltNo, LoadSDNode
> *OriginalLoad) {
> >>> + EVT ResultVT = EVE->getValueType(0);
> >>> + EVT VecEltVT = InVecVT.getVectorElementType();
> >>> + unsigned Align = OriginalLoad->getAlignment();
> >>> + unsigned NewAlign = TLI.getDataLayout()->getABITypeAlignment(
> >>> + VecEltVT.getTypeForEVT(*DAG.getContext()));
> >>> +
> >>> + if (NewAlign > Align || !TLI.isOperationLegalOrCustom(ISD::LOAD,
> >>> VecEltVT))
> >>> + return SDValue();
> >>> +
> >>> + Align = NewAlign;
> >>> +
> >>> + SDValue NewPtr = OriginalLoad->getBasePtr();
> >>> + SDValue Offset;
> >>> + EVT PtrType = NewPtr.getValueType();
> >>> + MachinePointerInfo MPI;
> >>> + if (auto *ConstEltNo = dyn_cast<ConstantSDNode>(EltNo)) {
> >>> + int Elt = ConstEltNo->getZExtValue();
> >>> + unsigned PtrOff = VecEltVT.getSizeInBits() * Elt / 8;
> >>> + if (TLI.isBigEndian())
> >>> + PtrOff = InVecVT.getSizeInBits() / 8 - PtrOff;
> >>> + Offset = DAG.getConstant(PtrOff, PtrType);
> >>> + MPI = OriginalLoad->getPointerInfo().getWithOffset(PtrOff);
> >>> + } else {
> >>> + Offset = DAG.getNode(
> >>> + ISD::MUL, SDLoc(EVE), EltNo.getValueType(), EltNo,
> >>> + DAG.getConstant(VecEltVT.getStoreSize(),
> EltNo.getValueType()));
> >>> + if (TLI.isBigEndian())
> >>> + Offset = DAG.getNode(
> >>> + ISD::SUB, SDLoc(EVE), EltNo.getValueType(),
> >>> + DAG.getConstant(InVecVT.getStoreSize(),
> EltNo.getValueType()),
> >>> Offset);
> >>> + MPI = OriginalLoad->getPointerInfo();
> >>> + }
> >>> + NewPtr = DAG.getNode(ISD::ADD, SDLoc(EVE), PtrType, NewPtr, Offset);
> >>> +
> >>> + // The replacement we need to do here is a little tricky: we need to
> >>> + // replace an extractelement of a load with a load.
> >>> + // Use ReplaceAllUsesOfValuesWith to do the replacement.
> >>> + // Note that this replacement assumes that the extractvalue is the
> only
> >>> + // use of the load; that's okay because we don't want to perform
> this
> >>> + // transformation in other cases anyway.
> >>> + SDValue Load;
> >>> + SDValue Chain;
> >>> + if (ResultVT.bitsGT(VecEltVT)) {
> >>> + // If the result type of vextract is wider than the load, then
> issue
> >>> an
> >>> + // extending load instead.
> >>> + ISD::LoadExtType ExtType = TLI.isLoadExtLegal(ISD::ZEXTLOAD,
> >>> VecEltVT)
> >>> + ? ISD::ZEXTLOAD
> >>> + : ISD::EXTLOAD;
> >>> + Load = DAG.getExtLoad(ExtType, SDLoc(EVE), ResultVT,
> >>> OriginalLoad->getChain(),
> >>> + NewPtr, MPI, VecEltVT,
> >>> OriginalLoad->isVolatile(),
> >>> + OriginalLoad->isNonTemporal(), Align,
> >>> + OriginalLoad->getTBAAInfo());
> >>> + Chain = Load.getValue(1);
> >>> + } else {
> >>> + Load = DAG.getLoad(
> >>> + VecEltVT, SDLoc(EVE), OriginalLoad->getChain(), NewPtr, MPI,
> >>> + OriginalLoad->isVolatile(), OriginalLoad->isNonTemporal(),
> >>> + OriginalLoad->isInvariant(), Align,
> OriginalLoad->getTBAAInfo());
> >>> + Chain = Load.getValue(1);
> >>> + if (ResultVT.bitsLT(VecEltVT))
> >>> + Load = DAG.getNode(ISD::TRUNCATE, SDLoc(EVE), ResultVT, Load);
> >>> + else
> >>> + Load = DAG.getNode(ISD::BITCAST, SDLoc(EVE), ResultVT, Load);
> >>> + }
> >>> + WorkListRemover DeadNodes(*this);
> >>> + SDValue From[] = { SDValue(EVE, 0), SDValue(OriginalLoad, 1) };
> >>> + SDValue To[] = { Load, Chain };
> >>> + DAG.ReplaceAllUsesOfValuesWith(From, To, 2);
> >>> + // Since we're explicitly calling ReplaceAllUses, add the new node
> to
> >>> the
> >>> + // worklist explicitly as well.
> >>> + AddToWorkList(Load.getNode());
> >>> + AddUsersToWorkList(Load.getNode()); // Add users too
> >>> + // Make sure to revisit this node to clean it up; it will usually be
> >>> dead.
> >>> + AddToWorkList(EVE);
> >>> + ++OpsNarrowed;
> >>> + return SDValue(EVE, 0);
> >>> +}
> >>> +
> >>> SDValue DAGCombiner::visitEXTRACT_VECTOR_ELT(SDNode *N) {
> >>> // (vextract (scalar_to_vector val, 0) -> val
> >>> SDValue InVec = N->getOperand(0);
> >>> @@ -9743,6 +9833,38 @@ SDValue DAGCombiner::visitEXTRACT_VECTOR
> >>> }
> >>> }
> >>>
> >>> + bool BCNumEltsChanged = false;
> >>> + EVT ExtVT = VT.getVectorElementType();
> >>> + EVT LVT = ExtVT;
> >>> +
> >>> + // If the result of load has to be truncated, then it's not
> necessarily
> >>> + // profitable.
> >>> + if (NVT.bitsLT(LVT) && !TLI.isTruncateFree(LVT, NVT))
> >>> + return SDValue();
> >>> +
> >>> + if (InVec.getOpcode() == ISD::BITCAST) {
> >>> + // Don't duplicate a load with other uses.
> >>> + if (!InVec.hasOneUse())
> >>> + return SDValue();
> >>> +
> >>> + EVT BCVT = InVec.getOperand(0).getValueType();
> >>> + if (!BCVT.isVector() || ExtVT.bitsGT(BCVT.getVectorElementType()))
> >>> + return SDValue();
> >>> + if (VT.getVectorNumElements() != BCVT.getVectorNumElements())
> >>> + BCNumEltsChanged = true;
> >>> + InVec = InVec.getOperand(0);
> >>> + ExtVT = BCVT.getVectorElementType();
> >>> + }
> >>> +
> >>> + // (vextract (vN[if]M load $addr), i) -> ([if]M load $addr + i *
> size)
> >>> + if (!LegalOperations && !ConstEltNo && InVec.hasOneUse() &&
> >>> + ISD::isNormalLoad(InVec.getNode())) {
> >>> + SDValue Index = N->getOperand(1);
> >>> + if (LoadSDNode *OrigLoad = dyn_cast<LoadSDNode>(InVec))
> >>> + return ReplaceExtractVectorEltOfLoadWithNarrowedLoad(N, VT,
> Index,
> >>> + OrigLoad);
> >>> + }
> >>> +
> >>> // Perform only after legalization to ensure build_vector /
> >>> vector_shuffle
> >>> // optimizations have already been done.
> >>> if (!LegalOperations) return SDValue();
> >>> @@ -9753,30 +9875,6 @@ SDValue DAGCombiner::visitEXTRACT_VECTOR
> >>>
> >>> if (ConstEltNo) {
> >>> int Elt = cast<ConstantSDNode>(EltNo)->getZExtValue();
> >>> - bool NewLoad = false;
> >>> - bool BCNumEltsChanged = false;
> >>> - EVT ExtVT = VT.getVectorElementType();
> >>> - EVT LVT = ExtVT;
> >>> -
> >>> - // If the result of load has to be truncated, then it's not
> >>> necessarily
> >>> - // profitable.
> >>> - if (NVT.bitsLT(LVT) && !TLI.isTruncateFree(LVT, NVT))
> >>> - return SDValue();
> >>> -
> >>> - if (InVec.getOpcode() == ISD::BITCAST) {
> >>> - // Don't duplicate a load with other uses.
> >>> - if (!InVec.hasOneUse())
> >>> - return SDValue();
> >>> -
> >>> - EVT BCVT = InVec.getOperand(0).getValueType();
> >>> - if (!BCVT.isVector() ||
> ExtVT.bitsGT(BCVT.getVectorElementType()))
> >>> - return SDValue();
> >>> - if (VT.getVectorNumElements() != BCVT.getVectorNumElements())
> >>> - BCNumEltsChanged = true;
> >>> - InVec = InVec.getOperand(0);
> >>> - ExtVT = BCVT.getVectorElementType();
> >>> - NewLoad = true;
> >>> - }
> >>>
> >>> LoadSDNode *LN0 = nullptr;
> >>> const ShuffleVectorSDNode *SVN = nullptr;
> >>> @@ -9819,6 +9917,7 @@ SDValue DAGCombiner::visitEXTRACT_VECTOR
> >>> if (ISD::isNormalLoad(InVec.getNode())) {
> >>> LN0 = cast<LoadSDNode>(InVec);
> >>> Elt = (Idx < (int)NumElems) ? Idx : Idx - (int)NumElems;
> >>> + EltNo = DAG.getConstant(Elt, EltNo.getValueType());
> >>> }
> >>> }
> >>>
> >>> @@ -9831,72 +9930,7 @@ SDValue DAGCombiner::visitEXTRACT_VECTOR
> >>> if (Elt == -1)
> >>> return DAG.getUNDEF(LVT);
> >>>
> >>> - unsigned Align = LN0->getAlignment();
> >>> - if (NewLoad) {
> >>> - // Check the resultant load doesn't need a higher alignment than
> >>> the
> >>> - // original load.
> >>> - unsigned NewAlign =
> >>> - TLI.getDataLayout()
> >>> -
> ->getABITypeAlignment(LVT.getTypeForEVT(*DAG.getContext()));
> >>> -
> >>> - if (NewAlign > Align || !TLI.isOperationLegalOrCustom(ISD::LOAD,
> >>> LVT))
> >>> - return SDValue();
> >>> -
> >>> - Align = NewAlign;
> >>> - }
> >>> -
> >>> - SDValue NewPtr = LN0->getBasePtr();
> >>> - unsigned PtrOff = 0;
> >>> -
> >>> - if (Elt) {
> >>> - PtrOff = LVT.getSizeInBits() * Elt / 8;
> >>> - EVT PtrType = NewPtr.getValueType();
> >>> - if (TLI.isBigEndian())
> >>> - PtrOff = VT.getSizeInBits() / 8 - PtrOff;
> >>> - NewPtr = DAG.getNode(ISD::ADD, SDLoc(N), PtrType, NewPtr,
> >>> - DAG.getConstant(PtrOff, PtrType));
> >>> - }
> >>> -
> >>> - // The replacement we need to do here is a little tricky: we need
> to
> >>> - // replace an extractelement of a load with a load.
> >>> - // Use ReplaceAllUsesOfValuesWith to do the replacement.
> >>> - // Note that this replacement assumes that the extractvalue is the
> >>> only
> >>> - // use of the load; that's okay because we don't want to perform
> this
> >>> - // transformation in other cases anyway.
> >>> - SDValue Load;
> >>> - SDValue Chain;
> >>> - if (NVT.bitsGT(LVT)) {
> >>> - // If the result type of vextract is wider than the load, then
> >>> issue an
> >>> - // extending load instead.
> >>> - ISD::LoadExtType ExtType = TLI.isLoadExtLegal(ISD::ZEXTLOAD,
> LVT)
> >>> - ? ISD::ZEXTLOAD : ISD::EXTLOAD;
> >>> - Load = DAG.getExtLoad(ExtType, SDLoc(N), NVT, LN0->getChain(),
> >>> - NewPtr,
> >>> LN0->getPointerInfo().getWithOffset(PtrOff),
> >>> - LVT, LN0->isVolatile(),
> LN0->isNonTemporal(),
> >>> - Align, LN0->getTBAAInfo());
> >>> - Chain = Load.getValue(1);
> >>> - } else {
> >>> - Load = DAG.getLoad(LVT, SDLoc(N), LN0->getChain(), NewPtr,
> >>> - LN0->getPointerInfo().getWithOffset(PtrOff),
> >>> - LN0->isVolatile(), LN0->isNonTemporal(),
> >>> - LN0->isInvariant(), Align,
> LN0->getTBAAInfo());
> >>> - Chain = Load.getValue(1);
> >>> - if (NVT.bitsLT(LVT))
> >>> - Load = DAG.getNode(ISD::TRUNCATE, SDLoc(N), NVT, Load);
> >>> - else
> >>> - Load = DAG.getNode(ISD::BITCAST, SDLoc(N), NVT, Load);
> >>> - }
> >>> - WorkListRemover DeadNodes(*this);
> >>> - SDValue From[] = { SDValue(N, 0), SDValue(LN0,1) };
> >>> - SDValue To[] = { Load, Chain };
> >>> - DAG.ReplaceAllUsesOfValuesWith(From, To, 2);
> >>> - // Since we're explcitly calling ReplaceAllUses, add the new node
> to
> >>> the
> >>> - // worklist explicitly as well.
> >>> - AddToWorkList(Load.getNode());
> >>> - AddUsersToWorkList(Load.getNode()); // Add users too
> >>> - // Make sure to revisit this node to clean it up; it will usually
> be
> >>> dead.
> >>> - AddToWorkList(N);
> >>> - return SDValue(N, 0);
> >>> + return ReplaceExtractVectorEltOfLoadWithNarrowedLoad(N, VT, EltNo,
> >>> LN0);
> >>> }
> >>>
> >>> return SDValue();
> >>>
> >>> Modified: llvm/trunk/test/CodeGen/X86/vec_splat.ll
> >>> URL:
> >>>
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/vec_splat.ll?rev=209788&r1=209787&r2=209788&view=diff
> >>>
> >>>
> ==============================================================================
> >>> --- llvm/trunk/test/CodeGen/X86/vec_splat.ll (original)
> >>> +++ llvm/trunk/test/CodeGen/X86/vec_splat.ll Wed May 28 20:42:45 2014
> >>> @@ -1,5 +1,6 @@
> >>> ; RUN: llc < %s -march=x86 -mcpu=pentium4 -mattr=+sse2 | FileCheck %s
> >>> -check-prefix=SSE2
> >>> ; RUN: llc < %s -march=x86 -mcpu=pentium4 -mattr=+sse3 | FileCheck %s
> >>> -check-prefix=SSE3
> >>> +; RUN: llc < %s -march=x86-64 -mattr=+avx | FileCheck %s
> >>> -check-prefix=AVX
> >>>
> >>> define void @test_v4sf(<4 x float>* %P, <4 x float>* %Q, float %X)
> >>> nounwind {
> >>> %tmp = insertelement <4 x float> zeroinitializer, float %X,
> i32 0
> >>> ; <<4 x float>> [#uses=1]
> >>> @@ -37,6 +38,23 @@ define void @test_v2sd(<2 x double>* %P,
> >>> define <4 x float> @load_extract_splat(<4 x float>* nocapture readonly
> >>> %ptr, i64 %i, i64 %j) nounwind {
> >>> %1 = getelementptr inbounds <4 x float>* %ptr, i64 %i
> >>> %2 = load <4 x float>* %1, align 16
> >>> + %3 = trunc i64 %j to i32
> >>> + %4 = extractelement <4 x float> %2, i32 %3
> >>> + %5 = insertelement <4 x float> undef, float %4, i32 0
> >>> + %6 = insertelement <4 x float> %5, float %4, i32 1
> >>> + %7 = insertelement <4 x float> %6, float %4, i32 2
> >>> + %8 = insertelement <4 x float> %7, float %4, i32 3
> >>> + ret <4 x float> %8
> >>> +
> >>> +; AVX-LABEL: load_extract_splat
> >>> +; AVX-NOT: rsp
> >>> +; AVX: vbroadcastss
> >>> +}
> >>> +
> >>> +; Fold extract of a load into the load's address computation. This
> avoids
> >>> spilling to the stack.
> >>> +define <4 x float> @load_extract_splat1(<4 x float>* nocapture
> readonly
> >>> %ptr, i64 %i, i64 %j) nounwind {
> >>> + %1 = getelementptr inbounds <4 x float>* %ptr, i64 %i
> >>> + %2 = load <4 x float>* %1, align 16
> >>> %3 = extractelement <4 x float> %2, i64 %j
> >>> %4 = insertelement <4 x float> undef, float %3, i32 0
> >>> %5 = insertelement <4 x float> %4, float %3, i32 1
> >>> @@ -44,7 +62,7 @@ define <4 x float> @load_extract_splat(<
> >>> %7 = insertelement <4 x float> %6, float %3, i32 3
> >>> ret <4 x float> %7
> >>>
> >>> -; AVX-LABEL: load_extract_splat
> >>> +; AVX-LABEL: load_extract_splat1
> >>> ; AVX-NOT: movs
> >>> ; AVX: vbroadcastss
> >>> }
> >>>
> >>>
> >>> _______________________________________________
> >>> llvm-commits mailing list
> >>> llvm-commits at cs.uiuc.edu
> >>> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
> >>
> >>
>
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