[llvm] [clang-tools-extra] [clang] [AArch64] Add an AArch64 pass for loop idiom transformations (PR #72273)
David Green via cfe-commits
cfe-commits at lists.llvm.org
Tue Dec 19 04:44:46 PST 2023
================
@@ -0,0 +1,816 @@
+//===- AArch64LoopIdiomTransform.cpp - Loop idiom recognition -------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass implements a pass that recognizes certain loop idioms and
+// transforms them into more optimized versions of the same loop. In cases
+// where this happens, it can be a significant performance win.
+//
+// We currently only recognize one loop that finds the first mismatched byte
+// in an array and returns the index, i.e. something like:
+//
+// while (++i != n) {
+// if (a[i] != b[i])
+// break;
+// }
+//
+// In this example we can actually vectorize the loop despite the early exit,
+// although the loop vectorizer does not support it. It requires some extra
+// checks to deal with the possibility of faulting loads when crossing page
+// boundaries. However, even with these checks it is still profitable to do the
+// transformation.
+//
+//===----------------------------------------------------------------------===//
+//
+// TODO List:
+//
+// * When optimizing for code size we may want to avoid some transformations.
+// * We can also support the inverse case where we scan for a matching element.
+//
+//===----------------------------------------------------------------------===//
+
+#include "AArch64LoopIdiomTransform.h"
+#include "llvm/Analysis/DomTreeUpdater.h"
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/MDBuilder.h"
+#include "llvm/IR/PatternMatch.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "aarch64-loop-idiom-transform"
+
+static cl::opt<bool>
+ DisableAll("disable-aarch64-lit-all", cl::Hidden, cl::init(false),
+ cl::desc("Disable AArch64 Loop Idiom Transform Pass."));
+
+static cl::opt<bool> DisableByteCmp(
+ "disable-aarch64-lit-bytecmp", cl::Hidden, cl::init(false),
+ cl::desc("Proceed with AArch64 Loop Idiom Transform Pass, but do "
+ "not convert byte-compare loop(s)."));
+
+static cl::opt<bool> VerifyLoops(
+ "aarch64-lit-verify", cl::Hidden, cl::init(false),
+ cl::desc("Verify loops generated AArch64 Loop Idiom Transform Pass."));
+
+namespace llvm {
+
+void initializeAArch64LoopIdiomTransformLegacyPassPass(PassRegistry &);
+Pass *createAArch64LoopIdiomTransformPass();
+
+} // end namespace llvm
+
+namespace {
+
+class AArch64LoopIdiomTransform {
+ Loop *CurLoop = nullptr;
+ DominatorTree *DT;
+ LoopInfo *LI;
+ const TargetTransformInfo *TTI;
+ const DataLayout *DL;
+
+public:
+ explicit AArch64LoopIdiomTransform(DominatorTree *DT, LoopInfo *LI,
+ const TargetTransformInfo *TTI,
+ const DataLayout *DL)
+ : DT(DT), LI(LI), TTI(TTI), DL(DL) {}
+
+ bool run(Loop *L);
+
+private:
+ /// \name Countable Loop Idiom Handling
+ /// @{
+
+ bool runOnCountableLoop();
+ bool runOnLoopBlock(BasicBlock *BB, const SCEV *BECount,
+ SmallVectorImpl<BasicBlock *> &ExitBlocks);
+
+ bool recognizeByteCompare();
+ Value *expandFindMismatch(IRBuilder<> &Builder, GetElementPtrInst *GEPA,
+ GetElementPtrInst *GEPB, Instruction *Index,
+ Value *Start, Value *MaxLen);
+ void transformByteCompare(GetElementPtrInst *GEPA, GetElementPtrInst *GEPB,
+ PHINode *IndPhi, Value *MaxLen, Instruction *Index,
+ Value *Start, bool IncIdx, BasicBlock *FoundBB,
+ BasicBlock *EndBB);
+ /// @}
+};
+
+class AArch64LoopIdiomTransformLegacyPass : public LoopPass {
+public:
+ static char ID;
+
+ explicit AArch64LoopIdiomTransformLegacyPass() : LoopPass(ID) {
+ initializeAArch64LoopIdiomTransformLegacyPassPass(
+ *PassRegistry::getPassRegistry());
+ }
+
+ StringRef getPassName() const override {
+ return "Transform AArch64-specific loop idioms";
+ }
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.addRequired<LoopInfoWrapperPass>();
+ AU.addRequired<DominatorTreeWrapperPass>();
+ AU.addRequired<TargetTransformInfoWrapperPass>();
+ }
+
+ bool runOnLoop(Loop *L, LPPassManager &LPM) override;
+};
+
+bool AArch64LoopIdiomTransformLegacyPass::runOnLoop(Loop *L,
+ LPPassManager &LPM) {
+
+ if (skipLoop(L))
+ return false;
+
+ auto *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+ auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
+ auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(
+ *L->getHeader()->getParent());
+ return AArch64LoopIdiomTransform(
+ DT, LI, &TTI, &L->getHeader()->getModule()->getDataLayout())
+ .run(L);
+}
+
+} // end anonymous namespace
+
+char AArch64LoopIdiomTransformLegacyPass::ID = 0;
+
+INITIALIZE_PASS_BEGIN(
+ AArch64LoopIdiomTransformLegacyPass, "aarch64-lit",
+ "Transform specific loop idioms into optimized vector forms", false, false)
+INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
+INITIALIZE_PASS_DEPENDENCY(LCSSAWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
+INITIALIZE_PASS_END(
+ AArch64LoopIdiomTransformLegacyPass, "aarch64-lit",
+ "Transform specific loop idioms into optimized vector forms", false, false)
+
+Pass *llvm::createAArch64LoopIdiomTransformPass() {
+ return new AArch64LoopIdiomTransformLegacyPass();
+}
+
+PreservedAnalyses
+AArch64LoopIdiomTransformPass::run(Loop &L, LoopAnalysisManager &AM,
+ LoopStandardAnalysisResults &AR,
+ LPMUpdater &) {
+ if (DisableAll)
+ return PreservedAnalyses::all();
+
+ const auto *DL = &L.getHeader()->getModule()->getDataLayout();
+
+ AArch64LoopIdiomTransform LIT(&AR.DT, &AR.LI, &AR.TTI, DL);
+ if (!LIT.run(&L))
+ return PreservedAnalyses::all();
+
+ return PreservedAnalyses::none();
+}
+
+//===----------------------------------------------------------------------===//
+//
+// Implementation of AArch64LoopIdiomTransform
+//
+//===----------------------------------------------------------------------===//
+
+bool AArch64LoopIdiomTransform::run(Loop *L) {
+ CurLoop = L;
+
+ if (DisableAll)
+ return false;
+
+ // If the loop could not be converted to canonical form, it must have an
+ // indirectbr in it, just give up.
+ if (!L->getLoopPreheader())
+ return false;
+
+ LLVM_DEBUG(dbgs() << DEBUG_TYPE " Scanning: F["
+ << CurLoop->getHeader()->getParent()->getName()
+ << "] Loop %" << CurLoop->getHeader()->getName() << "\n");
+
+ return recognizeByteCompare();
+}
+
+
+bool AArch64LoopIdiomTransform::recognizeByteCompare() {
+ // Currently the transformation only works on scalable vector types, although
+ // there is no fundamental reason why it cannot be made to work for fixed
+ // width too.
+
+ // We also need to know the minimum page size for the target in order to
+ // generate runtime memory checks to ensure the vector version won't fault.
+ if (!TTI->supportsScalableVectors() || !TTI->getMinPageSize().has_value() ||
+ DisableByteCmp)
+ return false;
+
+ BasicBlock *Header = CurLoop->getHeader();
+
+ // In AArch64LoopIdiomTransform::run we have already checked that the loop
+ // has a preheader so we can assume it's in a canonical form.
+ if (CurLoop->getNumBackEdges() != 1 || CurLoop->getNumBlocks() != 2)
+ return false;
+
+ PHINode *PN = dyn_cast<PHINode>(&Header->front());
+ if (!PN || PN->getNumIncomingValues() != 2)
+ return false;
+
+ auto LoopBlocks = CurLoop->getBlocks();
+ // The first block in the loop should contain only 4 instructions, e.g.
+ //
+ // while.cond:
+ // %res.phi = phi i32 [ %start, %ph ], [ %inc, %while.body ]
+ // %inc = add i32 %res.phi, 1
+ // %cmp.not = icmp eq i32 %inc, %n
+ // br i1 %cmp.not, label %while.end, label %while.body
+ //
+ auto CondBBInsts = LoopBlocks[0]->instructionsWithoutDebug();
+ if (std::distance(CondBBInsts.begin(), CondBBInsts.end()) > 4)
+ return false;
+
+ // The second block should contain 7 instructions, e.g.
+ //
+ // while.body:
+ // %idx = zext i32 %inc to i64
+ // %idx.a = getelementptr inbounds i8, ptr %a, i64 %idx
+ // %load.a = load i8, ptr %idx.a
+ // %idx.b = getelementptr inbounds i8, ptr %b, i64 %idx
+ // %load.b = load i8, ptr %idx.b
+ // %cmp.not.ld = icmp eq i8 %load.a, %load.b
+ // br i1 %cmp.not.ld, label %while.cond, label %while.end
+ //
+ auto LoopBBInsts = LoopBlocks[1]->instructionsWithoutDebug();
+ if (std::distance(LoopBBInsts.begin(), LoopBBInsts.end()) > 7)
+ return false;
+
+ using namespace PatternMatch;
+
+ // The incoming value to the PHI node from the loop should be an add of 1.
+ Value *StartIdx = nullptr;
+ Instruction *Index = nullptr;
+ if (!CurLoop->contains(PN->getIncomingBlock(0))) {
+ StartIdx = PN->getIncomingValue(0);
+ Index = dyn_cast<Instruction>(PN->getIncomingValue(1));
+ } else {
+ StartIdx = PN->getIncomingValue(1);
+ Index = dyn_cast<Instruction>(PN->getIncomingValue(0));
+ }
+
+ // Limit to 32-bit types for now
+ if (!Index || !Index->getType()->isIntegerTy(32) ||
+ !match(Index, m_c_Add(m_Specific(PN), m_One())))
+ return false;
+
+ // If we match the pattern, PN and Index will be replaced with the result of
+ // the cttz.elts intrinsic. If any other instructions are used outside of
+ // the loop, we cannot replace it.
+ for (BasicBlock *BB : LoopBlocks)
+ for (Instruction &I : *BB)
+ if (&I != PN && &I != Index)
+ for (User *U : I.users())
+ if (!CurLoop->contains(cast<Instruction>(U)))
+ return false;
+
+ // Match the branch instruction for the header
+ ICmpInst::Predicate Pred;
+ Value *MaxLen;
+ BasicBlock *EndBB, *WhileBB;
+ if (!match(Header->getTerminator(),
+ m_Br(m_ICmp(Pred, m_Specific(Index), m_Value(MaxLen)),
+ m_BasicBlock(EndBB), m_BasicBlock(WhileBB))) ||
+ Pred != ICmpInst::Predicate::ICMP_EQ || !CurLoop->contains(WhileBB))
+ return false;
+
+ // WhileBB should contain the pattern of load & compare instructions. Match
+ // the pattern and find the GEP instructions used by the loads.
+ ICmpInst::Predicate WhilePred;
+ BasicBlock *FoundBB;
+ BasicBlock *TrueBB;
+ Value *LoadA, *LoadB;
+ if (!match(WhileBB->getTerminator(),
+ m_Br(m_ICmp(WhilePred, m_Value(LoadA), m_Value(LoadB)),
+ m_BasicBlock(TrueBB), m_BasicBlock(FoundBB))) ||
+ WhilePred != ICmpInst::Predicate::ICMP_EQ || !CurLoop->contains(TrueBB))
+ return false;
+
+ Value *A, *B;
+ if (!match(LoadA, m_Load(m_Value(A))) || !match(LoadB, m_Load(m_Value(B))))
+ return false;
+
+ GetElementPtrInst *GEPA = dyn_cast<GetElementPtrInst>(A);
+ GetElementPtrInst *GEPB = dyn_cast<GetElementPtrInst>(B);
+
+ if (!GEPA || !GEPB)
+ return false;
+
+ Value *PtrA = GEPA->getPointerOperand();
+ Value *PtrB = GEPB->getPointerOperand();
+
+ // Check we are loading i8 values from two loop invariant pointers
+ if (!CurLoop->isLoopInvariant(PtrA) || !CurLoop->isLoopInvariant(PtrB) ||
+ !GEPA->getResultElementType()->isIntegerTy(8) ||
+ !GEPB->getResultElementType()->isIntegerTy(8) ||
+ !cast<LoadInst>(LoadA)->getType()->isIntegerTy(8) ||
+ !cast<LoadInst>(LoadB)->getType()->isIntegerTy(8) || PtrA == PtrB)
+ return false;
+
+ // Check that the index to the GEPs is the index we found earlier
+ if (GEPA->getNumIndices() > 1 || GEPB->getNumIndices() > 1)
+ return false;
+
+ Value *IdxA = GEPA->getOperand(GEPA->getNumIndices());
+ Value *IdxB = GEPB->getOperand(GEPB->getNumIndices());
+ if (IdxA != IdxB || !match(IdxA, m_ZExt(m_Specific(Index))))
+ return false;
+
+ // Ensure that when the Found and End blocks are identical the PHIs have the
+ // supported format. We don't currently allow cases like this:
+ // while.cond:
+ // ...
+ // br i1 %cmp.not, label %while.end, label %while.body
+ //
+ // while.body:
+ // ...
+ // br i1 %cmp.not2, label %while.cond, label %while.end
+ //
+ // while.end:
+ // %final_ptr = phi ptr [ %c, %while.body ], [ %d, %while.cond ]
+ //
+ // Where the incoming values for %final_ptr are unique and from each of the
+ // loop blocks, but not actually defined in the loop. This requires extra
+ // work setting up the byte.compare block, i.e. by introducing a select to
+ // choose the correct value.
+ // TODO: We could add support for this in future.
+ if (FoundBB == EndBB) {
+ for (PHINode &PN : EndBB->phis()) {
+ Value *LastValue = nullptr;
+ for (unsigned I = 0; I < PN.getNumIncomingValues(); I++) {
+ BasicBlock *BB = PN.getIncomingBlock(I);
+ if (CurLoop->contains(BB)) {
+ Value *V = PN.getIncomingValue(I);
+ if (!LastValue)
+ LastValue = V;
+ else if (LastValue != V)
+ return false;
+ }
+ }
+ }
+ }
+
+ LLVM_DEBUG(dbgs() << "FOUND IDIOM IN LOOP: \n"
+ << *(EndBB->getParent()) << "\n\n");
+
+ // The index is incremented before the GEP/Load pair so we need to
+ // add 1 to the start value.
+ transformByteCompare(GEPA, GEPB, PN, MaxLen, Index, StartIdx, /*IncIdx=*/true,
+ FoundBB, EndBB);
+ return true;
+}
+
+Value *AArch64LoopIdiomTransform::expandFindMismatch(
+ IRBuilder<> &Builder, GetElementPtrInst *GEPA, GetElementPtrInst *GEPB,
+ Instruction *Index, Value *Start, Value *MaxLen) {
+ Value *PtrA = GEPA->getPointerOperand();
+ Value *PtrB = GEPB->getPointerOperand();
+
+ // Get the arguments and types for the intrinsic.
+ BasicBlock *Preheader = CurLoop->getLoopPreheader();
+ BranchInst *PHBranch = cast<BranchInst>(Preheader->getTerminator());
+ LLVMContext &Ctx = PHBranch->getContext();
+ Type *LoadType = Type::getInt8Ty(Ctx);
+ Type *ResType = Builder.getInt32Ty();
+
+ // Split block in the original loop preheader.
+ DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
+ BasicBlock *EndBlock =
+ SplitBlock(Preheader, PHBranch, DT, LI, nullptr, "mismatch_end");
+
+ // Create the blocks that we're going to need:
+ // 1. A block for checking the zero-extended length exceeds 0
+ // 2. A block to check that the start and end addresses of a given array
+ // lie on the same page.
+ // 3. The SVE loop preheader.
+ // 4. The first SVE loop block.
+ // 5. The SVE loop increment block.
+ // 6. A block we can jump to from the SVE loop when a mismatch is found.
+ // 7. The first block of the scalar loop itself, containing PHIs , loads
+ // and cmp.
+ // 8. A scalar loop increment block to increment the PHIs and go back
+ // around the loop.
+
+ BasicBlock *MinItCheckBlock = BasicBlock::Create(
+ Ctx, "mismatch_min_it_check", EndBlock->getParent(), EndBlock);
+
+ // Update the terminator added by SplitBlock to branch to the first block
+ Preheader->getTerminator()->setSuccessor(0, MinItCheckBlock);
+
+ BasicBlock *MemCheckBlock = BasicBlock::Create(
+ Ctx, "mismatch_mem_check", EndBlock->getParent(), EndBlock);
+
+ BasicBlock *SVELoopPreheaderBlock = BasicBlock::Create(
+ Ctx, "mismatch_sve_loop_preheader", EndBlock->getParent(), EndBlock);
+
+ BasicBlock *SVELoopStartBlock = BasicBlock::Create(
+ Ctx, "mismatch_sve_loop", EndBlock->getParent(), EndBlock);
+
+ BasicBlock *SVELoopIncBlock = BasicBlock::Create(
+ Ctx, "mismatch_sve_loop_inc", EndBlock->getParent(), EndBlock);
+
+ BasicBlock *SVELoopMismatchBlock = BasicBlock::Create(
+ Ctx, "mismatch_sve_loop_found", EndBlock->getParent(), EndBlock);
+
+ BasicBlock *LoopPreHeaderBlock = BasicBlock::Create(
+ Ctx, "mismatch_loop_pre", EndBlock->getParent(), EndBlock);
+
+ BasicBlock *LoopStartBlock =
+ BasicBlock::Create(Ctx, "mismatch_loop", EndBlock->getParent(), EndBlock);
+
+ BasicBlock *LoopIncBlock = BasicBlock::Create(
+ Ctx, "mismatch_loop_inc", EndBlock->getParent(), EndBlock);
+
+ DTU.applyUpdates({{DominatorTree::Insert, Preheader, MinItCheckBlock},
+ {DominatorTree::Delete, Preheader, EndBlock}});
+
+ // Update LoopInfo with the new SVE & scalar loops.
+ auto SVELoop = LI->AllocateLoop();
+ auto ScalarLoop = LI->AllocateLoop();
+
+ if (CurLoop->getParentLoop()) {
+ CurLoop->getParentLoop()->addBasicBlockToLoop(MinItCheckBlock, *LI);
+ CurLoop->getParentLoop()->addBasicBlockToLoop(MemCheckBlock, *LI);
+ CurLoop->getParentLoop()->addBasicBlockToLoop(SVELoopPreheaderBlock, *LI);
+ CurLoop->getParentLoop()->addChildLoop(SVELoop);
+ CurLoop->getParentLoop()->addBasicBlockToLoop(SVELoopMismatchBlock, *LI);
+ CurLoop->getParentLoop()->addBasicBlockToLoop(LoopPreHeaderBlock, *LI);
+ CurLoop->getParentLoop()->addChildLoop(ScalarLoop);
+ } else {
+ LI->addTopLevelLoop(SVELoop);
+ LI->addTopLevelLoop(ScalarLoop);
+ }
+
+ // Add the new basic blocks to their associated loops.
+ SVELoop->addBasicBlockToLoop(SVELoopStartBlock, *LI);
+ SVELoop->addBasicBlockToLoop(SVELoopIncBlock, *LI);
+
+ ScalarLoop->addBasicBlockToLoop(LoopStartBlock, *LI);
+ ScalarLoop->addBasicBlockToLoop(LoopIncBlock, *LI);
+
+ // Set up some types and constants that we intend to reuse.
+ Type *I64Type = Builder.getInt64Ty();
+
+ // Check the zero-extended iteration count > 0
+ Builder.SetInsertPoint(MinItCheckBlock);
+ Value *ExtStart = Builder.CreateZExt(Start, I64Type);
+ Value *ExtEnd = Builder.CreateZExt(MaxLen, I64Type);
+ // This check doesn't really cost us very much.
+
+ Value *LimitCheck = Builder.CreateICmpULE(Start, MaxLen);
+ BranchInst *MinItCheckBr =
+ BranchInst::Create(MemCheckBlock, LoopPreHeaderBlock, LimitCheck);
+ MinItCheckBr->setMetadata(
+ LLVMContext::MD_prof,
+ MDBuilder(MinItCheckBr->getContext()).createBranchWeights(99, 1));
+ Builder.Insert(MinItCheckBr);
+
+ DTU.applyUpdates(
+ {{DominatorTree::Insert, MinItCheckBlock, MemCheckBlock},
+ {DominatorTree::Insert, MinItCheckBlock, LoopPreHeaderBlock}});
+
+ // For each of the arrays, check the start/end addresses are on the same
+ // page.
+ Builder.SetInsertPoint(MemCheckBlock);
+
+ // The early exit in the original loop means that when performing vector
+ // loads we are potentially reading ahead of the early exit. So we could
+ // fault if crossing a page boundary. Therefore, we create runtime memory
+ // checks based on the minimum page size as follows:
+ // 1. Calculate the addresses of the first memory accesses in the loop,
+ // i.e. LhsStart and RhsStart.
+ // 2. Get the last accessed addresses in the loop, i.e. LhsEnd and RhsEnd.
+ // 3. Determine which pages correspond to all the memory accesses, i.e
+ // LhsStartPage, LhsEndPage, RhsStartPage, RhsEndPage.
+ // 4. If LhsStartPage == LhsEndPage and RhsStartPage == RhsEndPage, then
+ // we know we won't cross any page boundaries in the loop so we can
+ // enter the vector loop! Otherwise we fall back on the scalar loop.
+ Value *LhsStartGEP = Builder.CreateGEP(LoadType, PtrA, ExtStart);
+ Value *RhsStartGEP = Builder.CreateGEP(LoadType, PtrB, ExtStart);
+ Value *RhsStart = Builder.CreatePtrToInt(RhsStartGEP, I64Type);
+ Value *LhsStart = Builder.CreatePtrToInt(LhsStartGEP, I64Type);
+ Value *LhsEndGEP = Builder.CreateGEP(LoadType, PtrA, ExtEnd);
+ Value *RhsEndGEP = Builder.CreateGEP(LoadType, PtrB, ExtEnd);
+ Value *LhsEnd = Builder.CreatePtrToInt(LhsEndGEP, I64Type);
+ Value *RhsEnd = Builder.CreatePtrToInt(RhsEndGEP, I64Type);
+
+ const uint64_t MinPageSize = TTI->getMinPageSize().value();
+ const uint64_t AddrShiftAmt = llvm::Log2_64(MinPageSize);
+ Value *LhsStartPage = Builder.CreateLShr(LhsStart, AddrShiftAmt);
+ Value *LhsEndPage = Builder.CreateLShr(LhsEnd, AddrShiftAmt);
+ Value *RhsStartPage = Builder.CreateLShr(RhsStart, AddrShiftAmt);
+ Value *RhsEndPage = Builder.CreateLShr(RhsEnd, AddrShiftAmt);
+ Value *LhsPageCmp = Builder.CreateICmpNE(LhsStartPage, LhsEndPage);
+ Value *RhsPageCmp = Builder.CreateICmpNE(RhsStartPage, RhsEndPage);
+
+ Value *CombinedPageCmp = Builder.CreateOr(LhsPageCmp, RhsPageCmp);
+ BranchInst *CombinedPageCmpCmpBr = BranchInst::Create(
+ LoopPreHeaderBlock, SVELoopPreheaderBlock, CombinedPageCmp);
+ CombinedPageCmpCmpBr->setMetadata(
+ LLVMContext::MD_prof, MDBuilder(CombinedPageCmpCmpBr->getContext())
+ .createBranchWeights(10, 90));
+ Builder.Insert(CombinedPageCmpCmpBr);
+
+ DTU.applyUpdates(
+ {{DominatorTree::Insert, MemCheckBlock, LoopPreHeaderBlock},
+ {DominatorTree::Insert, MemCheckBlock, SVELoopPreheaderBlock}});
+
+ // Set up the SVE loop preheader, i.e. calculate initial loop predicate,
+ // zero-extend MaxLen to 64-bits, determine the number of vector elements
+ // processed in each iteration, etc.
+ Builder.SetInsertPoint(SVELoopPreheaderBlock);
+
+ // At this point we know two things must be true:
+ // 1. Start <= End
+ // 2. ExtMaxLen <= MinPageSize due to the page checks.
+ // Therefore, we know that we can use a 64-bit induction variable that
+ // starts from 0 -> ExtMaxLen and it will not overflow.
+ ScalableVectorType *PredVTy =
+ ScalableVectorType::get(Builder.getInt1Ty(), 16);
+
+ Value *InitialPred = Builder.CreateIntrinsic(
+ Intrinsic::get_active_lane_mask, {PredVTy, I64Type}, {ExtStart, ExtEnd});
+
+ Value *VecLen = Builder.CreateIntrinsic(Intrinsic::vscale, {I64Type}, {});
+ VecLen = Builder.CreateMul(VecLen, ConstantInt::get(I64Type, 16), "",
+ /*HasNUW=*/true, /*HasNSW=*/true);
+
+ Value *PFalse = Builder.CreateVectorSplat(PredVTy->getElementCount(),
+ Builder.getInt1(false));
+
+ BranchInst *JumpToSVELoop = BranchInst::Create(SVELoopStartBlock);
+ Builder.Insert(JumpToSVELoop);
+
+ DTU.applyUpdates(
+ {{DominatorTree::Insert, SVELoopPreheaderBlock, SVELoopStartBlock}});
+
+ // Set up the first SVE loop block by creating the PHIs, doing the vector
+ // loads and comparing the vectors.
+ Builder.SetInsertPoint(SVELoopStartBlock);
+ PHINode *LoopPred = Builder.CreatePHI(PredVTy, 2, "mismatch_sve_loop_pred");
+ LoopPred->addIncoming(InitialPred, SVELoopPreheaderBlock);
+ PHINode *SVEIndexPhi = Builder.CreatePHI(I64Type, 2, "mismatch_sve_index");
+ SVEIndexPhi->addIncoming(ExtStart, SVELoopPreheaderBlock);
+ Type *SVELoadType = ScalableVectorType::get(Builder.getInt8Ty(), 16);
+ Value *GepOffset = SVEIndexPhi;
----------------
davemgreen wrote:
This variable isn't needed?
https://github.com/llvm/llvm-project/pull/72273
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