forked from OSchip/llvm-project
231 lines
8.0 KiB
C++
231 lines
8.0 KiB
C++
//===-------- PPCLoopDataPrefetch.cpp - Loop Data Prefetching Pass --------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements a Loop Data Prefetching Pass.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "ppc-loop-data-prefetch"
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#include "PPC.h"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/AssumptionCache.h"
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#include "llvm/Analysis/CodeMetrics.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/ScalarEvolution.h"
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#include "llvm/Analysis/ScalarEvolutionExpander.h"
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#include "llvm/Analysis/ScalarEvolutionExpressions.h"
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#include "llvm/Analysis/TargetTransformInfo.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/CFG.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/Module.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Transforms/Utils/ValueMapper.h"
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using namespace llvm;
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// By default, we limit this to creating 16 PHIs (which is a little over half
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// of the allocatable register set).
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static cl::opt<bool>
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PrefetchWrites("ppc-loop-prefetch-writes", cl::Hidden, cl::init(false),
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cl::desc("Prefetch write addresses"));
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// This seems like a reasonable default for the BG/Q (this pass is enabled, by
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// default, only on the BG/Q).
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static cl::opt<unsigned>
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PrefDist("ppc-loop-prefetch-distance", cl::Hidden, cl::init(300),
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cl::desc("The loop prefetch distance"));
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static cl::opt<unsigned>
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CacheLineSize("ppc-loop-prefetch-cache-line", cl::Hidden, cl::init(64),
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cl::desc("The loop prefetch cache line size"));
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namespace llvm {
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void initializePPCLoopDataPrefetchPass(PassRegistry&);
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}
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namespace {
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class PPCLoopDataPrefetch : public FunctionPass {
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public:
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static char ID; // Pass ID, replacement for typeid
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PPCLoopDataPrefetch() : FunctionPass(ID) {
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initializePPCLoopDataPrefetchPass(*PassRegistry::getPassRegistry());
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}
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addRequired<AssumptionCacheTracker>();
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AU.addPreserved<DominatorTreeWrapperPass>();
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AU.addRequired<LoopInfoWrapperPass>();
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AU.addPreserved<LoopInfoWrapperPass>();
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AU.addRequired<ScalarEvolution>();
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// FIXME: For some reason, preserving SE here breaks LSR (even if
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// this pass changes nothing).
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// AU.addPreserved<ScalarEvolution>();
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AU.addRequired<TargetTransformInfoWrapperPass>();
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}
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bool runOnFunction(Function &F) override;
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bool runOnLoop(Loop *L);
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private:
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AssumptionCache *AC;
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LoopInfo *LI;
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ScalarEvolution *SE;
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const TargetTransformInfo *TTI;
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const DataLayout *DL;
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};
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}
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char PPCLoopDataPrefetch::ID = 0;
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INITIALIZE_PASS_BEGIN(PPCLoopDataPrefetch, "ppc-loop-data-prefetch",
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"PPC Loop Data Prefetch", false, false)
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INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
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INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
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INITIALIZE_PASS_END(PPCLoopDataPrefetch, "ppc-loop-data-prefetch",
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"PPC Loop Data Prefetch", false, false)
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FunctionPass *llvm::createPPCLoopDataPrefetchPass() { return new PPCLoopDataPrefetch(); }
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bool PPCLoopDataPrefetch::runOnFunction(Function &F) {
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LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
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SE = &getAnalysis<ScalarEvolution>();
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DL = &F.getParent()->getDataLayout();
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AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
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TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
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bool MadeChange = false;
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for (auto I = LI->begin(), IE = LI->end(); I != IE; ++I)
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for (auto L = df_begin(*I), LE = df_end(*I); L != LE; ++L)
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MadeChange |= runOnLoop(*L);
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return MadeChange;
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}
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bool PPCLoopDataPrefetch::runOnLoop(Loop *L) {
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bool MadeChange = false;
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// Only prefetch in the inner-most loop
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if (!L->empty())
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return MadeChange;
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SmallPtrSet<const Value *, 32> EphValues;
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CodeMetrics::collectEphemeralValues(L, AC, EphValues);
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// Calculate the number of iterations ahead to prefetch
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CodeMetrics Metrics;
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for (Loop::block_iterator I = L->block_begin(), IE = L->block_end();
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I != IE; ++I) {
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// If the loop already has prefetches, then assume that the user knows
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// what he or she is doing and don't add any more.
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for (BasicBlock::iterator J = (*I)->begin(), JE = (*I)->end();
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J != JE; ++J)
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if (CallInst *CI = dyn_cast<CallInst>(J))
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if (Function *F = CI->getCalledFunction())
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if (F->getIntrinsicID() == Intrinsic::prefetch)
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return MadeChange;
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Metrics.analyzeBasicBlock(*I, *TTI, EphValues);
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}
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unsigned LoopSize = Metrics.NumInsts;
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if (!LoopSize)
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LoopSize = 1;
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unsigned ItersAhead = PrefDist/LoopSize;
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if (!ItersAhead)
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ItersAhead = 1;
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SmallVector<std::pair<Instruction *, const SCEVAddRecExpr *>, 16> PrefLoads;
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for (Loop::block_iterator I = L->block_begin(), IE = L->block_end();
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I != IE; ++I) {
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for (BasicBlock::iterator J = (*I)->begin(), JE = (*I)->end();
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J != JE; ++J) {
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Value *PtrValue;
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Instruction *MemI;
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if (LoadInst *LMemI = dyn_cast<LoadInst>(J)) {
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MemI = LMemI;
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PtrValue = LMemI->getPointerOperand();
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} else if (StoreInst *SMemI = dyn_cast<StoreInst>(J)) {
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if (!PrefetchWrites) continue;
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MemI = SMemI;
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PtrValue = SMemI->getPointerOperand();
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} else continue;
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unsigned PtrAddrSpace = PtrValue->getType()->getPointerAddressSpace();
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if (PtrAddrSpace)
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continue;
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if (L->isLoopInvariant(PtrValue))
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continue;
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const SCEV *LSCEV = SE->getSCEV(PtrValue);
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const SCEVAddRecExpr *LSCEVAddRec = dyn_cast<SCEVAddRecExpr>(LSCEV);
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if (!LSCEVAddRec)
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continue;
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// We don't want to double prefetch individual cache lines. If this load
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// is known to be within one cache line of some other load that has
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// already been prefetched, then don't prefetch this one as well.
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bool DupPref = false;
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for (SmallVector<std::pair<Instruction *, const SCEVAddRecExpr *>,
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16>::iterator K = PrefLoads.begin(), KE = PrefLoads.end();
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K != KE; ++K) {
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const SCEV *PtrDiff = SE->getMinusSCEV(LSCEVAddRec, K->second);
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if (const SCEVConstant *ConstPtrDiff =
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dyn_cast<SCEVConstant>(PtrDiff)) {
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int64_t PD = std::abs(ConstPtrDiff->getValue()->getSExtValue());
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if (PD < (int64_t) CacheLineSize) {
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DupPref = true;
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break;
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}
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}
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}
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if (DupPref)
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continue;
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const SCEV *NextLSCEV = SE->getAddExpr(LSCEVAddRec, SE->getMulExpr(
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SE->getConstant(LSCEVAddRec->getType(), ItersAhead),
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LSCEVAddRec->getStepRecurrence(*SE)));
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if (!isSafeToExpand(NextLSCEV, *SE))
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continue;
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PrefLoads.push_back(std::make_pair(MemI, LSCEVAddRec));
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Type *I8Ptr = Type::getInt8PtrTy((*I)->getContext(), PtrAddrSpace);
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SCEVExpander SCEVE(*SE, J->getModule()->getDataLayout(), "prefaddr");
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Value *PrefPtrValue = SCEVE.expandCodeFor(NextLSCEV, I8Ptr, MemI);
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IRBuilder<> Builder(MemI);
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Module *M = (*I)->getParent()->getParent();
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Type *I32 = Type::getInt32Ty((*I)->getContext());
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Value *PrefetchFunc = Intrinsic::getDeclaration(M, Intrinsic::prefetch);
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Builder.CreateCall4(PrefetchFunc, PrefPtrValue,
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ConstantInt::get(I32, MemI->mayReadFromMemory() ? 0 : 1),
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ConstantInt::get(I32, 3), ConstantInt::get(I32, 1));
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MadeChange = true;
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}
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}
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return MadeChange;
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}
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