forked from OSchip/llvm-project
117 lines
4.8 KiB
C++
117 lines
4.8 KiB
C++
//===- LoopVersioning.cpp - Utility to version a loop ---------------------===//
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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 defines a utility class to perform loop versioning. The versioned
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// loop speculates that otherwise may-aliasing memory accesses don't overlap and
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// emits checks to prove this.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/LoopAccessAnalysis.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/Cloning.h"
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#include "llvm/Transforms/Utils/LoopVersioning.h"
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using namespace llvm;
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LoopVersioning::LoopVersioning(
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SmallVector<RuntimePointerChecking::PointerCheck, 4> Checks,
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const LoopAccessInfo &LAI, Loop *L, LoopInfo *LI, DominatorTree *DT)
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: VersionedLoop(L), NonVersionedLoop(nullptr), Checks(std::move(Checks)),
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LAI(LAI), LI(LI), DT(DT) {
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assert(L->getExitBlock() && "No single exit block");
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assert(L->getLoopPreheader() && "No preheader");
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}
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LoopVersioning::LoopVersioning(const LoopAccessInfo &LAInfo, Loop *L,
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LoopInfo *LI, DominatorTree *DT)
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: VersionedLoop(L), NonVersionedLoop(nullptr),
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Checks(LAInfo.getRuntimePointerChecking()->getChecks()), LAI(LAInfo),
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LI(LI), DT(DT) {
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assert(L->getExitBlock() && "No single exit block");
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assert(L->getLoopPreheader() && "No preheader");
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}
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void LoopVersioning::versionLoop(
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const SmallVectorImpl<Instruction *> &DefsUsedOutside) {
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Instruction *FirstCheckInst;
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Instruction *MemRuntimeCheck;
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// Add the memcheck in the original preheader (this is empty initially).
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BasicBlock *MemCheckBB = VersionedLoop->getLoopPreheader();
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std::tie(FirstCheckInst, MemRuntimeCheck) =
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LAI.addRuntimeChecks(MemCheckBB->getTerminator(), Checks);
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assert(MemRuntimeCheck && "called even though needsAnyChecking = false");
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// Rename the block to make the IR more readable.
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MemCheckBB->setName(VersionedLoop->getHeader()->getName() + ".lver.memcheck");
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// Create empty preheader for the loop (and after cloning for the
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// non-versioned loop).
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BasicBlock *PH = SplitBlock(MemCheckBB, MemCheckBB->getTerminator(), DT, LI);
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PH->setName(VersionedLoop->getHeader()->getName() + ".ph");
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// Clone the loop including the preheader.
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//
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// FIXME: This does not currently preserve SimplifyLoop because the exit
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// block is a join between the two loops.
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SmallVector<BasicBlock *, 8> NonVersionedLoopBlocks;
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NonVersionedLoop =
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cloneLoopWithPreheader(PH, MemCheckBB, VersionedLoop, VMap, ".lver.orig",
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LI, DT, NonVersionedLoopBlocks);
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remapInstructionsInBlocks(NonVersionedLoopBlocks, VMap);
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// Insert the conditional branch based on the result of the memchecks.
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Instruction *OrigTerm = MemCheckBB->getTerminator();
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BranchInst::Create(NonVersionedLoop->getLoopPreheader(),
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VersionedLoop->getLoopPreheader(), MemRuntimeCheck,
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OrigTerm);
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OrigTerm->eraseFromParent();
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// The loops merge in the original exit block. This is now dominated by the
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// memchecking block.
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DT->changeImmediateDominator(VersionedLoop->getExitBlock(), MemCheckBB);
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// Adds the necessary PHI nodes for the versioned loops based on the
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// loop-defined values used outside of the loop.
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addPHINodes(DefsUsedOutside);
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}
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void LoopVersioning::addPHINodes(
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const SmallVectorImpl<Instruction *> &DefsUsedOutside) {
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BasicBlock *PHIBlock = VersionedLoop->getExitBlock();
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assert(PHIBlock && "No single successor to loop exit block");
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for (auto *Inst : DefsUsedOutside) {
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auto *NonVersionedLoopInst = cast<Instruction>(VMap[Inst]);
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PHINode *PN;
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// First see if we have a single-operand PHI with the value defined by the
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// original loop.
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for (auto I = PHIBlock->begin(); (PN = dyn_cast<PHINode>(I)); ++I) {
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assert(PN->getNumOperands() == 1 &&
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"Exit block should only have on predecessor");
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if (PN->getIncomingValue(0) == Inst)
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break;
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}
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// If not create it.
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if (!PN) {
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PN = PHINode::Create(Inst->getType(), 2, Inst->getName() + ".lver",
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&PHIBlock->front());
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for (auto *User : Inst->users())
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if (!VersionedLoop->contains(cast<Instruction>(User)->getParent()))
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User->replaceUsesOfWith(Inst, PN);
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PN->addIncoming(Inst, VersionedLoop->getExitingBlock());
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}
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// Add the new incoming value from the non-versioned loop.
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PN->addIncoming(NonVersionedLoopInst, NonVersionedLoop->getExitingBlock());
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}
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}
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