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-rw-r--r--llvm/lib/Transforms/Scalar/LICM.cpp317
1 files changed, 15 insertions, 302 deletions
diff --git a/llvm/lib/Transforms/Scalar/LICM.cpp b/llvm/lib/Transforms/Scalar/LICM.cpp
index 9f6a34c9fb2..e30c25da6b4 100644
--- a/llvm/lib/Transforms/Scalar/LICM.cpp
+++ b/llvm/lib/Transforms/Scalar/LICM.cpp
@@ -31,7 +31,6 @@
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/LICM.h"
-#include "llvm/ADT/SetOperations.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AliasSetTracker.h"
@@ -42,7 +41,6 @@
#include "llvm/Analysis/GuardUtils.h"
#include "llvm/Analysis/Loads.h"
#include "llvm/Analysis/LoopInfo.h"
-#include "llvm/Analysis/LoopIterator.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/MemorySSA.h"
@@ -77,8 +75,6 @@ using namespace llvm;
#define DEBUG_TYPE "licm"
-STATISTIC(NumCreatedBlocks, "Number of blocks created");
-STATISTIC(NumClonedBranches, "Number of branches cloned");
STATISTIC(NumSunk, "Number of instructions sunk out of loop");
STATISTIC(NumHoisted, "Number of instructions hoisted out of loop");
STATISTIC(NumMovedLoads, "Number of load insts hoisted or sunk");
@@ -107,7 +103,7 @@ static bool isNotUsedOrFreeInLoop(const Instruction &I, const Loop *CurLoop,
const LoopSafetyInfo *SafetyInfo,
TargetTransformInfo *TTI, bool &FreeInLoop);
static void hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
- BasicBlock *Dest, ICFLoopSafetyInfo *SafetyInfo,
+ ICFLoopSafetyInfo *SafetyInfo,
OptimizationRemarkEmitter *ORE);
static bool sink(Instruction &I, LoopInfo *LI, DominatorTree *DT,
const Loop *CurLoop, ICFLoopSafetyInfo *SafetyInfo,
@@ -441,225 +437,6 @@ bool llvm::sinkRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
return Changed;
}
-// This is a helper class for hoistRegion to make it able to hoist control flow
-// in order to be able to hoist phis. The way this works is that we initially
-// start hoisting to the loop preheader, and when we see a loop invariant branch
-// we make note of this. When we then come to hoist an instruction that's
-// conditional on such a branch we duplicate the branch and the relevant control
-// flow, then hoist the instruction into the block corresponding to its original
-// block in the duplicated control flow.
-class ControlFlowHoister {
-private:
- // Information about the loop we are hoisting from
- LoopInfo *LI;
- DominatorTree *DT;
- Loop *CurLoop;
-
- // A map of blocks in the loop to the block their instructions will be hoisted
- // to.
- DenseMap<BasicBlock *, BasicBlock *> HoistDestinationMap;
-
- // The branches that we can hoist, mapped to the block that marks a
- // convergence point of their control flow.
- DenseMap<BranchInst *, BasicBlock *> HoistableBranches;
-
-public:
- ControlFlowHoister(LoopInfo *LI, DominatorTree *DT, Loop *CurLoop)
- : LI(LI), DT(DT), CurLoop(CurLoop) {}
-
- void registerPossiblyHoistableBranch(BranchInst *BI) {
- // We can only hoist conditional branches with loop invariant operands.
- if (!BI->isConditional() || !CurLoop->hasLoopInvariantOperands(BI))
- return;
-
- // The branch destinations need to be in the loop, and we don't gain
- // anything by duplicating conditional branches with duplicate successors,
- // as it's essentially the same as an unconditional branch.
- BasicBlock *TrueDest = BI->getSuccessor(0);
- BasicBlock *FalseDest = BI->getSuccessor(1);
- if (!CurLoop->contains(TrueDest) || !CurLoop->contains(FalseDest) ||
- TrueDest == FalseDest)
- return;
-
- // We can hoist BI if one branch destination is the successor of the other,
- // or both have common successor which we check by seeing if the
- // intersection of their successors is non-empty.
- // TODO: This could be expanded to allowing branches where both ends
- // eventually converge to a single block.
- SmallPtrSet<BasicBlock *, 4> TrueDestSucc, FalseDestSucc;
- TrueDestSucc.insert(succ_begin(TrueDest), succ_end(TrueDest));
- FalseDestSucc.insert(succ_begin(FalseDest), succ_end(FalseDest));
- BasicBlock *CommonSucc = nullptr;
- if (TrueDestSucc.count(FalseDest)) {
- CommonSucc = FalseDest;
- } else if (FalseDestSucc.count(TrueDest)) {
- CommonSucc = TrueDest;
- } else {
- set_intersect(TrueDestSucc, FalseDestSucc);
- // If there's one common successor use that.
- if (TrueDestSucc.size() == 1)
- CommonSucc = *TrueDestSucc.begin();
- // If there's more than one pick whichever appears first in the block list
- // (we can't use the value returned by TrueDestSucc.begin() as it's
- // unpredicatable which element gets returned).
- else if (!TrueDestSucc.empty()) {
- Function *F = TrueDest->getParent();
- auto IsSucc = [&](BasicBlock &BB) { return TrueDestSucc.count(&BB); };
- auto It = std::find_if(F->begin(), F->end(), IsSucc);
- assert(It != F->end() && "Could not find successor in function");
- CommonSucc = &*It;
- }
- }
- // The common successor has to be dominated by the branch, as otherwise
- // there will be some other path to the successor that will not be
- // controlled by this branch so any phi we hoist would be controlled by the
- // wrong condition. This also takes care of avoiding hoisting of loop back
- // edges.
- // TODO: In some cases this could be relaxed if the successor is dominated
- // by another block that's been hoisted and we can guarantee that the
- // control flow has been replicated exactly.
- if (CommonSucc && DT->dominates(BI, CommonSucc))
- HoistableBranches[BI] = CommonSucc;
- }
-
- bool canHoistPHI(PHINode *PN) {
- // The phi must have loop invariant operands.
- if (!CurLoop->hasLoopInvariantOperands(PN))
- return false;
- // We can hoist phis if the block they are in is the target of hoistable
- // branches which cover all of the predecessors of the block.
- SmallPtrSet<BasicBlock *, 8> PredecessorBlocks;
- BasicBlock *BB = PN->getParent();
- for (BasicBlock *PredBB : predecessors(BB))
- PredecessorBlocks.insert(PredBB);
- // If we have less predecessor blocks than predecessors then the phi will
- // have more than one incoming value for the same block which we can't
- // handle.
- // TODO: This could be handled be erasing some of the duplicate incoming
- // values.
- if (PredecessorBlocks.size() != pred_size(BB))
- return false;
- for (auto &Pair : HoistableBranches) {
- if (Pair.second == BB) {
- // Which blocks are predecessors via this branch depends on if the
- // branch is triangle-like or diamond-like.
- if (Pair.first->getSuccessor(0) == BB) {
- PredecessorBlocks.erase(Pair.first->getParent());
- PredecessorBlocks.erase(Pair.first->getSuccessor(1));
- } else if (Pair.first->getSuccessor(1) == BB) {
- PredecessorBlocks.erase(Pair.first->getParent());
- PredecessorBlocks.erase(Pair.first->getSuccessor(0));
- } else {
- PredecessorBlocks.erase(Pair.first->getSuccessor(0));
- PredecessorBlocks.erase(Pair.first->getSuccessor(1));
- }
- }
- }
- // PredecessorBlocks will now be empty if for every predecessor of BB we
- // found a hoistable branch source.
- return PredecessorBlocks.empty();
- }
-
- BasicBlock *getOrCreateHoistedBlock(BasicBlock *BB) {
- // If BB has already been hoisted, return that
- if (HoistDestinationMap.count(BB))
- return HoistDestinationMap[BB];
-
- // Check if this block is conditional based on a pending branch
- auto HasBBAsSuccessor =
- [&](DenseMap<BranchInst *, BasicBlock *>::value_type &Pair) {
- return BB != Pair.second && (Pair.first->getSuccessor(0) == BB ||
- Pair.first->getSuccessor(1) == BB);
- };
- auto It = std::find_if(HoistableBranches.begin(), HoistableBranches.end(),
- HasBBAsSuccessor);
-
- // If not involved in a pending branch, hoist to preheader
- BasicBlock *InitialPreheader = CurLoop->getLoopPreheader();
- if (It == HoistableBranches.end()) {
- LLVM_DEBUG(dbgs() << "LICM using " << InitialPreheader->getName()
- << " as hoist destination for " << BB->getName()
- << "\n");
- HoistDestinationMap[BB] = InitialPreheader;
- return InitialPreheader;
- }
- BranchInst *BI = It->first;
- assert(std::find_if(++It, HoistableBranches.end(), HasBBAsSuccessor) ==
- HoistableBranches.end() &&
- "BB is expected to be the target of at most one branch");
-
- LLVMContext &C = BB->getContext();
- BasicBlock *TrueDest = BI->getSuccessor(0);
- BasicBlock *FalseDest = BI->getSuccessor(1);
- BasicBlock *CommonSucc = HoistableBranches[BI];
- BasicBlock *HoistTarget = getOrCreateHoistedBlock(BI->getParent());
-
- // Create hoisted versions of blocks that currently don't have them
- auto CreateHoistedBlock = [&](BasicBlock *Orig) {
- if (HoistDestinationMap.count(Orig))
- return HoistDestinationMap[Orig];
- BasicBlock *New =
- BasicBlock::Create(C, Orig->getName() + ".licm", Orig->getParent());
- HoistDestinationMap[Orig] = New;
- DT->addNewBlock(New, HoistTarget);
- if (CurLoop->getParentLoop())
- CurLoop->getParentLoop()->addBasicBlockToLoop(New, *LI);
- ++NumCreatedBlocks;
- LLVM_DEBUG(dbgs() << "LICM created " << New->getName()
- << " as hoist destination for " << Orig->getName()
- << "\n");
- return New;
- };
- BasicBlock *HoistTrueDest = CreateHoistedBlock(TrueDest);
- BasicBlock *HoistFalseDest = CreateHoistedBlock(FalseDest);
- BasicBlock *HoistCommonSucc = CreateHoistedBlock(CommonSucc);
-
- // Link up these blocks with branches.
- if (!HoistCommonSucc->getTerminator()) {
- // The new common successor we've generated will branch to whatever that
- // hoist target branched to.
- BasicBlock *TargetSucc = HoistTarget->getSingleSuccessor();
- assert(TargetSucc && "Expected hoist target to have a single successor");
- HoistCommonSucc->moveBefore(TargetSucc);
- BranchInst::Create(TargetSucc, HoistCommonSucc);
- }
- if (!HoistTrueDest->getTerminator()) {
- HoistTrueDest->moveBefore(HoistCommonSucc);
- BranchInst::Create(HoistCommonSucc, HoistTrueDest);
- }
- if (!HoistFalseDest->getTerminator()) {
- HoistFalseDest->moveBefore(HoistCommonSucc);
- BranchInst::Create(HoistCommonSucc, HoistFalseDest);
- }
-
- // If BI is being cloned to what was originally the preheader then
- // HoistCommonSucc will now be the new preheader.
- if (HoistTarget == InitialPreheader) {
- // Phis in the loop header now need to use the new preheader.
- InitialPreheader->replaceSuccessorsPhiUsesWith(HoistCommonSucc);
- // The new preheader dominates the loop header.
- DomTreeNode *PreheaderNode = DT->getNode(HoistCommonSucc);
- DomTreeNode *HeaderNode = DT->getNode(CurLoop->getHeader());
- DT->changeImmediateDominator(HeaderNode, PreheaderNode);
- // The preheader hoist destination is now the new preheader, with the
- // exception of the hoist destination of this branch.
- for (auto &Pair : HoistDestinationMap)
- if (Pair.second == InitialPreheader && Pair.first != BI->getParent())
- Pair.second = HoistCommonSucc;
- }
-
- // Now finally clone BI.
- ReplaceInstWithInst(
- HoistTarget->getTerminator(),
- BranchInst::Create(HoistTrueDest, HoistFalseDest, BI->getCondition()));
- ++NumClonedBranches;
-
- assert(CurLoop->getLoopPreheader() &&
- "Hoisting blocks should not have destroyed preheader");
- return HoistDestinationMap[BB];
- }
-};
-
/// Walk the specified region of the CFG (defined by all blocks dominated by
/// the specified block, and that are in the current loop) in depth first
/// order w.r.t the DominatorTree. This allows us to visit definitions before
@@ -674,23 +451,13 @@ bool llvm::hoistRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
CurLoop != nullptr && CurAST != nullptr && SafetyInfo != nullptr &&
"Unexpected input to hoistRegion");
- ControlFlowHoister CFH(LI, DT, CurLoop);
-
- // Keep track of instructions that have been hoisted, as they may need to be
- // re-hoisted if they end up not dominating all of their uses.
- SmallVector<Instruction *, 16> HoistedInstructions;
-
- // Record what the original preheader is, as we'll need it later if we need to
- // re-hoist instructions.
- BasicBlock *OriginalPreheader = CurLoop->getLoopPreheader();
+ // We want to visit parents before children. We will enque all the parents
+ // before their children in the worklist and process the worklist in order.
+ SmallVector<DomTreeNode *, 16> Worklist = collectChildrenInLoop(N, CurLoop);
- // For PHI hoisting to work we need to hoist blocks before their successors.
- // We can do this by iterating through the blocks in the loop in reverse
- // post-order.
- LoopBlocksRPO Worklist(CurLoop);
- Worklist.perform(LI);
bool Changed = false;
- for (BasicBlock *BB : Worklist) {
+ for (DomTreeNode *DTN : Worklist) {
+ BasicBlock *BB = DTN->getBlock();
// Only need to process the contents of this block if it is not part of a
// subloop (which would already have been processed).
if (inSubLoop(BB, CurLoop, LI))
@@ -716,16 +483,13 @@ bool llvm::hoistRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
// Try hoisting the instruction out to the preheader. We can only do
// this if all of the operands of the instruction are loop invariant and
// if it is safe to hoist the instruction.
- // TODO: It may be safe to hoist if we are hoisting to a conditional block
- // and we have accurately duplicated the control flow from the loop header
- // to that block.
+ //
if (CurLoop->hasLoopInvariantOperands(&I) &&
canSinkOrHoistInst(I, AA, DT, CurLoop, CurAST, true, ORE) &&
isSafeToExecuteUnconditionally(
I, DT, CurLoop, SafetyInfo, ORE,
CurLoop->getLoopPreheader()->getTerminator())) {
- hoist(I, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB), SafetyInfo, ORE);
- HoistedInstructions.push_back(&I);
+ hoist(I, DT, CurLoop, SafetyInfo, ORE);
Changed = true;
continue;
}
@@ -750,9 +514,7 @@ bool llvm::hoistRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
I.replaceAllUsesWith(Product);
eraseInstruction(I, *SafetyInfo, CurAST);
- hoist(*ReciprocalDivisor, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB),
- SafetyInfo, ORE);
- HoistedInstructions.push_back(ReciprocalDivisor);
+ hoist(*ReciprocalDivisor, DT, CurLoop, SafetyInfo, ORE);
Changed = true;
continue;
}
@@ -764,58 +526,13 @@ bool llvm::hoistRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
CurLoop->hasLoopInvariantOperands(&I) &&
SafetyInfo->isGuaranteedToExecute(I, DT, CurLoop) &&
SafetyInfo->doesNotWriteMemoryBefore(I, CurLoop)) {
- hoist(I, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB), SafetyInfo, ORE);
- HoistedInstructions.push_back(&I);
+ hoist(I, DT, CurLoop, SafetyInfo, ORE);
Changed = true;
continue;
}
-
- if (PHINode *PN = dyn_cast<PHINode>(&I)) {
- if (CFH.canHoistPHI(PN)) {
- // Redirect incoming blocks first to ensure that we create hoisted
- // versions of those blocks before we hoist the phi.
- for (unsigned int i = 0; i < PN->getNumIncomingValues(); ++i)
- PN->setIncomingBlock(
- i, CFH.getOrCreateHoistedBlock(PN->getIncomingBlock(i)));
- hoist(*PN, DT, CurLoop, CFH.getOrCreateHoistedBlock(BB), SafetyInfo,
- ORE);
- assert(DT->dominates(PN, BB) && "Conditional PHIs not expected");
- Changed = true;
- continue;
- }
- }
-
- // Remember possibly hoistable branches so we can actually hoist them
- // later if needed.
- if (BranchInst *BI = dyn_cast<BranchInst>(&I))
- CFH.registerPossiblyHoistableBranch(BI);
}
}
- // If we hoisted instructions to a conditional block they may not dominate
- // their uses that weren't hoisted (such as phis where some operands are not
- // loop invariant). If so make them unconditional by moving them to the end of
- // the original preheader, which is guaranteed to dominate everything in the
- // loop. We iterate through the instructions in reverse order which ensures
- // that when we rehoist an instruction we rehoist its operands.
- Instruction *HoistPoint = OriginalPreheader->getTerminator();
- for (Instruction *I : reverse(HoistedInstructions)) {
- if (!llvm::all_of(I->uses(), [&](Use &U) { return DT->dominates(I, U); })) {
- LLVM_DEBUG(dbgs() << "LICM rehoisting to " << OriginalPreheader->getName()
- << ": " << *I << "\n");
- moveInstructionBefore(*I, *HoistPoint, *SafetyInfo);
- HoistPoint = I;
- Changed = true;
- }
- }
-
- // Now that we've finished hoisting make sure that LI and DT are still valid.
-#ifndef NDEBUG
- assert(DT->verify(DominatorTree::VerificationLevel::Fast) &&
- "Dominator tree verification failed");
- LI->verify(*DT);
-#endif
-
return Changed;
}
@@ -1383,9 +1100,9 @@ static bool sink(Instruction &I, LoopInfo *LI, DominatorTree *DT,
/// is safe to hoist, this instruction is called to do the dirty work.
///
static void hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
- BasicBlock *Dest, ICFLoopSafetyInfo *SafetyInfo,
- OptimizationRemarkEmitter *ORE) {
- LLVM_DEBUG(dbgs() << "LICM hoisting to " << Dest->getName() << ": " << I
+ ICFLoopSafetyInfo *SafetyInfo, OptimizationRemarkEmitter *ORE) {
+ auto *Preheader = CurLoop->getLoopPreheader();
+ LLVM_DEBUG(dbgs() << "LICM hoisting to " << Preheader->getName() << ": " << I
<< "\n");
ORE->emit([&]() {
return OptimizationRemark(DEBUG_TYPE, "Hoisted", &I) << "hoisting "
@@ -1403,12 +1120,8 @@ static void hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
!SafetyInfo->isGuaranteedToExecute(I, DT, CurLoop))
I.dropUnknownNonDebugMetadata();
- if (isa<PHINode>(I))
- // Move the new node to the end of the phi list in the destination block.
- moveInstructionBefore(I, *Dest->getFirstNonPHI(), *SafetyInfo);
- else
- // Move the new node to the destination block, before its terminator.
- moveInstructionBefore(I, *Dest->getTerminator(), *SafetyInfo);
+ // Move the new node to the Preheader, before its terminator.
+ moveInstructionBefore(I, *Preheader->getTerminator(), *SafetyInfo);
// Do not retain debug locations when we are moving instructions to different
// basic blocks, because we want to avoid jumpy line tables. Calls, however,
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