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Diffstat (limited to 'llvm/lib/Transforms/Utils/LoopPeel.cpp')
-rw-r--r--llvm/lib/Transforms/Utils/LoopPeel.cpp82
1 files changed, 21 insertions, 61 deletions
diff --git a/llvm/lib/Transforms/Utils/LoopPeel.cpp b/llvm/lib/Transforms/Utils/LoopPeel.cpp
index 4d43c6a..f348d24 100644
--- a/llvm/lib/Transforms/Utils/LoopPeel.cpp
+++ b/llvm/lib/Transforms/Utils/LoopPeel.cpp
@@ -38,7 +38,6 @@
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Transforms/Utils/LoopSimplify.h"
#include "llvm/Transforms/Utils/LoopUtils.h"
-#include "llvm/Transforms/Utils/ScalarEvolutionExpander.h"
#include "llvm/Transforms/Utils/ValueMapper.h"
#include <algorithm>
#include <cassert>
@@ -331,7 +330,11 @@ static unsigned peelToTurnInvariantLoadsDerefencebale(Loop &L,
bool llvm::canPeelLastIteration(const Loop &L, ScalarEvolution &SE) {
const SCEV *BTC = SE.getBackedgeTakenCount(&L);
- if (isa<SCEVCouldNotCompute>(BTC))
+ // The loop must execute at least 2 iterations to guarantee that peeled
+ // iteration executes.
+ // TODO: Add checks during codegen.
+ if (isa<SCEVCouldNotCompute>(BTC) ||
+ !SE.isKnownPredicate(CmpInst::ICMP_UGT, BTC, SE.getZero(BTC->getType())))
return false;
// Check if the exit condition of the loop can be adjusted by the peeling
@@ -361,18 +364,12 @@ bool llvm::canPeelLastIteration(const Loop &L, ScalarEvolution &SE) {
/// is known at the second-to-last.
static bool shouldPeelLastIteration(Loop &L, CmpPredicate Pred,
const SCEVAddRecExpr *LeftAR,
- const SCEV *RightSCEV, ScalarEvolution &SE,
- const TargetTransformInfo &TTI) {
+ const SCEV *RightSCEV,
+ ScalarEvolution &SE) {
if (!canPeelLastIteration(L, SE))
return false;
const SCEV *BTC = SE.getBackedgeTakenCount(&L);
- SCEVExpander Expander(SE, L.getHeader()->getDataLayout(), "loop-peel");
- if (!SE.isKnownNonZero(BTC) &&
- Expander.isHighCostExpansion(BTC, &L, SCEVCheapExpansionBudget, &TTI,
- L.getLoopPredecessor()->getTerminator()))
- return false;
-
const SCEV *ValAtLastIter = LeftAR->evaluateAtIteration(BTC, SE);
const SCEV *ValAtSecondToLastIter = LeftAR->evaluateAtIteration(
SE.getMinusSCEV(BTC, SE.getOne(BTC->getType())), SE);
@@ -394,8 +391,7 @@ static bool shouldPeelLastIteration(Loop &L, CmpPredicate Pred,
// ..
// }
static std::pair<unsigned, unsigned>
-countToEliminateCompares(Loop &L, unsigned MaxPeelCount, ScalarEvolution &SE,
- const TargetTransformInfo &TTI) {
+countToEliminateCompares(Loop &L, unsigned MaxPeelCount, ScalarEvolution &SE) {
assert(L.isLoopSimplifyForm() && "Loop needs to be in loop simplify form");
unsigned DesiredPeelCount = 0;
unsigned DesiredPeelCountLast = 0;
@@ -483,7 +479,7 @@ countToEliminateCompares(Loop &L, unsigned MaxPeelCount, ScalarEvolution &SE,
const SCEV *Step = LeftAR->getStepRecurrence(SE);
if (!PeelWhilePredicateIsKnown(NewPeelCount, IterVal, RightSCEV, Step,
Pred)) {
- if (shouldPeelLastIteration(L, Pred, LeftAR, RightSCEV, SE, TTI))
+ if (shouldPeelLastIteration(L, Pred, LeftAR, RightSCEV, SE))
DesiredPeelCountLast = 1;
return;
}
@@ -597,8 +593,8 @@ static bool violatesLegacyMultiExitLoopCheck(Loop *L) {
void llvm::computePeelCount(Loop *L, unsigned LoopSize,
TargetTransformInfo::PeelingPreferences &PP,
unsigned TripCount, DominatorTree &DT,
- ScalarEvolution &SE, const TargetTransformInfo &TTI,
- AssumptionCache *AC, unsigned Threshold) {
+ ScalarEvolution &SE, AssumptionCache *AC,
+ unsigned Threshold) {
assert(LoopSize > 0 && "Zero loop size is not allowed!");
// Save the PP.PeelCount value set by the target in
// TTI.getPeelingPreferences or by the flag -unroll-peel-count.
@@ -660,7 +656,7 @@ void llvm::computePeelCount(Loop *L, unsigned LoopSize,
}
const auto &[CountToEliminateCmps, CountToEliminateCmpsLast] =
- countToEliminateCompares(*L, MaxPeelCount, SE, TTI);
+ countToEliminateCompares(*L, MaxPeelCount, SE);
DesiredPeelCount = std::max(DesiredPeelCount, CountToEliminateCmps);
if (DesiredPeelCount == 0)
@@ -826,7 +822,7 @@ static void initBranchWeights(DenseMap<Instruction *, WeightInfo> &WeightInfos,
/// instructions in the last peeled-off iteration.
static void cloneLoopBlocks(
Loop *L, unsigned IterNumber, bool PeelLast, BasicBlock *InsertTop,
- BasicBlock *InsertBot, BasicBlock *OrigPreHeader,
+ BasicBlock *InsertBot,
SmallVectorImpl<std::pair<BasicBlock *, BasicBlock *>> &ExitEdges,
SmallVectorImpl<BasicBlock *> &NewBlocks, LoopBlocksDFS &LoopBlocks,
ValueToValueMapTy &VMap, ValueToValueMapTy &LVMap, DominatorTree *DT,
@@ -918,22 +914,12 @@ static void cloneLoopBlocks(
// loop iteration. Since this copy is no longer part of the loop, we
// resolve this statically:
if (PeelLast) {
- // For the last iteration, we introduce new phis for each header phi in
- // InsertTop, using the incoming value from the preheader for the original
- // preheader (when skipping the main loop) and the incoming value from the
- // latch for the latch (when continuing from the main loop).
- IRBuilder<> B(InsertTop, InsertTop->getFirstNonPHIIt());
+ // For the last iteration, we use the value from the latch of the original
+ // loop directly.
for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
PHINode *NewPHI = cast<PHINode>(VMap[&*I]);
- PHINode *PN = B.CreatePHI(NewPHI->getType(), 2);
+ VMap[&*I] = NewPHI->getIncomingValueForBlock(Latch);
NewPHI->eraseFromParent();
- if (OrigPreHeader)
- PN->addIncoming(cast<PHINode>(&*I)->getIncomingValueForBlock(PreHeader),
- OrigPreHeader);
-
- PN->addIncoming(cast<PHINode>(&*I)->getIncomingValueForBlock(Latch),
- Latch);
- VMap[&*I] = PN;
}
} else {
// For the first iteration, we use the value from the preheader directly.
@@ -1067,7 +1053,7 @@ bool llvm::peelLoop(Loop *L, unsigned PeelCount, bool PeelLast, LoopInfo *LI,
// Set up all the necessary basic blocks.
BasicBlock *InsertTop;
BasicBlock *InsertBot;
- BasicBlock *NewPreHeader = nullptr;
+ BasicBlock *NewPreHeader;
DenseMap<Instruction *, Value *> ExitValues;
if (PeelLast) {
// It is convenient to split the single exit block from the latch the
@@ -1098,34 +1084,11 @@ bool llvm::peelLoop(Loop *L, unsigned PeelCount, bool PeelLast, LoopInfo *LI,
for (PHINode &P : Exit->phis())
ExitValues[&P] = P.getIncomingValueForBlock(Latch);
- const SCEV *BTC = SE->getBackedgeTakenCount(L);
-
InsertTop = SplitEdge(Latch, Exit, &DT, LI);
InsertBot = SplitBlock(InsertTop, InsertTop->getTerminator(), &DT, LI);
InsertTop->setName(Exit->getName() + ".peel.begin");
InsertBot->setName(Exit->getName() + ".peel.next");
- NewPreHeader = nullptr;
-
- // If the original loop may only execute a single iteration we need to
- // insert a trip count check and skip the original loop with the last
- // iteration peeled off if necessary.
- if (!SE->isKnownNonZero(BTC)) {
- NewPreHeader = SplitEdge(PreHeader, Header, &DT, LI);
- SCEVExpander Expander(*SE, Latch->getDataLayout(), "loop-peel");
-
- BranchInst *PreHeaderBR = cast<BranchInst>(PreHeader->getTerminator());
- Value *BTCValue =
- Expander.expandCodeFor(BTC, BTC->getType(), PreHeaderBR);
- IRBuilder<> B(PreHeaderBR);
- Value *Cond =
- B.CreateICmpNE(BTCValue, ConstantInt::get(BTCValue->getType(), 0));
- B.CreateCondBr(Cond, NewPreHeader, InsertTop);
- PreHeaderBR->eraseFromParent();
-
- // PreHeader now dominates InsertTop.
- DT.changeImmediateDominator(InsertTop, PreHeader);
- }
} else {
// It is convenient to split the preheader into 3 parts - two blocks to
// anchor the peeled copy of the loop body, and a new preheader for the
@@ -1199,9 +1162,8 @@ bool llvm::peelLoop(Loop *L, unsigned PeelCount, bool PeelLast, LoopInfo *LI,
for (unsigned Iter = 0; Iter < PeelCount; ++Iter) {
SmallVector<BasicBlock *, 8> NewBlocks;
- cloneLoopBlocks(L, Iter, PeelLast, InsertTop, InsertBot,
- NewPreHeader ? PreHeader : nullptr, ExitEdges, NewBlocks,
- LoopBlocks, VMap, LVMap, &DT, LI,
+ cloneLoopBlocks(L, Iter, PeelLast, InsertTop, InsertBot, ExitEdges,
+ NewBlocks, LoopBlocks, VMap, LVMap, &DT, LI,
LoopLocalNoAliasDeclScopes, *SE);
// Remap to use values from the current iteration instead of the
@@ -1254,11 +1216,9 @@ bool llvm::peelLoop(Loop *L, unsigned PeelCount, bool PeelLast, LoopInfo *LI,
if (PeelLast) {
// Now adjust users of the original exit values by replacing them with the
- // exit value from the peeled iteration and remove them.
- for (const auto &[P, E] : ExitValues) {
+ // exit value from the peeled iteration.
+ for (const auto &[P, E] : ExitValues)
P->replaceAllUsesWith(isa<Constant>(E) ? E : &*VMap.lookup(E));
- P->eraseFromParent();
- }
formLCSSA(*L, DT, LI, SE);
} else {
// Now adjust the phi nodes in the loop header to get their initial values
generated by cgit v1.1 at 2025-10-01 02:39:10 +0000