//
// The LLVM Compiler Infrastructure
//
-// This file was developed by Devang Patel and is distributed under
-// the University of Illinois Open Source License. See LICENSE.TXT for details.
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Support/Compiler.h"
+#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
AU.addRequiredID(LoopSimplifyID);
AU.addPreservedID(LoopSimplifyID);
AU.addRequired<DominatorTree>();
+ AU.addRequired<DominanceFrontier>();
AU.addPreserved<DominatorTree>();
AU.addPreserved<DominanceFrontier>();
}
class SplitInfo {
public:
- SplitInfo() : SplitValue(NULL), SplitCondition(NULL) {}
+ SplitInfo() : SplitValue(NULL), SplitCondition(NULL),
+ UseTrueBranchFirst(true), A_ExitValue(NULL),
+ B_StartValue(NULL) {}
// Induction variable's range is split at this value.
Value *SplitValue;
- // This compare instruction compares IndVar against SplitValue.
- ICmpInst *SplitCondition;
+ // This instruction compares IndVar against SplitValue.
+ Instruction *SplitCondition;
+
+ // True if after loop index split, first loop will execute split condition's
+ // true branch.
+ bool UseTrueBranchFirst;
+
+ // Exit value for first loop after loop split.
+ Value *A_ExitValue;
+
+ // Start value for second loop after loop split.
+ Value *B_StartValue;
// Clear split info.
void clear() {
SplitValue = NULL;
SplitCondition = NULL;
+ UseTrueBranchFirst = true;
+ A_ExitValue = NULL;
+ B_StartValue = NULL;
}
};
private:
+
+ // safeIcmpInst - CI is considered safe instruction if one of the operand
+ // is SCEVAddRecExpr based on induction variable and other operand is
+ // loop invariant. If CI is safe then populate SplitInfo object SD appropriately
+ // and return true;
+ bool safeICmpInst(ICmpInst *CI, SplitInfo &SD);
+
/// Find condition inside a loop that is suitable candidate for index split.
void findSplitCondition();
/// instruction then loop body is executed only for one iteration. In
/// such case eliminate loop structure surrounding this loop body. For
bool processOneIterationLoop(SplitInfo &SD);
-
+
+ void updateLoopBounds(ICmpInst *CI);
+ /// updateLoopIterationSpace - Current loop body is covered by an AND
+ /// instruction whose operands compares induction variables with loop
+ /// invariants. If possible, hoist this check outside the loop by
+ /// updating appropriate start and end values for induction variable.
+ bool updateLoopIterationSpace(SplitInfo &SD);
+
/// If loop header includes loop variant instruction operands then
/// this loop may not be eliminated.
bool safeHeader(SplitInfo &SD, BasicBlock *BB);
- /// If Exit block includes loop variant instructions then this
+ /// If Exiting block includes loop variant instructions then this
/// loop may not be eliminated.
- bool safeExitBlock(SplitInfo &SD, BasicBlock *BB);
+ bool safeExitingBlock(SplitInfo &SD, BasicBlock *BB);
/// removeBlocks - Remove basic block DeadBB and all blocks dominated by DeadBB.
/// This routine is used to remove split condition's dead branch, dominated by
/// DeadBB. LiveBB dominates split conidition's other branch.
void removeBlocks(BasicBlock *DeadBB, Loop *LP, BasicBlock *LiveBB);
- /// Find cost of spliting loop L.
- unsigned findSplitCost(Loop *L, SplitInfo &SD);
+ /// safeSplitCondition - Return true if it is possible to
+ /// split loop using given split condition.
+ bool safeSplitCondition(SplitInfo &SD);
+
+ /// calculateLoopBounds - ALoop exit value and BLoop start values are calculated
+ /// based on split value.
+ void calculateLoopBounds(SplitInfo &SD);
+
+ /// updatePHINodes - CFG has been changed.
+ /// Before
+ /// - ExitBB's single predecessor was Latch
+ /// - Latch's second successor was Header
+ /// Now
+ /// - ExitBB's single predecessor was Header
+ /// - Latch's one and only successor was Header
+ ///
+ /// Update ExitBB PHINodes' to reflect this change.
+ void updatePHINodes(BasicBlock *ExitBB, BasicBlock *Latch,
+ BasicBlock *Header,
+ PHINode *IV, Instruction *IVIncrement, Loop *LP);
+
+ /// moveExitCondition - Move exit condition EC into split condition block CondBB.
+ void moveExitCondition(BasicBlock *CondBB, BasicBlock *ActiveBB,
+ BasicBlock *ExitBB, ICmpInst *EC, ICmpInst *SC,
+ PHINode *IV, Instruction *IVAdd, Loop *LP);
+
+ /// splitLoop - Split current loop L in two loops using split information
+ /// SD. Update dominator information. Maintain LCSSA form.
bool splitLoop(SplitInfo &SD);
void initialize() {
// Induction variable's final loop exit value operand number in exit condition..
unsigned ExitValueNum;
};
-
- char LoopIndexSplit::ID = 0;
- RegisterPass<LoopIndexSplit> X ("loop-index-split", "Index Split Loops");
}
+char LoopIndexSplit::ID = 0;
+static RegisterPass<LoopIndexSplit>
+X("loop-index-split", "Index Split Loops");
+
LoopPass *llvm::createLoopIndexSplitPass() {
return new LoopIndexSplit();
}
SE = &getAnalysis<ScalarEvolution>();
DT = &getAnalysis<DominatorTree>();
LI = &getAnalysis<LoopInfo>();
- DF = getAnalysisToUpdate<DominanceFrontier>();
+ DF = &getAnalysis<DominanceFrontier>();
initialize();
return false;
// First see if it is possible to eliminate loop itself or not.
- for (SmallVector<SplitInfo, 4>::iterator SI = SplitData.begin(),
- E = SplitData.end(); SI != E; ++SI) {
+ for (SmallVector<SplitInfo, 4>::iterator SI = SplitData.begin();
+ SI != SplitData.end();) {
SplitInfo &SD = *SI;
- if (SD.SplitCondition->getPredicate() == ICmpInst::ICMP_EQ) {
- Changed = processOneIterationLoop(SD);
+ ICmpInst *CI = dyn_cast<ICmpInst>(SD.SplitCondition);
+ if (SD.SplitCondition->getOpcode() == Instruction::And) {
+ Changed = updateLoopIterationSpace(SD);
if (Changed) {
++NumIndexSplit;
// If is loop is eliminated then nothing else to do here.
return Changed;
+ } else {
+ SmallVector<SplitInfo, 4>::iterator Delete_SI = SI;
+ SI = SplitData.erase(Delete_SI);
}
}
+ else if (CI && CI->getPredicate() == ICmpInst::ICMP_EQ) {
+ Changed = processOneIterationLoop(SD);
+ if (Changed) {
+ ++NumIndexSplit;
+ // If is loop is eliminated then nothing else to do here.
+ return Changed;
+ } else {
+ SmallVector<SplitInfo, 4>::iterator Delete_SI = SI;
+ SI = SplitData.erase(Delete_SI);
+ }
+ } else
+ ++SI;
}
- unsigned MaxCost = 99;
- unsigned Index = 0;
- unsigned MostProfitableSDIndex = 0;
- for (SmallVector<SplitInfo, 4>::iterator SI = SplitData.begin(),
- E = SplitData.end(); SI != E; ++SI, ++Index) {
- SplitInfo SD = *SI;
-
- // ICM_EQs are already handled above.
- if (SD.SplitCondition->getPredicate() == ICmpInst::ICMP_EQ)
- continue;
-
- unsigned Cost = findSplitCost(L, SD);
- if (Cost < MaxCost)
- MostProfitableSDIndex = Index;
- }
+ if (SplitData.empty())
+ return false;
// Split most profitiable condition.
+ // FIXME : Implement cost analysis.
+ unsigned MostProfitableSDIndex = 0;
Changed = splitLoop(SplitData[MostProfitableSDIndex]);
if (Changed)
Value *Op0 = I->getOperand(0);
Value *Op1 = I->getOperand(1);
- if (PHINode *PN = dyn_cast<PHINode>(Op0)) {
- if (PN->getParent() == L->getHeader()
- && isa<ConstantInt>(Op1)) {
- IndVar = PN;
- IndVarIncrement = I;
- return;
- }
- }
-
- if (PHINode *PN = dyn_cast<PHINode>(Op1)) {
- if (PN->getParent() == L->getHeader()
- && isa<ConstantInt>(Op0)) {
- IndVar = PN;
- IndVarIncrement = I;
- return;
- }
- }
+ if (PHINode *PN = dyn_cast<PHINode>(Op0))
+ if (PN->getParent() == L->getHeader())
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1))
+ if (CI->isOne()) {
+ IndVar = PN;
+ IndVarIncrement = I;
+ return;
+ }
+
+ if (PHINode *PN = dyn_cast<PHINode>(Op1))
+ if (PN->getParent() == L->getHeader())
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(Op0))
+ if (CI->isOne()) {
+ IndVar = PN;
+ IndVarIncrement = I;
+ return;
+ }
return;
}
// Find loop's exit condition and associated induction variable.
void LoopIndexSplit::findLoopConditionals() {
- BasicBlock *ExitBlock = NULL;
+ BasicBlock *ExitingBlock = NULL;
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
I != E; ++I) {
BasicBlock *BB = *I;
if (!L->isLoopExit(BB))
continue;
- if (ExitBlock)
+ if (ExitingBlock)
return;
- ExitBlock = BB;
+ ExitingBlock = BB;
}
- if (!ExitBlock)
+ if (!ExitingBlock)
return;
-
+
+ // If exiting block is neither loop header nor loop latch then this loop is
+ // not suitable.
+ if (ExitingBlock != L->getHeader() && ExitingBlock != L->getLoopLatch())
+ return;
+
// If exit block's terminator is conditional branch inst then we have found
// exit condition.
- BranchInst *BR = dyn_cast<BranchInst>(ExitBlock->getTerminator());
+ BranchInst *BR = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
if (!BR || BR->isUnconditional())
return;
ICmpInst *CI = dyn_cast<ICmpInst>(BR->getCondition());
if (!CI)
return;
-
+
+ // FIXME
+ if (CI->getPredicate() == ICmpInst::ICMP_EQ
+ || CI->getPredicate() == ICmpInst::ICMP_NE)
+ return;
+
ExitCondition = CI;
// Exit condition's one operand is loop invariant exit value and second
SplitInfo SD;
// Check all basic block's terminators.
-
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
I != E; ++I) {
+ SD.clear();
BasicBlock *BB = *I;
// If this basic block does not terminate in a conditional branch
if (BR->isUnconditional())
continue;
+ if (Instruction *AndI = dyn_cast<Instruction>(BR->getCondition())) {
+ if (AndI->getOpcode() == Instruction::And) {
+ ICmpInst *Op0 = dyn_cast<ICmpInst>(AndI->getOperand(0));
+ ICmpInst *Op1 = dyn_cast<ICmpInst>(AndI->getOperand(1));
+
+ if (!Op0 || !Op1)
+ continue;
+
+ if (!safeICmpInst(Op0, SD))
+ continue;
+ SD.clear();
+ if (!safeICmpInst(Op1, SD))
+ continue;
+ SD.clear();
+ SD.SplitCondition = AndI;
+ SplitData.push_back(SD);
+ continue;
+ }
+ }
ICmpInst *CI = dyn_cast<ICmpInst>(BR->getCondition());
if (!CI || CI == ExitCondition)
- return;
+ continue;
+
+ if (CI->getPredicate() == ICmpInst::ICMP_NE)
+ continue;
+
+ // If split condition predicate is GT or GE then first execute
+ // false branch of split condition.
+ if (CI->getPredicate() == ICmpInst::ICMP_UGT
+ || CI->getPredicate() == ICmpInst::ICMP_SGT
+ || CI->getPredicate() == ICmpInst::ICMP_UGE
+ || CI->getPredicate() == ICmpInst::ICMP_SGE)
+ SD.UseTrueBranchFirst = false;
// If one operand is loop invariant and second operand is SCEVAddRecExpr
// based on induction variable then CI is a candidate split condition.
- Value *V0 = CI->getOperand(0);
- Value *V1 = CI->getOperand(1);
-
- SCEVHandle SH0 = SE->getSCEV(V0);
- SCEVHandle SH1 = SE->getSCEV(V1);
-
- if (SH0->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH1)) {
- SD.SplitValue = V0;
- SD.SplitCondition = CI;
- if (PHINode *PN = dyn_cast<PHINode>(V1)) {
- if (PN == IndVar)
- SplitData.push_back(SD);
- }
- else if (Instruction *Insn = dyn_cast<Instruction>(V1)) {
- if (IndVarIncrement && IndVarIncrement == Insn)
- SplitData.push_back(SD);
- }
+ if (safeICmpInst(CI, SD))
+ SplitData.push_back(SD);
+ }
+}
+
+// safeIcmpInst - CI is considered safe instruction if one of the operand
+// is SCEVAddRecExpr based on induction variable and other operand is
+// loop invariant. If CI is safe then populate SplitInfo object SD appropriately
+// and return true;
+bool LoopIndexSplit::safeICmpInst(ICmpInst *CI, SplitInfo &SD) {
+
+ Value *V0 = CI->getOperand(0);
+ Value *V1 = CI->getOperand(1);
+
+ SCEVHandle SH0 = SE->getSCEV(V0);
+ SCEVHandle SH1 = SE->getSCEV(V1);
+
+ if (SH0->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH1)) {
+ SD.SplitValue = V0;
+ SD.SplitCondition = CI;
+ if (PHINode *PN = dyn_cast<PHINode>(V1)) {
+ if (PN == IndVar)
+ return true;
}
- else if (SH1->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH0)) {
- SD.SplitValue = V1;
- SD.SplitCondition = CI;
- if (PHINode *PN = dyn_cast<PHINode>(V0)) {
- if (PN == IndVar)
- SplitData.push_back(SD);
- }
- else if (Instruction *Insn = dyn_cast<Instruction>(V0)) {
- if (IndVarIncrement && IndVarIncrement == Insn)
- SplitData.push_back(SD);
- }
+ else if (Instruction *Insn = dyn_cast<Instruction>(V1)) {
+ if (IndVarIncrement && IndVarIncrement == Insn)
+ return true;
+ }
+ }
+ else if (SH1->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH0)) {
+ SD.SplitValue = V1;
+ SD.SplitCondition = CI;
+ if (PHINode *PN = dyn_cast<PHINode>(V0)) {
+ if (PN == IndVar)
+ return true;
+ }
+ else if (Instruction *Insn = dyn_cast<Instruction>(V0)) {
+ if (IndVarIncrement && IndVarIncrement == Insn)
+ return true;
}
}
+
+ return false;
}
/// processOneIterationLoop - Current loop L contains compare instruction
if (!safeHeader(SD, Header))
return false;
- // If Exit block includes loop variant instructions then this
+ // If Exiting block includes loop variant instructions then this
// loop may not be eliminated.
- if (!safeExitBlock(SD, ExitCondition->getParent()))
+ if (!safeExitingBlock(SD, ExitCondition->getParent()))
return false;
- // Update CFG.
+ // Filter loops where split condition's false branch is not empty.
+ if (ExitCondition->getParent() != Header->getTerminator()->getSuccessor(1))
+ return false;
+
+ // If split condition is not safe then do not process this loop.
+ // For example,
+ // for(int i = 0; i < N; i++) {
+ // if ( i == XYZ) {
+ // A;
+ // else
+ // B;
+ // }
+ // C;
+ // D;
+ // }
+ if (!safeSplitCondition(SD))
+ return false;
- // As a first step to break this loop, remove Latch to Header edge.
BasicBlock *Latch = L->getLoopLatch();
- BasicBlock *LatchSucc = NULL;
BranchInst *BR = dyn_cast<BranchInst>(Latch->getTerminator());
if (!BR)
return false;
+
+ // Update CFG.
+
+ // Replace index variable with split value in loop body. Loop body is executed
+ // only when index variable is equal to split value.
+ IndVar->replaceAllUsesWith(SD.SplitValue);
+
+ // Remove Latch to Header edge.
+ BasicBlock *LatchSucc = NULL;
Header->removePredecessor(Latch);
for (succ_iterator SI = succ_begin(Latch), E = succ_end(Latch);
SI != E; ++SI) {
// SplitCondition : icmp eq i32 IndVar, SplitValue
// into
// c1 = icmp uge i32 SplitValue, StartValue
- // c2 = icmp ult i32 vSplitValue, ExitValue
+ // c2 = icmp ult i32 SplitValue, ExitValue
// and i32 c1, c2
bool SignedPredicate = ExitCondition->isSignedPredicate();
Instruction *C1 = new ICmpInst(SignedPredicate ?
ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
SD.SplitValue, ExitValue, "lisplit",
Terminator);
- Instruction *NSplitCond = BinaryOperator::createAnd(C1, C2, "lisplit",
+ Instruction *NSplitCond = BinaryOperator::CreateAnd(C1, C2, "lisplit",
Terminator);
SD.SplitCondition->replaceAllUsesWith(NSplitCond);
SD.SplitCondition->eraseFromParent();
if (isa<PHINode>(I) || I == LTerminator)
continue;
- if (I == IndVarIncrement)
- I->replaceAllUsesWith(ExitValue);
- else
+ if (I == IndVarIncrement) {
+ // Replace induction variable increment if it is not used outside
+ // the loop.
+ bool UsedOutsideLoop = false;
+ for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
+ UI != E; ++UI) {
+ if (Instruction *Use = dyn_cast<Instruction>(UI))
+ if (!L->contains(Use->getParent())) {
+ UsedOutsideLoop = true;
+ break;
+ }
+ }
+ if (!UsedOutsideLoop) {
+ I->replaceAllUsesWith(ExitValue);
+ I->eraseFromParent();
+ }
+ }
+ else {
I->replaceAllUsesWith(UndefValue::get(I->getType()));
- I->eraseFromParent();
+ I->eraseFromParent();
+ }
}
LPM->deleteLoopFromQueue(L);
return true;
}
-// If Exit block includes loop variant instructions then this
+// If Exiting block includes loop variant instructions then this
// loop may not be eliminated. This is used by processOneIterationLoop().
-bool LoopIndexSplit::safeExitBlock(SplitInfo &SD, BasicBlock *ExitBlock) {
+bool LoopIndexSplit::safeExitingBlock(SplitInfo &SD,
+ BasicBlock *ExitingBlock) {
- for (BasicBlock::iterator BI = ExitBlock->begin(), BE = ExitBlock->end();
- BI != BE; ++BI) {
+ for (BasicBlock::iterator BI = ExitingBlock->begin(),
+ BE = ExitingBlock->end(); BI != BE; ++BI) {
Instruction *I = BI;
// PHI Nodes are OK.
continue;
// Check if I is induction variable increment instruction.
- if (!IndVarIncrement && I->getOpcode() == Instruction::Add) {
+ if (I->getOpcode() == Instruction::Add) {
Value *Op0 = I->getOperand(0);
Value *Op1 = I->getOperand(1);
if ((PN = dyn_cast<PHINode>(Op0))) {
if ((CI = dyn_cast<ConstantInt>(Op1)))
- IndVarIncrement = I;
+ if (CI->isOne()) {
+ if (!IndVarIncrement && PN == IndVar)
+ IndVarIncrement = I;
+ // else this is another loop induction variable
+ continue;
+ }
} else
if ((PN = dyn_cast<PHINode>(Op1))) {
if ((CI = dyn_cast<ConstantInt>(Op0)))
- IndVarIncrement = I;
+ if (CI->isOne()) {
+ if (!IndVarIncrement && PN == IndVar)
+ IndVarIncrement = I;
+ // else this is another loop induction variable
+ continue;
+ }
}
-
- if (IndVarIncrement && PN == IndVar && CI->isOne())
- continue;
- }
+ }
// I is an Exit condition if next instruction is block terminator.
// Exit condition is OK if it compares loop invariant exit value,
continue;
}
- if (I == ExitBlock->getTerminator())
+ if (I == ExitingBlock->getTerminator())
continue;
// Otherwise we have instruction that may not be safe.
return false;
}
- // We could not find any reason to consider ExitBlock unsafe.
+ // We could not find any reason to consider ExitingBlock unsafe.
return true;
}
-/// Find cost of spliting loop L. Cost is measured in terms of size growth.
-/// Size is growth is calculated based on amount of code duplicated in second
-/// loop.
-unsigned LoopIndexSplit::findSplitCost(Loop *L, SplitInfo &SD) {
+void LoopIndexSplit::updateLoopBounds(ICmpInst *CI) {
+
+ Value *V0 = CI->getOperand(0);
+ Value *V1 = CI->getOperand(1);
+ Value *NV = NULL;
+
+ SCEVHandle SH0 = SE->getSCEV(V0);
+
+ if (SH0->isLoopInvariant(L))
+ NV = V0;
+ else
+ NV = V1;
+
+ if (ExitCondition->getPredicate() == ICmpInst::ICMP_SGT
+ || ExitCondition->getPredicate() == ICmpInst::ICMP_UGT
+ || ExitCondition->getPredicate() == ICmpInst::ICMP_SGE
+ || ExitCondition->getPredicate() == ICmpInst::ICMP_UGE) {
+ ExitCondition->swapOperands();
+ if (ExitValueNum)
+ ExitValueNum = 0;
+ else
+ ExitValueNum = 1;
+ }
+
+ Value *NUB = NULL;
+ Value *NLB = NULL;
+ Value *UB = ExitCondition->getOperand(ExitValueNum);
+ const Type *Ty = NV->getType();
+ bool Sign = ExitCondition->isSignedPredicate();
+ BasicBlock *Preheader = L->getLoopPreheader();
+ Instruction *PHTerminator = Preheader->getTerminator();
+
+ assert (NV && "Unexpected value");
+
+ switch (CI->getPredicate()) {
+ case ICmpInst::ICMP_ULE:
+ case ICmpInst::ICMP_SLE:
+ // for (i = LB; i < UB; ++i)
+ // if (i <= NV && ...)
+ // LOOP_BODY
+ //
+ // is transformed into
+ // NUB = min (NV+1, UB)
+ // for (i = LB; i < NUB ; ++i)
+ // LOOP_BODY
+ //
+ if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLT
+ || ExitCondition->getPredicate() == ICmpInst::ICMP_ULT) {
+ Value *A = BinaryOperator::CreateAdd(NV, ConstantInt::get(Ty, 1, Sign),
+ "lsplit.add", PHTerminator);
+ Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
+ A, UB,"lsplit,c", PHTerminator);
+ NUB = SelectInst::Create(C, A, UB, "lsplit.nub", PHTerminator);
+ }
+
+ // for (i = LB; i <= UB; ++i)
+ // if (i <= NV && ...)
+ // LOOP_BODY
+ //
+ // is transformed into
+ // NUB = min (NV, UB)
+ // for (i = LB; i <= NUB ; ++i)
+ // LOOP_BODY
+ //
+ else if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLE
+ || ExitCondition->getPredicate() == ICmpInst::ICMP_ULE) {
+ Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
+ NV, UB, "lsplit.c", PHTerminator);
+ NUB = SelectInst::Create(C, NV, UB, "lsplit.nub", PHTerminator);
+ }
+ break;
+ case ICmpInst::ICMP_ULT:
+ case ICmpInst::ICMP_SLT:
+ // for (i = LB; i < UB; ++i)
+ // if (i < NV && ...)
+ // LOOP_BODY
+ //
+ // is transformed into
+ // NUB = min (NV, UB)
+ // for (i = LB; i < NUB ; ++i)
+ // LOOP_BODY
+ //
+ if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLT
+ || ExitCondition->getPredicate() == ICmpInst::ICMP_ULT) {
+ Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
+ NV, UB, "lsplit.c", PHTerminator);
+ NUB = SelectInst::Create(C, NV, UB, "lsplit.nub", PHTerminator);
+ }
+
+ // for (i = LB; i <= UB; ++i)
+ // if (i < NV && ...)
+ // LOOP_BODY
+ //
+ // is transformed into
+ // NUB = min (NV -1 , UB)
+ // for (i = LB; i <= NUB ; ++i)
+ // LOOP_BODY
+ //
+ else if (ExitCondition->getPredicate() == ICmpInst::ICMP_SLE
+ || ExitCondition->getPredicate() == ICmpInst::ICMP_ULE) {
+ Value *S = BinaryOperator::CreateSub(NV, ConstantInt::get(Ty, 1, Sign),
+ "lsplit.add", PHTerminator);
+ Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
+ S, UB, "lsplit.c", PHTerminator);
+ NUB = SelectInst::Create(C, S, UB, "lsplit.nub", PHTerminator);
+ }
+ break;
+ case ICmpInst::ICMP_UGE:
+ case ICmpInst::ICMP_SGE:
+ // for (i = LB; i (< or <=) UB; ++i)
+ // if (i >= NV && ...)
+ // LOOP_BODY
+ //
+ // is transformed into
+ // NLB = max (NV, LB)
+ // for (i = NLB; i (< or <=) UB ; ++i)
+ // LOOP_BODY
+ //
+ {
+ Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
+ NV, StartValue, "lsplit.c", PHTerminator);
+ NLB = SelectInst::Create(C, StartValue, NV, "lsplit.nlb", PHTerminator);
+ }
+ break;
+ case ICmpInst::ICMP_UGT:
+ case ICmpInst::ICMP_SGT:
+ // for (i = LB; i (< or <=) UB; ++i)
+ // if (i > NV && ...)
+ // LOOP_BODY
+ //
+ // is transformed into
+ // NLB = max (NV+1, LB)
+ // for (i = NLB; i (< or <=) UB ; ++i)
+ // LOOP_BODY
+ //
+ {
+ Value *A = BinaryOperator::CreateAdd(NV, ConstantInt::get(Ty, 1, Sign),
+ "lsplit.add", PHTerminator);
+ Value *C = new ICmpInst(Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
+ A, StartValue, "lsplit.c", PHTerminator);
+ NLB = SelectInst::Create(C, StartValue, A, "lsplit.nlb", PHTerminator);
+ }
+ break;
+ default:
+ assert ( 0 && "Unexpected split condition predicate");
+ }
+
+ if (NLB) {
+ unsigned i = IndVar->getBasicBlockIndex(Preheader);
+ IndVar->setIncomingValue(i, NLB);
+ }
+
+ if (NUB) {
+ ExitCondition->setOperand(ExitValueNum, NUB);
+ }
+}
+/// updateLoopIterationSpace - Current loop body is covered by an AND
+/// instruction whose operands compares induction variables with loop
+/// invariants. If possible, hoist this check outside the loop by
+/// updating appropriate start and end values for induction variable.
+bool LoopIndexSplit::updateLoopIterationSpace(SplitInfo &SD) {
+ BasicBlock *Header = L->getHeader();
+ BasicBlock *ExitingBlock = ExitCondition->getParent();
+ BasicBlock *SplitCondBlock = SD.SplitCondition->getParent();
+
+ ICmpInst *Op0 = cast<ICmpInst>(SD.SplitCondition->getOperand(0));
+ ICmpInst *Op1 = cast<ICmpInst>(SD.SplitCondition->getOperand(1));
+
+ if (Op0->getPredicate() == ICmpInst::ICMP_EQ
+ || Op0->getPredicate() == ICmpInst::ICMP_NE
+ || Op0->getPredicate() == ICmpInst::ICMP_EQ
+ || Op0->getPredicate() == ICmpInst::ICMP_NE)
+ return false;
+
+ // Check if SplitCondition dominates entire loop body
+ // or not.
+
+ // If SplitCondition is not in loop header then this loop is not suitable
+ // for this transformation.
+ if (SD.SplitCondition->getParent() != Header)
+ return false;
+
+ // If loop header includes loop variant instruction operands then
+ // this loop may not be eliminated.
+ Instruction *Terminator = Header->getTerminator();
+ for(BasicBlock::iterator BI = Header->begin(), BE = Header->end();
+ BI != BE; ++BI) {
+ Instruction *I = BI;
+
+ // PHI Nodes are OK.
+ if (isa<PHINode>(I))
+ continue;
+
+ // SplitCondition itself is OK.
+ if (I == SD.SplitCondition)
+ continue;
+ if (I == Op0 || I == Op1)
+ continue;
+
+ // Induction variable is OK.
+ if (I == IndVar)
+ continue;
- unsigned Cost = 0;
- BasicBlock *SDBlock = SD.SplitCondition->getParent();
+ // Induction variable increment is OK.
+ if (I == IndVarIncrement)
+ continue;
+
+ // Terminator is also harmless.
+ if (I == Terminator)
+ continue;
+
+ // Otherwise we have a instruction that may not be safe.
+ return false;
+ }
+
+ // If Exiting block includes loop variant instructions then this
+ // loop may not be eliminated.
+ if (!safeExitingBlock(SD, ExitCondition->getParent()))
+ return false;
+
+ // Verify that loop exiting block has only two predecessor, where one predecessor
+ // is split condition block. The other predecessor will become exiting block's
+ // dominator after CFG is updated. TODO : Handle CFG's where exiting block has
+ // more then two predecessors. This requires extra work in updating dominator
+ // information.
+ BasicBlock *ExitingBBPred = NULL;
+ for (pred_iterator PI = pred_begin(ExitingBlock), PE = pred_end(ExitingBlock);
+ PI != PE; ++PI) {
+ BasicBlock *BB = *PI;
+ if (SplitCondBlock == BB)
+ continue;
+ if (ExitingBBPred)
+ return false;
+ else
+ ExitingBBPred = BB;
+ }
+
+ // Update loop bounds to absorb Op0 check.
+ updateLoopBounds(Op0);
+ // Update loop bounds to absorb Op1 check.
+ updateLoopBounds(Op1);
+
+ // Update CFG
+
+ // Unconditionally connect split block to its remaining successor.
+ BranchInst *SplitTerminator =
+ cast<BranchInst>(SplitCondBlock->getTerminator());
+ BasicBlock *Succ0 = SplitTerminator->getSuccessor(0);
+ BasicBlock *Succ1 = SplitTerminator->getSuccessor(1);
+ if (Succ0 == ExitCondition->getParent())
+ SplitTerminator->setUnconditionalDest(Succ1);
+ else
+ SplitTerminator->setUnconditionalDest(Succ0);
+
+ // Remove split condition.
+ SD.SplitCondition->eraseFromParent();
+ if (Op0->use_begin() == Op0->use_end())
+ Op0->eraseFromParent();
+ if (Op1->use_begin() == Op1->use_end())
+ Op1->eraseFromParent();
+
+ BranchInst *ExitInsn =
+ dyn_cast<BranchInst>(ExitingBlock->getTerminator());
+ assert (ExitInsn && "Unable to find suitable loop exit branch");
+ BasicBlock *ExitBlock = ExitInsn->getSuccessor(1);
+ if (L->contains(ExitBlock))
+ ExitBlock = ExitInsn->getSuccessor(0);
+
+ // Update domiantor info. Now, ExitingBlock has only one predecessor,
+ // ExitingBBPred, and it is ExitingBlock's immediate domiantor.
+ DT->changeImmediateDominator(ExitingBlock, ExitingBBPred);
+
+ // If ExitingBlock is a member of loop BB's DF list then replace it with
+ // loop header and exit block.
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
I != E; ++I) {
BasicBlock *BB = *I;
- // If a block is not dominated by split condition block then
- // it must be duplicated in both loops.
- if (!DT->dominates(SDBlock, BB))
- Cost += BB->size();
+ if (BB == Header || BB == ExitingBlock)
+ continue;
+ DominanceFrontier::iterator BBDF = DF->find(BB);
+ DominanceFrontier::DomSetType::iterator DomSetI = BBDF->second.begin();
+ DominanceFrontier::DomSetType::iterator DomSetE = BBDF->second.end();
+ while (DomSetI != DomSetE) {
+ DominanceFrontier::DomSetType::iterator CurrentItr = DomSetI;
+ ++DomSetI;
+ BasicBlock *DFBB = *CurrentItr;
+ if (DFBB == ExitingBlock) {
+ BBDF->second.erase(DFBB);
+ BBDF->second.insert(Header);
+ if (Header != ExitingBlock)
+ BBDF->second.insert(ExitBlock);
+ }
+ }
}
- return Cost;
+ return true;
}
+
/// removeBlocks - Remove basic block DeadBB and all blocks dominated by DeadBB.
/// This routine is used to remove split condition's dead branch, dominated by
/// DeadBB. LiveBB dominates split conidition's other branch.
void LoopIndexSplit::removeBlocks(BasicBlock *DeadBB, Loop *LP,
BasicBlock *LiveBB) {
- SmallVector<std::pair<BasicBlock *, succ_iterator>, 8> WorkList;
- WorkList.push_back(std::make_pair(DeadBB, succ_begin(DeadBB)));
- while (!WorkList.empty()) {
- BasicBlock *BB = WorkList.back(). first;
- succ_iterator SIter = WorkList.back().second;
-
- // If all successor's are processed then remove this block.
- if (SIter == succ_end(BB)) {
- WorkList.pop_back();
- for(BasicBlock::iterator BBI = BB->begin(), BBE = BB->end();
- BBI != BBE; ++BBI) {
- Instruction *I = BBI;
- I->replaceAllUsesWith(UndefValue::get(I->getType()));
- I->eraseFromParent();
+ // First update DeadBB's dominance frontier.
+ SmallVector<BasicBlock *, 8> FrontierBBs;
+ DominanceFrontier::iterator DeadBBDF = DF->find(DeadBB);
+ if (DeadBBDF != DF->end()) {
+ SmallVector<BasicBlock *, 8> PredBlocks;
+
+ DominanceFrontier::DomSetType DeadBBSet = DeadBBDF->second;
+ for (DominanceFrontier::DomSetType::iterator DeadBBSetI = DeadBBSet.begin(),
+ DeadBBSetE = DeadBBSet.end(); DeadBBSetI != DeadBBSetE; ++DeadBBSetI) {
+ BasicBlock *FrontierBB = *DeadBBSetI;
+ FrontierBBs.push_back(FrontierBB);
+
+ // Rremove any PHI incoming edge from blocks dominated by DeadBB.
+ PredBlocks.clear();
+ for(pred_iterator PI = pred_begin(FrontierBB), PE = pred_end(FrontierBB);
+ PI != PE; ++PI) {
+ BasicBlock *P = *PI;
+ if (P == DeadBB || DT->dominates(DeadBB, P))
+ PredBlocks.push_back(P);
}
- LPM->deleteSimpleAnalysisValue(BB, LP);
- DT->eraseNode(BB);
- DF->removeBlock(BB);
- LI->removeBlock(BB);
- BB->eraseFromParent();
- } else {
- BasicBlock *SuccBB = *SIter;
- ++WorkList.back().second;
-
- if (DT->dominates(BB, SuccBB)) {
- WorkList.push_back(std::make_pair(SuccBB, succ_begin(SuccBB)));
- continue;
- } else {
- // If SuccBB is not dominated by BB then it is not removed, however remove
- // any PHI incoming edge from BB.
- for(BasicBlock::iterator SBI = SuccBB->begin(), SBE = SuccBB->end();
- SBI != SBE; ++SBI) {
- if (PHINode *PN = dyn_cast<PHINode>(SBI))
- PN->removeIncomingValue(BB);
- else
+
+ for(BasicBlock::iterator FBI = FrontierBB->begin(), FBE = FrontierBB->end();
+ FBI != FBE; ++FBI) {
+ if (PHINode *PN = dyn_cast<PHINode>(FBI)) {
+ for(SmallVector<BasicBlock *, 8>::iterator PI = PredBlocks.begin(),
+ PE = PredBlocks.end(); PI != PE; ++PI) {
+ BasicBlock *P = *PI;
+ PN->removeIncomingValue(P);
+ }
+ }
+ else
+ break;
+ }
+ }
+ }
+
+ // Now remove DeadBB and all nodes dominated by DeadBB in df order.
+ SmallVector<BasicBlock *, 32> WorkList;
+ DomTreeNode *DN = DT->getNode(DeadBB);
+ for (df_iterator<DomTreeNode*> DI = df_begin(DN),
+ E = df_end(DN); DI != E; ++DI) {
+ BasicBlock *BB = DI->getBlock();
+ WorkList.push_back(BB);
+ BB->replaceAllUsesWith(UndefValue::get(Type::LabelTy));
+ }
+
+ while (!WorkList.empty()) {
+ BasicBlock *BB = WorkList.back(); WorkList.pop_back();
+ for(BasicBlock::iterator BBI = BB->begin(), BBE = BB->end();
+ BBI != BBE; ) {
+ Instruction *I = BBI;
+ ++BBI;
+ I->replaceAllUsesWith(UndefValue::get(I->getType()));
+ I->eraseFromParent();
+ }
+ LPM->deleteSimpleAnalysisValue(BB, LP);
+ DT->eraseNode(BB);
+ DF->removeBlock(BB);
+ LI->removeBlock(BB);
+ BB->eraseFromParent();
+ }
+
+ // Update Frontier BBs' dominator info.
+ while (!FrontierBBs.empty()) {
+ BasicBlock *FBB = FrontierBBs.back(); FrontierBBs.pop_back();
+ BasicBlock *NewDominator = FBB->getSinglePredecessor();
+ if (!NewDominator) {
+ pred_iterator PI = pred_begin(FBB), PE = pred_end(FBB);
+ NewDominator = *PI;
+ ++PI;
+ if (NewDominator != LiveBB) {
+ for(; PI != PE; ++PI) {
+ BasicBlock *P = *PI;
+ if (P == LiveBB) {
+ NewDominator = LiveBB;
break;
+ }
+ NewDominator = DT->findNearestCommonDominator(NewDominator, P);
}
+ }
+ }
+ assert (NewDominator && "Unable to fix dominator info.");
+ DT->changeImmediateDominator(FBB, NewDominator);
+ DF->changeImmediateDominator(FBB, NewDominator, DT);
+ }
+
+}
+
+/// safeSplitCondition - Return true if it is possible to
+/// split loop using given split condition.
+bool LoopIndexSplit::safeSplitCondition(SplitInfo &SD) {
+
+ BasicBlock *SplitCondBlock = SD.SplitCondition->getParent();
+ BasicBlock *Latch = L->getLoopLatch();
+ BranchInst *SplitTerminator =
+ cast<BranchInst>(SplitCondBlock->getTerminator());
+ BasicBlock *Succ0 = SplitTerminator->getSuccessor(0);
+ BasicBlock *Succ1 = SplitTerminator->getSuccessor(1);
+
+ // If split block does not dominate the latch then this is not a diamond.
+ // Such loop may not benefit from index split.
+ if (!DT->dominates(SplitCondBlock, Latch))
+ return false;
+
+ // Finally this split condition is safe only if merge point for
+ // split condition branch is loop latch. This check along with previous
+ // check, to ensure that exit condition is in either loop latch or header,
+ // filters all loops with non-empty loop body between merge point
+ // and exit condition.
+ DominanceFrontier::iterator Succ0DF = DF->find(Succ0);
+ assert (Succ0DF != DF->end() && "Unable to find Succ0 dominance frontier");
+ if (Succ0DF->second.count(Latch))
+ return true;
+
+ DominanceFrontier::iterator Succ1DF = DF->find(Succ1);
+ assert (Succ1DF != DF->end() && "Unable to find Succ1 dominance frontier");
+ if (Succ1DF->second.count(Latch))
+ return true;
+
+ return false;
+}
+
+/// calculateLoopBounds - ALoop exit value and BLoop start values are calculated
+/// based on split value.
+void LoopIndexSplit::calculateLoopBounds(SplitInfo &SD) {
- DT->changeImmediateDominator(SuccBB, LiveBB);
-
- // If BB is not dominating SuccBB then SuccBB is in BB's dominance
- // frontiner.
- DominanceFrontier::iterator BBDF = DF->find(BB);
- DF->removeFromFrontier(BBDF, SuccBB);
-
- // LiveBB is now dominating SuccBB. Which means SuccBB's dominance
- // frontier is member of LiveBB's dominance frontier. However, SuccBB
- // itself is not member of LiveBB's dominance frontier.
- DominanceFrontier::iterator LiveDF = DF->find(LiveBB);
- DominanceFrontier::iterator SuccDF = DF->find(SuccBB);
- DominanceFrontier::DomSetType SuccBBSet = SuccDF->second;
- for (DominanceFrontier::DomSetType::iterator SuccBBSetI = SuccBBSet.begin(),
- SuccBBSetE = SuccBBSet.end(); SuccBBSetI != SuccBBSetE; ++SuccBBSetI) {
- BasicBlock *DFMember = *SuccBBSetI;
- // Insert only if LiveBB dominates DFMember.
- if (!DT->dominates(LiveBB, DFMember))
- LiveDF->second.insert(DFMember);
+ ICmpInst *SC = cast<ICmpInst>(SD.SplitCondition);
+ ICmpInst::Predicate SP = SC->getPredicate();
+ const Type *Ty = SD.SplitValue->getType();
+ bool Sign = ExitCondition->isSignedPredicate();
+ BasicBlock *Preheader = L->getLoopPreheader();
+ Instruction *PHTerminator = Preheader->getTerminator();
+
+ // Initially use split value as upper loop bound for first loop and lower loop
+ // bound for second loop.
+ Value *AEV = SD.SplitValue;
+ Value *BSV = SD.SplitValue;
+
+ if (ExitCondition->getPredicate() == ICmpInst::ICMP_SGT
+ || ExitCondition->getPredicate() == ICmpInst::ICMP_UGT
+ || ExitCondition->getPredicate() == ICmpInst::ICMP_SGE
+ || ExitCondition->getPredicate() == ICmpInst::ICMP_UGE) {
+ ExitCondition->swapOperands();
+ if (ExitValueNum)
+ ExitValueNum = 0;
+ else
+ ExitValueNum = 1;
+ }
+
+ switch (ExitCondition->getPredicate()) {
+ case ICmpInst::ICMP_SGT:
+ case ICmpInst::ICMP_UGT:
+ case ICmpInst::ICMP_SGE:
+ case ICmpInst::ICMP_UGE:
+ default:
+ assert (0 && "Unexpected exit condition predicate");
+
+ case ICmpInst::ICMP_SLT:
+ case ICmpInst::ICMP_ULT:
+ {
+ switch (SP) {
+ case ICmpInst::ICMP_SLT:
+ case ICmpInst::ICMP_ULT:
+ //
+ // for (i = LB; i < UB; ++i) { if (i < SV) A; else B; }
+ //
+ // is transformed into
+ // AEV = BSV = SV
+ // for (i = LB; i < min(UB, AEV); ++i)
+ // A;
+ // for (i = max(LB, BSV); i < UB; ++i);
+ // B;
+ break;
+ case ICmpInst::ICMP_SLE:
+ case ICmpInst::ICMP_ULE:
+ {
+ //
+ // for (i = LB; i < UB; ++i) { if (i <= SV) A; else B; }
+ //
+ // is transformed into
+ //
+ // AEV = SV + 1
+ // BSV = SV + 1
+ // for (i = LB; i < min(UB, AEV); ++i)
+ // A;
+ // for (i = max(LB, BSV); i < UB; ++i)
+ // B;
+ BSV = BinaryOperator::CreateAdd(SD.SplitValue,
+ ConstantInt::get(Ty, 1, Sign),
+ "lsplit.add", PHTerminator);
+ AEV = BSV;
}
+ break;
+ case ICmpInst::ICMP_SGE:
+ case ICmpInst::ICMP_UGE:
+ //
+ // for (i = LB; i < UB; ++i) { if (i >= SV) A; else B; }
+ //
+ // is transformed into
+ // AEV = BSV = SV
+ // for (i = LB; i < min(UB, AEV); ++i)
+ // B;
+ // for (i = max(BSV, LB); i < UB; ++i)
+ // A;
+ break;
+ case ICmpInst::ICMP_SGT:
+ case ICmpInst::ICMP_UGT:
+ {
+ //
+ // for (i = LB; i < UB; ++i) { if (i > SV) A; else B; }
+ //
+ // is transformed into
+ //
+ // BSV = AEV = SV + 1
+ // for (i = LB; i < min(UB, AEV); ++i)
+ // B;
+ // for (i = max(LB, BSV); i < UB; ++i)
+ // A;
+ BSV = BinaryOperator::CreateAdd(SD.SplitValue,
+ ConstantInt::get(Ty, 1, Sign),
+ "lsplit.add", PHTerminator);
+ AEV = BSV;
+ }
+ break;
+ default:
+ assert (0 && "Unexpected split condition predicate");
+ break;
+ } // end switch (SP)
+ }
+ break;
+ case ICmpInst::ICMP_SLE:
+ case ICmpInst::ICMP_ULE:
+ {
+ switch (SP) {
+ case ICmpInst::ICMP_SLT:
+ case ICmpInst::ICMP_ULT:
+ //
+ // for (i = LB; i <= UB; ++i) { if (i < SV) A; else B; }
+ //
+ // is transformed into
+ // AEV = SV - 1;
+ // BSV = SV;
+ // for (i = LB; i <= min(UB, AEV); ++i)
+ // A;
+ // for (i = max(LB, BSV); i <= UB; ++i)
+ // B;
+ AEV = BinaryOperator::CreateSub(SD.SplitValue,
+ ConstantInt::get(Ty, 1, Sign),
+ "lsplit.sub", PHTerminator);
+ break;
+ case ICmpInst::ICMP_SLE:
+ case ICmpInst::ICMP_ULE:
+ //
+ // for (i = LB; i <= UB; ++i) { if (i <= SV) A; else B; }
+ //
+ // is transformed into
+ // AEV = SV;
+ // BSV = SV + 1;
+ // for (i = LB; i <= min(UB, AEV); ++i)
+ // A;
+ // for (i = max(LB, BSV); i <= UB; ++i)
+ // B;
+ BSV = BinaryOperator::CreateAdd(SD.SplitValue,
+ ConstantInt::get(Ty, 1, Sign),
+ "lsplit.add", PHTerminator);
+ break;
+ case ICmpInst::ICMP_SGT:
+ case ICmpInst::ICMP_UGT:
+ //
+ // for (i = LB; i <= UB; ++i) { if (i > SV) A; else B; }
+ //
+ // is transformed into
+ // AEV = SV;
+ // BSV = SV + 1;
+ // for (i = LB; i <= min(AEV, UB); ++i)
+ // B;
+ // for (i = max(LB, BSV); i <= UB; ++i)
+ // A;
+ BSV = BinaryOperator::CreateAdd(SD.SplitValue,
+ ConstantInt::get(Ty, 1, Sign),
+ "lsplit.add", PHTerminator);
+ break;
+ case ICmpInst::ICMP_SGE:
+ case ICmpInst::ICMP_UGE:
+ // ** TODO **
+ //
+ // for (i = LB; i <= UB; ++i) { if (i >= SV) A; else B; }
+ //
+ // is transformed into
+ // AEV = SV - 1;
+ // BSV = SV;
+ // for (i = LB; i <= min(AEV, UB); ++i)
+ // B;
+ // for (i = max(LB, BSV); i <= UB; ++i)
+ // A;
+ AEV = BinaryOperator::CreateSub(SD.SplitValue,
+ ConstantInt::get(Ty, 1, Sign),
+ "lsplit.sub", PHTerminator);
+ break;
+ default:
+ assert (0 && "Unexpected split condition predicate");
+ break;
+ } // end switch (SP)
+ }
+ break;
+ }
- DF->removeFromFrontier(LiveDF, SuccBB);
+ // Calculate ALoop induction variable's new exiting value and
+ // BLoop induction variable's new starting value. Calculuate these
+ // values in original loop's preheader.
+ // A_ExitValue = min(SplitValue, OrignalLoopExitValue)
+ // B_StartValue = max(SplitValue, OriginalLoopStartValue)
+ Instruction *InsertPt = L->getHeader()->getFirstNonPHI();
+
+ // If ExitValue operand is also defined in Loop header then
+ // insert new ExitValue after this operand definition.
+ if (Instruction *EVN =
+ dyn_cast<Instruction>(ExitCondition->getOperand(ExitValueNum))) {
+ if (!isa<PHINode>(EVN))
+ if (InsertPt->getParent() == EVN->getParent()) {
+ BasicBlock::iterator LHBI = L->getHeader()->begin();
+ BasicBlock::iterator LHBE = L->getHeader()->end();
+ for(;LHBI != LHBE; ++LHBI) {
+ Instruction *I = LHBI;
+ if (I == EVN)
+ break;
+ }
+ InsertPt = ++LHBI;
}
- }
}
+ Value *C1 = new ICmpInst(Sign ?
+ ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
+ AEV,
+ ExitCondition->getOperand(ExitValueNum),
+ "lsplit.ev", InsertPt);
+
+ SD.A_ExitValue = SelectInst::Create(C1, AEV,
+ ExitCondition->getOperand(ExitValueNum),
+ "lsplit.ev", InsertPt);
+
+ Value *C2 = new ICmpInst(Sign ?
+ ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
+ BSV, StartValue, "lsplit.sv",
+ PHTerminator);
+ SD.B_StartValue = SelectInst::Create(C2, StartValue, BSV,
+ "lsplit.sv", PHTerminator);
}
+/// splitLoop - Split current loop L in two loops using split information
+/// SD. Update dominator information. Maintain LCSSA form.
bool LoopIndexSplit::splitLoop(SplitInfo &SD) {
- BasicBlock *Preheader = L->getLoopPreheader();
- BasicBlock *SplitBlock = SD.SplitCondition->getParent();
- BasicBlock *Latch = L->getLoopLatch();
- BasicBlock *Header = L->getHeader();
- BranchInst *SplitTerminator = cast<BranchInst>(SplitBlock->getTerminator());
+ if (!safeSplitCondition(SD))
+ return false;
- // FIXME - Unable to handle triange loops at the moment.
+ BasicBlock *SplitCondBlock = SD.SplitCondition->getParent();
+
+ // Unable to handle triange loops at the moment.
// In triangle loop, split condition is in header and one of the
// the split destination is loop latch. If split condition is EQ
// then such loops are already handle in processOneIterationLoop().
- if (Header == SplitBlock
- && (Latch == SplitTerminator->getSuccessor(0)
- || Latch == SplitTerminator->getSuccessor(1)))
+ BasicBlock *Latch = L->getLoopLatch();
+ BranchInst *SplitTerminator =
+ cast<BranchInst>(SplitCondBlock->getTerminator());
+ BasicBlock *Succ0 = SplitTerminator->getSuccessor(0);
+ BasicBlock *Succ1 = SplitTerminator->getSuccessor(1);
+ if (L->getHeader() == SplitCondBlock
+ && (Latch == Succ0 || Latch == Succ1))
return false;
- // True loop is original loop. False loop is cloned loop.
+ // If split condition branches heads do not have single predecessor,
+ // SplitCondBlock, then is not possible to remove inactive branch.
+ if (!Succ0->getSinglePredecessor() || !Succ1->getSinglePredecessor())
+ return false;
- bool SignedPredicate = ExitCondition->isSignedPredicate();
- //[*] Calculate True loop's new Exit Value in loop preheader.
- // TLExitValue = min(SplitValue, ExitValue)
- //[*] Calculate False loop's new Start Value in loop preheader.
- // FLStartValue = min(SplitValue, TrueLoop.StartValue)
- Value *TLExitValue = NULL;
- Value *FLStartValue = NULL;
- if (isa<ConstantInt>(SD.SplitValue)) {
- TLExitValue = SD.SplitValue;
- FLStartValue = SD.SplitValue;
- }
- else {
- Value *C1 = new ICmpInst(SignedPredicate ?
- ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
- SD.SplitValue,
- ExitCondition->getOperand(ExitValueNum),
- "lsplit.ev",
- Preheader->getTerminator());
- TLExitValue = new SelectInst(C1, SD.SplitValue,
- ExitCondition->getOperand(ExitValueNum),
- "lsplit.ev", Preheader->getTerminator());
-
- Value *C2 = new ICmpInst(SignedPredicate ?
- ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
- SD.SplitValue, StartValue, "lsplit.sv",
- Preheader->getTerminator());
- FLStartValue = new SelectInst(C2, SD.SplitValue, StartValue,
- "lsplit.sv", Preheader->getTerminator());
- }
-
- //[*] Clone loop. Avoid true destination of split condition and
- // the blocks dominated by true destination.
- DenseMap<const Value *, Value *> ValueMap;
- Loop *FalseLoop = CloneLoop(L, LPM, LI, ValueMap, this);
- BasicBlock *FalseHeader = FalseLoop->getHeader();
+ // If Exiting block includes loop variant instructions then this
+ // loop may not be split safely.
+ if (!safeExitingBlock(SD, ExitCondition->getParent()))
+ return false;
- //[*] True loop's exit edge enters False loop.
- PHINode *IndVarClone = cast<PHINode>(ValueMap[IndVar]);
- BasicBlock *ExitBlock = ExitCondition->getParent();
- BranchInst *ExitInsn = dyn_cast<BranchInst>(ExitBlock->getTerminator());
- assert (ExitInsn && "Unable to find suitable loop exit branch");
- BasicBlock *ExitDest = ExitInsn->getSuccessor(1);
+ // After loop is cloned there are two loops.
+ //
+ // First loop, referred as ALoop, executes first part of loop's iteration
+ // space split. Second loop, referred as BLoop, executes remaining
+ // part of loop's iteration space.
+ //
+ // ALoop's exit edge enters BLoop's header through a forwarding block which
+ // acts as a BLoop's preheader.
+ BasicBlock *Preheader = L->getLoopPreheader();
+
+ // Calculate ALoop induction variable's new exiting value and
+ // BLoop induction variable's new starting value.
+ calculateLoopBounds(SD);
- if (L->contains(ExitDest)) {
- ExitDest = ExitInsn->getSuccessor(0);
- ExitInsn->setSuccessor(0, FalseHeader);
+ //[*] Clone loop.
+ DenseMap<const Value *, Value *> ValueMap;
+ Loop *BLoop = CloneLoop(L, LPM, LI, ValueMap, this);
+ Loop *ALoop = L;
+ BasicBlock *B_Header = BLoop->getHeader();
+
+ //[*] ALoop's exiting edge BLoop's header.
+ // ALoop's original exit block becomes BLoop's exit block.
+ PHINode *B_IndVar = cast<PHINode>(ValueMap[IndVar]);
+ BasicBlock *A_ExitingBlock = ExitCondition->getParent();
+ BranchInst *A_ExitInsn =
+ dyn_cast<BranchInst>(A_ExitingBlock->getTerminator());
+ assert (A_ExitInsn && "Unable to find suitable loop exit branch");
+ BasicBlock *B_ExitBlock = A_ExitInsn->getSuccessor(1);
+ if (L->contains(B_ExitBlock)) {
+ B_ExitBlock = A_ExitInsn->getSuccessor(0);
+ A_ExitInsn->setSuccessor(0, B_Header);
} else
- ExitInsn->setSuccessor(1, FalseHeader);
+ A_ExitInsn->setSuccessor(1, B_Header);
+
+ //[*] Update ALoop's exit value using new exit value.
+ ExitCondition->setOperand(ExitValueNum, SD.A_ExitValue);
+
+ // [*] Update BLoop's header phi nodes. Remove incoming PHINode's from
+ // original loop's preheader. Add incoming PHINode values from
+ // ALoop's exiting block. Update BLoop header's domiantor info.
// Collect inverse map of Header PHINodes.
DenseMap<Value *, Value *> InverseMap;
break;
}
- // Update False loop's header
- for (BasicBlock::iterator BI = FalseHeader->begin(), BE = FalseHeader->end();
+ for (BasicBlock::iterator BI = B_Header->begin(), BE = B_Header->end();
BI != BE; ++BI) {
if (PHINode *PN = dyn_cast<PHINode>(BI)) {
+ // Remove incoming value from original preheader.
PN->removeIncomingValue(Preheader);
- if (PN == IndVarClone)
- PN->addIncoming(FLStartValue, ExitBlock);
+
+ // Add incoming value from A_ExitingBlock.
+ if (PN == B_IndVar)
+ PN->addIncoming(SD.B_StartValue, A_ExitingBlock);
else {
PHINode *OrigPN = cast<PHINode>(InverseMap[PN]);
- Value *V2 = OrigPN->getIncomingValueForBlock(ExitBlock);
- PN->addIncoming(V2, ExitBlock);
+ Value *V2 = NULL;
+ // If loop header is also loop exiting block then
+ // OrigPN is incoming value for B loop header.
+ if (A_ExitingBlock == L->getHeader())
+ V2 = OrigPN;
+ else
+ V2 = OrigPN->getIncomingValueForBlock(A_ExitingBlock);
+ PN->addIncoming(V2, A_ExitingBlock);
}
} else
break;
}
-
- // Update ExitDest. Now it's predecessor is False loop's exit block.
- BasicBlock *ExitBlockClone = cast<BasicBlock>(ValueMap[ExitBlock]);
- for (BasicBlock::iterator BI = ExitDest->begin(), BE = ExitDest->end();
+ DT->changeImmediateDominator(B_Header, A_ExitingBlock);
+ DF->changeImmediateDominator(B_Header, A_ExitingBlock, DT);
+
+ // [*] Update BLoop's exit block. Its new predecessor is BLoop's exit
+ // block. Remove incoming PHINode values from ALoop's exiting block.
+ // Add new incoming values from BLoop's incoming exiting value.
+ // Update BLoop exit block's dominator info..
+ BasicBlock *B_ExitingBlock = cast<BasicBlock>(ValueMap[A_ExitingBlock]);
+ for (BasicBlock::iterator BI = B_ExitBlock->begin(), BE = B_ExitBlock->end();
BI != BE; ++BI) {
if (PHINode *PN = dyn_cast<PHINode>(BI)) {
- PN->addIncoming(ValueMap[PN->getIncomingValueForBlock(ExitBlock)], ExitBlockClone);
- PN->removeIncomingValue(ExitBlock);
+ PN->addIncoming(ValueMap[PN->getIncomingValueForBlock(A_ExitingBlock)],
+ B_ExitingBlock);
+ PN->removeIncomingValue(A_ExitingBlock);
} else
break;
}
- if (DT) {
- DT->changeImmediateDominator(FalseHeader, ExitBlock);
- DT->changeImmediateDominator(ExitDest, cast<BasicBlock>(ValueMap[ExitBlock]));
+ DT->changeImmediateDominator(B_ExitBlock, B_ExitingBlock);
+ DF->changeImmediateDominator(B_ExitBlock, B_ExitingBlock, DT);
+
+ //[*] Split ALoop's exit edge. This creates a new block which
+ // serves two purposes. First one is to hold PHINode defnitions
+ // to ensure that ALoop's LCSSA form. Second use it to act
+ // as a preheader for BLoop.
+ BasicBlock *A_ExitBlock = SplitEdge(A_ExitingBlock, B_Header, this);
+
+ //[*] Preserve ALoop's LCSSA form. Create new forwarding PHINodes
+ // in A_ExitBlock to redefine outgoing PHI definitions from ALoop.
+ for(BasicBlock::iterator BI = B_Header->begin(), BE = B_Header->end();
+ BI != BE; ++BI) {
+ if (PHINode *PN = dyn_cast<PHINode>(BI)) {
+ Value *V1 = PN->getIncomingValueForBlock(A_ExitBlock);
+ PHINode *newPHI = PHINode::Create(PN->getType(), PN->getName());
+ newPHI->addIncoming(V1, A_ExitingBlock);
+ A_ExitBlock->getInstList().push_front(newPHI);
+ PN->removeIncomingValue(A_ExitBlock);
+ PN->addIncoming(newPHI, A_ExitBlock);
+ } else
+ break;
}
- assert (!L->contains(ExitDest) && " Unable to find exit edge destination");
+ //[*] Eliminate split condition's inactive branch from ALoop.
+ BasicBlock *A_SplitCondBlock = SD.SplitCondition->getParent();
+ BranchInst *A_BR = cast<BranchInst>(A_SplitCondBlock->getTerminator());
+ BasicBlock *A_InactiveBranch = NULL;
+ BasicBlock *A_ActiveBranch = NULL;
+ if (SD.UseTrueBranchFirst) {
+ A_ActiveBranch = A_BR->getSuccessor(0);
+ A_InactiveBranch = A_BR->getSuccessor(1);
+ } else {
+ A_ActiveBranch = A_BR->getSuccessor(1);
+ A_InactiveBranch = A_BR->getSuccessor(0);
+ }
+ A_BR->setUnconditionalDest(A_ActiveBranch);
+ removeBlocks(A_InactiveBranch, L, A_ActiveBranch);
+
+ //[*] Eliminate split condition's inactive branch in from BLoop.
+ BasicBlock *B_SplitCondBlock = cast<BasicBlock>(ValueMap[A_SplitCondBlock]);
+ BranchInst *B_BR = cast<BranchInst>(B_SplitCondBlock->getTerminator());
+ BasicBlock *B_InactiveBranch = NULL;
+ BasicBlock *B_ActiveBranch = NULL;
+ if (SD.UseTrueBranchFirst) {
+ B_ActiveBranch = B_BR->getSuccessor(1);
+ B_InactiveBranch = B_BR->getSuccessor(0);
+ } else {
+ B_ActiveBranch = B_BR->getSuccessor(0);
+ B_InactiveBranch = B_BR->getSuccessor(1);
+ }
+ B_BR->setUnconditionalDest(B_ActiveBranch);
+ removeBlocks(B_InactiveBranch, BLoop, B_ActiveBranch);
- //[*] Split Exit Edge.
- SplitEdge(ExitBlock, FalseHeader, this);
+ BasicBlock *A_Header = L->getHeader();
+ if (A_ExitingBlock == A_Header)
+ return true;
- //[*] Eliminate split condition's false branch from True loop.
- BranchInst *BR = cast<BranchInst>(SplitBlock->getTerminator());
- BasicBlock *FBB = BR->getSuccessor(1);
- BR->setUnconditionalDest(BR->getSuccessor(0));
- removeBlocks(FBB, L, BR->getSuccessor(0));
+ //[*] Move exit condition into split condition block to avoid
+ // executing dead loop iteration.
+ ICmpInst *B_ExitCondition = cast<ICmpInst>(ValueMap[ExitCondition]);
+ Instruction *B_IndVarIncrement = cast<Instruction>(ValueMap[IndVarIncrement]);
+ ICmpInst *B_SplitCondition = cast<ICmpInst>(ValueMap[SD.SplitCondition]);
- //[*] Update True loop's exit value using new exit value.
- ExitCondition->setOperand(ExitValueNum, TLExitValue);
+ moveExitCondition(A_SplitCondBlock, A_ActiveBranch, A_ExitBlock, ExitCondition,
+ cast<ICmpInst>(SD.SplitCondition), IndVar, IndVarIncrement,
+ ALoop);
- //[*] Eliminate split condition's true branch in False loop CFG.
- BasicBlock *FSplitBlock = cast<BasicBlock>(ValueMap[SplitBlock]);
- BranchInst *FBR = cast<BranchInst>(FSplitBlock->getTerminator());
- BasicBlock *TBB = FBR->getSuccessor(0);
- FBR->setUnconditionalDest(FBR->getSuccessor(1));
- removeBlocks(TBB, FalseLoop, cast<BasicBlock>(FBR->getSuccessor(0)));
+ moveExitCondition(B_SplitCondBlock, B_ActiveBranch, B_ExitBlock, B_ExitCondition,
+ B_SplitCondition, B_IndVar, B_IndVarIncrement, BLoop);
return true;
}
+// moveExitCondition - Move exit condition EC into split condition block CondBB.
+void LoopIndexSplit::moveExitCondition(BasicBlock *CondBB, BasicBlock *ActiveBB,
+ BasicBlock *ExitBB, ICmpInst *EC, ICmpInst *SC,
+ PHINode *IV, Instruction *IVAdd, Loop *LP) {
+
+ BasicBlock *ExitingBB = EC->getParent();
+ Instruction *CurrentBR = CondBB->getTerminator();
+
+ // Move exit condition into split condition block.
+ EC->moveBefore(CurrentBR);
+ EC->setOperand(ExitValueNum == 0 ? 1 : 0, IV);
+
+ // Move exiting block's branch into split condition block. Update its branch
+ // destination.
+ BranchInst *ExitingBR = cast<BranchInst>(ExitingBB->getTerminator());
+ ExitingBR->moveBefore(CurrentBR);
+ BasicBlock *OrigDestBB = NULL;
+ if (ExitingBR->getSuccessor(0) == ExitBB) {
+ OrigDestBB = ExitingBR->getSuccessor(1);
+ ExitingBR->setSuccessor(1, ActiveBB);
+ }
+ else {
+ OrigDestBB = ExitingBR->getSuccessor(0);
+ ExitingBR->setSuccessor(0, ActiveBB);
+ }
+
+ // Remove split condition and current split condition branch.
+ SC->eraseFromParent();
+ CurrentBR->eraseFromParent();
+
+ // Connect exiting block to original destination.
+ BranchInst::Create(OrigDestBB, ExitingBB);
+
+ // Update PHINodes
+ updatePHINodes(ExitBB, ExitingBB, CondBB, IV, IVAdd, LP);
+
+ // Fix dominator info.
+ // ExitBB is now dominated by CondBB
+ DT->changeImmediateDominator(ExitBB, CondBB);
+ DF->changeImmediateDominator(ExitBB, CondBB, DT);
+
+ // Basicblocks dominated by ActiveBB may have ExitingBB or
+ // a basic block outside the loop in their DF list. If so,
+ // replace it with CondBB.
+ DomTreeNode *Node = DT->getNode(ActiveBB);
+ for (df_iterator<DomTreeNode *> DI = df_begin(Node), DE = df_end(Node);
+ DI != DE; ++DI) {
+ BasicBlock *BB = DI->getBlock();
+ DominanceFrontier::iterator BBDF = DF->find(BB);
+ DominanceFrontier::DomSetType::iterator DomSetI = BBDF->second.begin();
+ DominanceFrontier::DomSetType::iterator DomSetE = BBDF->second.end();
+ while (DomSetI != DomSetE) {
+ DominanceFrontier::DomSetType::iterator CurrentItr = DomSetI;
+ ++DomSetI;
+ BasicBlock *DFBB = *CurrentItr;
+ if (DFBB == ExitingBB || !L->contains(DFBB)) {
+ BBDF->second.erase(DFBB);
+ BBDF->second.insert(CondBB);
+ }
+ }
+ }
+}
+
+/// updatePHINodes - CFG has been changed.
+/// Before
+/// - ExitBB's single predecessor was Latch
+/// - Latch's second successor was Header
+/// Now
+/// - ExitBB's single predecessor is Header
+/// - Latch's one and only successor is Header
+///
+/// Update ExitBB PHINodes' to reflect this change.
+void LoopIndexSplit::updatePHINodes(BasicBlock *ExitBB, BasicBlock *Latch,
+ BasicBlock *Header,
+ PHINode *IV, Instruction *IVIncrement,
+ Loop *LP) {
+
+ for (BasicBlock::iterator BI = ExitBB->begin(), BE = ExitBB->end();
+ BI != BE; ) {
+ PHINode *PN = dyn_cast<PHINode>(BI);
+ ++BI;
+ if (!PN)
+ break;
+
+ Value *V = PN->getIncomingValueForBlock(Latch);
+ if (PHINode *PHV = dyn_cast<PHINode>(V)) {
+ // PHV is in Latch. PHV has one use is in ExitBB PHINode. And one use
+ // in Header which is new incoming value for PN.
+ Value *NewV = NULL;
+ for (Value::use_iterator UI = PHV->use_begin(), E = PHV->use_end();
+ UI != E; ++UI)
+ if (PHINode *U = dyn_cast<PHINode>(*UI))
+ if (LP->contains(U->getParent())) {
+ NewV = U;
+ break;
+ }
+
+ // Add incoming value from header only if PN has any use inside the loop.
+ if (NewV)
+ PN->addIncoming(NewV, Header);
+
+ } else if (Instruction *PHI = dyn_cast<Instruction>(V)) {
+ // If this instruction is IVIncrement then IV is new incoming value
+ // from header otherwise this instruction must be incoming value from
+ // header because loop is in LCSSA form.
+ if (PHI == IVIncrement)
+ PN->addIncoming(IV, Header);
+ else
+ PN->addIncoming(V, Header);
+ } else
+ // Otherwise this is an incoming value from header because loop is in
+ // LCSSA form.
+ PN->addIncoming(V, Header);
+
+ // Remove incoming value from Latch.
+ PN->removeIncomingValue(Latch);
+ }
+}
projects / oota-llvm.git / blobdiff