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ExitCondition and Induction variable are loop constraints

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not split condition constraints.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@40977 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Devang Patel 2007-08-10 00:33:50 +00:00
parent b31e91cb16
commit bacf5193cf
1 changed files with 145 additions and 71 deletions
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214
lib/Transforms/Scalar/LoopIndexSplit.cpp
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@ -53,46 +53,32 @@ namespace {
class SplitInfo {
public:
SplitInfo() : IndVar(NULL), SplitValue(NULL), ExitValue(NULL),
SplitCondition(NULL), ExitCondition(NULL),
IndVarIncrement(NULL) {}
// Induction variable whose range is being split by this transformation.
PHINode *IndVar;
SplitInfo() : SplitValue(NULL), SplitCondition(NULL) {}
// Induction variable's range is split at this value.
Value *SplitValue;
// Induction variable's final loop exit value.
Value *ExitValue;
// This compare instruction compares IndVar against SplitValue.
ICmpInst *SplitCondition;
// Loop exit condition.
ICmpInst *ExitCondition;
Instruction *IndVarIncrement;
// Clear split info.
void clear() {
IndVar = NULL;
SplitValue = NULL;
ExitValue = NULL;
SplitCondition = NULL;
ExitCondition = NULL;
IndVarIncrement = NULL;
}
/// Return true if V is a induction variable or induction variable's
/// increment for loop L.
bool findIndVar(Value *V, Loop *L);
};
private:
/// Find condition inside a loop that is suitable candidate for index split.
void findSplitCondition();
/// Find loop's exit condition.
void findLoopConditionals();
/// Return induction variable associated with value V.
void findIndVar(Value *V, Loop *L);
/// processOneIterationLoop - Current loop L contains compare instruction
/// that compares induction variable, IndVar, agains loop invariant. If
/// entire (i.e. meaningful) loop body is dominated by this compare
@ -112,6 +98,13 @@ namespace {
unsigned findSplitCost(Loop *L, SplitInfo &SD);
bool splitLoop(SplitInfo &SD);
void initialize() {
IndVar = NULL;
IndVarIncrement = NULL;
ExitCondition = NULL;
StartValue = ExitValue = NULL;
}
private:
// Current Loop.
@ -119,6 +112,19 @@ namespace {
ScalarEvolution *SE;
DominatorTree *DT;
SmallVector<SplitInfo, 4> SplitData;
// Induction variable whose range is being split by this transformation.
PHINode *IndVar;
Instruction *IndVarIncrement;
// Loop exit condition.
ICmpInst *ExitCondition;
// Induction variable's initial value.
Value *StartValue;
// Induction variable's final loop exit value.
Value *ExitValue;
};
char LoopIndexSplit::ID = 0;
@ -137,6 +143,13 @@ bool LoopIndexSplit::runOnLoop(Loop *IncomingLoop, LPPassManager &LPM) {
SE = &getAnalysis<ScalarEvolution>();
DT = &getAnalysis<DominatorTree>();
initialize();
findLoopConditionals();
if (!ExitCondition)
return false;
findSplitCondition();
if (SplitData.empty())
@ -183,24 +196,24 @@ bool LoopIndexSplit::runOnLoop(Loop *IncomingLoop, LPPassManager &LPM) {
/// Return true if V is a induction variable or induction variable's
/// increment for loop L.
bool LoopIndexSplit::SplitInfo::findIndVar(Value *V, Loop *L) {
void LoopIndexSplit::findIndVar(Value *V, Loop *L) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I)
return false;
return;
// Check if I is a phi node from loop header or not.
if (PHINode *PN = dyn_cast<PHINode>(V)) {
if (PN->getParent() == L->getHeader()) {
IndVar = PN;
return true;
IndVar = PN;
return;
}
}
// Check if I is a add instruction whose one operand is
// phi node from loop header and second operand is constant.
if (I->getOpcode() != Instruction::Add)
return false;
return;
Value *Op0 = I->getOperand(0);
Value *Op1 = I->getOperand(1);
@ -210,7 +223,7 @@ bool LoopIndexSplit::SplitInfo::findIndVar(Value *V, Loop *L) {
&& isa<ConstantInt>(Op1)) {
IndVar = PN;
IndVarIncrement = I;
return true;
return;
}
}
@ -219,11 +232,66 @@ bool LoopIndexSplit::SplitInfo::findIndVar(Value *V, Loop *L) {
&& isa<ConstantInt>(Op0)) {
IndVar = PN;
IndVarIncrement = I;
return true;
return;
}
}
return false;
return;
}
// Find loop's exit condition and associated induction variable.
void LoopIndexSplit::findLoopConditionals() {
BasicBlock *ExitBlock = 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)
return;
ExitBlock = BB;
}
if (!ExitBlock)
return;
// If exit block's terminator is conditional branch inst then we have found
// exit condition.
BranchInst *BR = dyn_cast<BranchInst>(ExitBlock->getTerminator());
if (!BR || BR->isUnconditional())
return;
ICmpInst *CI = dyn_cast<ICmpInst>(BR->getCondition());
if (!CI)
return;
ExitCondition = CI;
// Exit condition's one operand is loop invariant exit value and second
// operand is SCEVAddRecExpr based on induction variable.
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)) {
ExitValue = V0;
findIndVar(V1, L);
}
else if (SH1->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH0)) {
ExitValue = V1;
findIndVar(V0, L);
}
if (!ExitValue || !IndVar)
ExitCondition = NULL;
else if (IndVar) {
BasicBlock *Preheader = L->getLoopPreheader();
StartValue = IndVar->getIncomingValueForBlock(Preheader);
}
}
/// Find condition inside a loop that is suitable candidate for index split.
@ -246,7 +314,7 @@ void LoopIndexSplit::findSplitCondition() {
continue;
ICmpInst *CI = dyn_cast<ICmpInst>(BR->getCondition());
if (!CI)
if (!CI || CI == ExitCondition)
return;
// If one operand is loop invariant and second operand is SCEVAddRecExpr
@ -260,14 +328,26 @@ void LoopIndexSplit::findSplitCondition() {
if (SH0->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH1)) {
SD.SplitValue = V0;
SD.SplitCondition = CI;
if (SD.findIndVar(V1, L))
SplitData.push_back(SD);
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);
}
}
else if (SH1->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH0)) {
SD.SplitValue = V1;
SD.SplitCondition = CI;
if (SD.findIndVar(V0, L))
SplitData.push_back(SD);
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);
}
}
}
}
@ -340,7 +420,7 @@ bool LoopIndexSplit::processOneIterationLoop(SplitInfo &SD, LPPassManager &LPM)
BasicBlock *Preheader = L->getLoopPreheader();
Instruction *Terminator = Header->getTerminator();
Value *StartValue = SD.IndVar->getIncomingValueForBlock(Preheader);
StartValue = IndVar->getIncomingValueForBlock(Preheader);
// Replace split condition in header.
// Transform
@ -349,14 +429,14 @@ bool LoopIndexSplit::processOneIterationLoop(SplitInfo &SD, LPPassManager &LPM)
// c1 = icmp uge i32 SplitValue, StartValue
// c2 = icmp ult i32 vSplitValue, ExitValue
// and i32 c1, c2
bool SignedPredicate = SD.ExitCondition->isSignedPredicate();
bool SignedPredicate = ExitCondition->isSignedPredicate();
Instruction *C1 = new ICmpInst(SignedPredicate ?
ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE,
SD.SplitValue, StartValue, "lisplit",
Terminator);
Instruction *C2 = new ICmpInst(SignedPredicate ?
ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
SD.SplitValue, SD.ExitValue, "lisplit",
SD.SplitValue, ExitValue, "lisplit",
Terminator);
Instruction *NSplitCond = BinaryOperator::createAnd(C1, C2, "lisplit",
Terminator);
@ -413,11 +493,11 @@ bool LoopIndexSplit::safeHeader(SplitInfo &SD, BasicBlock *Header) {
continue;
// Induction variable is OK.
if (I == SD.IndVar)
if (I == IndVar)
continue;
// Induction variable increment is OK.
if (I == SD.IndVarIncrement)
if (I == IndVarIncrement)
continue;
// Terminator is also harmless.
@ -444,11 +524,11 @@ bool LoopIndexSplit::safeExitBlock(SplitInfo &SD, BasicBlock *ExitBlock) {
continue;
// Induction variable increment is OK.
if (SD.IndVarIncrement && SD.IndVarIncrement == I)
if (IndVarIncrement && IndVarIncrement == I)
continue;
// Check if I is induction variable increment instruction.
if (!SD.IndVarIncrement && I->getOpcode() == Instruction::Add) {
if (!IndVarIncrement && I->getOpcode() == Instruction::Add) {
Value *Op0 = I->getOperand(0);
Value *Op1 = I->getOperand(1);
@ -457,14 +537,14 @@ bool LoopIndexSplit::safeExitBlock(SplitInfo &SD, BasicBlock *ExitBlock) {
if ((PN = dyn_cast<PHINode>(Op0))) {
if ((CI = dyn_cast<ConstantInt>(Op1)))
SD.IndVarIncrement = I;
IndVarIncrement = I;
} else
if ((PN = dyn_cast<PHINode>(Op1))) {
if ((CI = dyn_cast<ConstantInt>(Op0)))
SD.IndVarIncrement = I;
IndVarIncrement = I;
}
if (SD.IndVarIncrement && PN == SD.IndVar && CI->isOne())
if (IndVarIncrement && PN == IndVar && CI->isOne())
continue;
}
@ -472,38 +552,17 @@ bool LoopIndexSplit::safeExitBlock(SplitInfo &SD, BasicBlock *ExitBlock) {
// Exit condition is OK if it compares loop invariant exit value,
// which is checked below.
else if (ICmpInst *EC = dyn_cast<ICmpInst>(I)) {
++BI;
Instruction *N = BI;
if (N == ExitBlock->getTerminator()) {
SD.ExitCondition = EC;
if (EC == ExitCondition)
continue;
}
}
if (I == ExitBlock->getTerminator())
continue;
// Otherwise we have instruction that may not be safe.
return false;
}
// Check if Exit condition is comparing induction variable against
// loop invariant value. If one operand is induction variable and
// the other operand is loop invaraint then Exit condition is safe.
if (SD.ExitCondition) {
Value *Op0 = SD.ExitCondition->getOperand(0);
Value *Op1 = SD.ExitCondition->getOperand(1);
Instruction *Insn0 = dyn_cast<Instruction>(Op0);
Instruction *Insn1 = dyn_cast<Instruction>(Op1);
if (Insn0 && Insn0 == SD.IndVarIncrement)
SD.ExitValue = Op1;
else if (Insn1 && Insn1 == SD.IndVarIncrement)
SD.ExitValue = Op0;
SCEVHandle ValueSCEV = SE->getSCEV(SD.ExitValue);
if (!ValueSCEV->isLoopInvariant(L))
return false;
}
// We could not find any reason to consider ExitBlock unsafe.
return true;
}
@ -528,6 +587,21 @@ unsigned LoopIndexSplit::findSplitCost(Loop *L, SplitInfo &SD) {
}
bool LoopIndexSplit::splitLoop(SplitInfo &SD) {
// FIXME :)
// True loop is original loop. False loop is cloned loop.
//[*] Calculate True loop's new Exit Value in loop preheader.
// NewExitValue = min(SplitValue, ExitValue)
//[*] Calculate False loop's new Start Value in loop preheader.
// NewStartValue = min(SplitValue, TrueLoop.StartValue)
//[*] Split Exit Edge.
//[*] Clone loop. Avoid true destination of split condition and
// the blocks dominated by true destination.
//[*] True loops exit edge enters False loop.
//[*] Eliminate split condition's false branch from True loop.
// Update true loop dom info.
//[*] Update True loop's exit value using NewExitValue.
//[*] Update False loop's start value using NewStartValue.
//[*] Fix lack of true branch in False loop CFG.
// Update false loop dom info.
//[*] Update dom info in general.
return false;
}