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It is not safe to execute split condition's true branch first all the time. If split

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condition predicate is GT or GE then execute false branch first.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@41358 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Devang Patel 2007-08-24 06:17:19 +00:00
parent c830aee8e8
commit 4259fe3281
1 changed files with 35 additions and 5 deletions
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40
lib/Transforms/Scalar/LoopIndexSplit.cpp
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@ -57,7 +57,8 @@ namespace {
class SplitInfo {
public:
SplitInfo() : SplitValue(NULL), SplitCondition(NULL) {}
SplitInfo() : SplitValue(NULL), SplitCondition(NULL),
UseTrueBranchFirst(true) {}
// Induction variable's range is split at this value.
Value *SplitValue;
@ -65,10 +66,14 @@ namespace {
// This compare instruction compares IndVar against SplitValue.
ICmpInst *SplitCondition;
// True if after loop index split, first loop will execute split condition's
// true branch.
bool UseTrueBranchFirst;
// Clear split info.
void clear() {
SplitValue = NULL;
SplitCondition = NULL;
UseTrueBranchFirst = true;
}
};
@ -199,6 +204,9 @@ bool LoopIndexSplit::runOnLoop(Loop *IncomingLoop, LPPassManager &LPM_Ref) {
++SI;
}
if (SplitData.empty())
return false;
// Split most profitiable condition.
// FIXME : Implement cost analysis.
unsigned MostProfitableSDIndex = 0;
@ -341,6 +349,14 @@ void LoopIndexSplit::findSplitCondition() {
if (CI->getPredicate() == ICmpInst::ICMP_NE)
return;
// If split condition predicate is GT or GE then first execute
// false branch of split condition.
if (CI->getPredicate() != ICmpInst::ICMP_ULT
&& CI->getPredicate() != ICmpInst::ICMP_SLT
&& CI->getPredicate() != ICmpInst::ICMP_ULE
&& CI->getPredicate() != ICmpInst::ICMP_SLE)
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);
@ -878,16 +894,30 @@ bool LoopIndexSplit::splitLoop(SplitInfo &SD) {
//[*] 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 = A_BR->getSuccessor(1);
BasicBlock *A_ActiveBranch = A_BR->getSuccessor(0);
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_BR->getSuccessor(0));
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 = B_BR->getSuccessor(0);
BasicBlock *B_ActiveBranch = B_BR->getSuccessor(1);
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_BR->getSuccessor(1));
removeBlocks(B_InactiveBranch, BLoop, B_ActiveBranch);