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Cleanup LFTR logic.

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llvm-svn: 186214
This commit is contained in:
Andrew Trick 2013-07-12 22:08:44 +00:00
parent aacd582de2
commit 064fb30cab
1 changed files with 9 additions and 28 deletions
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37
lib/Transforms/Scalar/IndVarSimplify.cpp
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@ -1552,44 +1552,23 @@ LinearFunctionTestReplace(Loop *L,
SCEVExpander &Rewriter) {
assert(canExpandBackedgeTakenCount(L, SE) && "precondition");
// LFTR can ignore IV overflow and truncate to the width of
// BECount. This avoids materializing the add(zext(add)) expression.
Type *CntTy = BackedgeTakenCount->getType();
// Initialize CmpIndVar and IVCount to their preincremented values.
Value *CmpIndVar = IndVar;
const SCEV *IVCount = BackedgeTakenCount;
// If the exiting block is the same as the backedge block, we prefer to
// compare against the post-incremented value, otherwise we must compare
// against the preincremented value.
Value *CmpIndVar;
const SCEV *IVCount;
if (L->getExitingBlock() == L->getLoopLatch()) {
// Add one to the "backedge-taken" count to get the trip count.
// If this addition may overflow, we have to be more pessimistic and
// cast the induction variable before doing the add.
const SCEV *N =
SE->getAddExpr(BackedgeTakenCount,
SE->getConstant(BackedgeTakenCount->getType(), 1));
if (CntTy == BackedgeTakenCount->getType())
IVCount = N;
else {
const SCEV *Zero = SE->getConstant(BackedgeTakenCount->getType(), 0);
if ((isa<SCEVConstant>(N) && !N->isZero()) ||
SE->isLoopEntryGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) {
// No overflow. Cast the sum.
IVCount = SE->getTruncateOrZeroExtend(N, CntTy);
} else {
// Potential overflow. Cast before doing the add.
IVCount = SE->getTruncateOrZeroExtend(BackedgeTakenCount, CntTy);
IVCount = SE->getAddExpr(IVCount, SE->getConstant(CntTy, 1));
}
}
// This addition may overflow, which is valid as long as the comparison is
// truncated to BackedgeTakenCount->getType().
IVCount = SE->getAddExpr(BackedgeTakenCount,
SE->getConstant(BackedgeTakenCount->getType(), 1));
// The BackedgeTaken expression contains the number of times that the
// backedge branches to the loop header. This is one less than the
// number of times the loop executes, so use the incremented indvar.
CmpIndVar = IndVar->getIncomingValueForBlock(L->getExitingBlock());
} else {
// We must use the preincremented value...
IVCount = SE->getTruncateOrZeroExtend(BackedgeTakenCount, CntTy);
CmpIndVar = IndVar;
}
Value *ExitCnt = genLoopLimit(IndVar, IVCount, L, Rewriter, SE);
@ -1611,6 +1590,8 @@ LinearFunctionTestReplace(Loop *L,
<< " RHS:\t" << *ExitCnt << "\n"
<< " IVCount:\t" << *IVCount << "\n");
// LFTR can ignore IV overflow and truncate to the width of
// BECount. This avoids materializing the add(zext(add)) expression.
IRBuilder<> Builder(BI);
if (SE->getTypeSizeInBits(CmpIndVar->getType())
> SE->getTypeSizeInBits(ExitCnt->getType())) {