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Revert r230921, "Revert some changes that were made to fix PR20680.", for now.

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It caused a failure on clang/test/Misc/backend-optimization-failure.cpp .

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230929 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
NAKAMURA Takumi
2015-03-02 01:14:03 +00:00
parent 11ec3cfe5d
commit 6cad61163a
4 changed files with 61 additions and 17 deletions
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48
lib/Transforms/Scalar/IndVarSimplify.cpp
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@@ -1705,15 +1705,51 @@ LinearFunctionTestReplace(Loop *L,
// compare against the post-incremented value, otherwise we must compare
// against the preincremented value.
if (L->getExitingBlock() == L->getLoopLatch()) {
// Add one to the "backedge-taken" count to get the trip count.
// 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());
llvm::Value *IncrementedIndvar =
IndVar->getIncomingValueForBlock(L->getExitingBlock());
const auto *IncrementedIndvarSCEV =
cast<SCEVAddRecExpr>(SE->getSCEV(IncrementedIndvar));
// It is unsafe to use the incremented indvar if it has a wrapping flag, we
// don't want to compare against a poison value. Check the SCEV that
// corresponds to the incremented indvar, the SCEVExpander will only insert
// flags in the IR if the SCEV originally had wrapping flags.
// FIXME: In theory, SCEV could drop flags even though they exist in IR.
// A more robust solution would involve getting a new expression for
// CmpIndVar by applying non-NSW/NUW AddExprs.
auto WrappingFlags =
ScalarEvolution::setFlags(SCEV::FlagNUW, SCEV::FlagNSW);
const SCEV *IVInit = IncrementedIndvarSCEV->getStart();
if (SE->getTypeSizeInBits(IVInit->getType()) >
SE->getTypeSizeInBits(IVCount->getType()))
IVInit = SE->getTruncateExpr(IVInit, IVCount->getType());
unsigned BitWidth = SE->getTypeSizeInBits(IVCount->getType());
Type *WideTy = IntegerType::get(SE->getContext(), BitWidth + 1);
// Check if InitIV + BECount+1 requires sign/zero extension.
// If not, clear the corresponding flag from WrappingFlags because it is not
// necessary for those flags in the IncrementedIndvarSCEV expression.
if (SE->getSignExtendExpr(SE->getAddExpr(IVInit, BackedgeTakenCount),
WideTy) ==
SE->getAddExpr(SE->getSignExtendExpr(IVInit, WideTy),
SE->getSignExtendExpr(BackedgeTakenCount, WideTy)))
WrappingFlags = ScalarEvolution::clearFlags(WrappingFlags, SCEV::FlagNSW);
if (SE->getZeroExtendExpr(SE->getAddExpr(IVInit, BackedgeTakenCount),
WideTy) ==
SE->getAddExpr(SE->getZeroExtendExpr(IVInit, WideTy),
SE->getZeroExtendExpr(BackedgeTakenCount, WideTy)))
WrappingFlags = ScalarEvolution::clearFlags(WrappingFlags, SCEV::FlagNUW);
if (!ScalarEvolution::maskFlags(IncrementedIndvarSCEV->getNoWrapFlags(),
WrappingFlags)) {
// Add one to the "backedge-taken" count to get the trip count.
// 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));
CmpIndVar = IncrementedIndvar;
}
}
Value *ExitCnt = genLoopLimit(IndVar, IVCount, L, Rewriter, SE);