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IndVarSimplify: Address review comments for r217102

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No functional change intended, just some cleanups and comments added.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217115 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2014-09-04 00:23:13 +00:00
parent b79ed97962
commit e35ac41a3a
1 changed files with 7 additions and 4 deletions
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11
lib/Transforms/Scalar/IndVarSimplify.cpp
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@ -1644,16 +1644,19 @@ LinearFunctionTestReplace(Loop *L,
// The BackedgeTaken expression contains the number of times that the // The BackedgeTaken expression contains the number of times that the
// backedge branches to the loop header. This is one less than the // backedge branches to the loop header. This is one less than the
// number of times the loop executes, so use the incremented indvar. // number of times the loop executes, so use the incremented indvar.
llvm::Value *IncrementedIndvar = IndVar->getIncomingValueForBlock(L->getExitingBlock()); llvm::Value *IncrementedIndvar =
IndVar->getIncomingValueForBlock(L->getExitingBlock());
const auto *IncrementedIndvarSCEV = const auto *IncrementedIndvarSCEV =
cast<SCEVAddRecExpr>(SE->getSCEV(IncrementedIndvar)); cast<SCEVAddRecExpr>(SE->getSCEV(IncrementedIndvar));
// It is unsafe to use the incremented indvar if it has a wrapping flag, we // 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 // don't want to compare against a poison value. Check the SCEV that
// corresponds to the incremented indvar, the SCEVExpander will only insert // corresponds to the incremented indvar, the SCEVExpander will only insert
// flags in the IR if the SCEV originally had wrapping flags. // flags in the IR if the SCEV originally had wrapping flags.
if (ScalarEvolution::maskFlags(IncrementedIndvarSCEV->getNoWrapFlags(), // FIXME: In theory, SCEV could drop flags even though they exist in IR.
SCEV::FlagNUW | SCEV::FlagNSW) == // A more robust solution would involve getting a new expression for
SCEV::FlagAnyWrap) { // CmpIndVar by applying non-NSW/NUW AddExprs.
if (!ScalarEvolution::maskFlags(IncrementedIndvarSCEV->getNoWrapFlags(),
SCEV::FlagNUW | SCEV::FlagNSW)) {
// Add one to the "backedge-taken" count to get the trip count. // 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 // This addition may overflow, which is valid as long as the comparison is
// truncated to BackedgeTakenCount->getType(). // truncated to BackedgeTakenCount->getType().