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Merging r217115:

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r217115 | majnemer | 2014-09-03 17:23:13 -0700 (Wed, 03 Sep 2014) | 3 lines

IndVarSimplify: Address review comments for r217102

No functional change intended, just some cleanups and comments added.
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_35@223638 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2014-12-08 08:50:39 +00:00
parent 280476e7c6
commit 1c417269c7
1 changed files with 7 additions and 4 deletions
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11
lib/Transforms/Scalar/IndVarSimplify.cpp
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@ -1626,16 +1626,19 @@ LinearFunctionTestReplace(Loop *L,
// 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.
llvm::Value *IncrementedIndvar = 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.
if (ScalarEvolution::maskFlags(IncrementedIndvarSCEV->getNoWrapFlags(),
SCEV::FlagNUW | SCEV::FlagNSW) ==
SCEV::FlagAnyWrap) {
// 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.
if (!ScalarEvolution::maskFlags(IncrementedIndvarSCEV->getNoWrapFlags(),
SCEV::FlagNUW | SCEV::FlagNSW)) {
// 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().