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[LFTR] Rename variable to minimize confusion [NFC] 

As pointed out by Nikita in D62625, BackedgeTakenCount is generally used to refer to the backedge taken count of the loop.  A conditional backedge taken count - one which only applies if a particular exit is taken - is called a ExitCount in SCEV code, so be consistent here.

llvm-svn: 363293
This commit is contained in:
Philip Reames 2019-06-13 18:40:15 +00:00
parent 42a3fc133d
commit c37be29634
1 changed files with 15 additions and 18 deletions
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33
llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
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@ -151,7 +151,7 @@ class IndVarSimplify {
bool hasHardUserWithinLoop(const Loop *L, const Instruction *I) const;
bool linearFunctionTestReplace(Loop *L, BasicBlock *ExitingBB,
const SCEV *BackedgeTakenCount,
const SCEV *ExitCount,
PHINode *IndVar, SCEVExpander &Rewriter);
bool sinkUnusedInvariants(Loop *L);
@ -2382,8 +2382,7 @@ static Value *genLoopLimit(PHINode *IndVar, BasicBlock *ExitingBB,
/// determine a loop-invariant trip count of the loop, which is actually a much
/// broader range than just linear tests.
bool IndVarSimplify::
linearFunctionTestReplace(Loop *L, BasicBlock *ExitingBB,
const SCEV *BackedgeTakenCount,
linearFunctionTestReplace(Loop *L, BasicBlock *ExitingBB, const SCEV *ExitCount,
PHINode *IndVar, SCEVExpander &Rewriter) {
assert(isLoopCounter(IndVar, L, SE));
assert(L->getLoopLatch() && "Loop no longer in simplified form?");
@ -2392,7 +2391,7 @@ linearFunctionTestReplace(Loop *L, BasicBlock *ExitingBB,
// Initialize CmpIndVar and IVCount to their preincremented values.
Value *CmpIndVar = IndVar;
const SCEV *IVCount = BackedgeTakenCount;
const SCEV *IVCount = ExitCount;
// If the exiting block is the same as the backedge block, we prefer to
// compare against the post-incremented value, otherwise we must compare
@ -2412,10 +2411,9 @@ linearFunctionTestReplace(Loop *L, BasicBlock *ExitingBB,
if (SafeToPostInc) {
// 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->getOne(BackedgeTakenCount->getType()));
// The BackedgeTaken expression contains the number of times that the
// is truncated to ExitCount->getType().
IVCount = SE->getAddExpr(ExitCount, SE->getOne(ExitCount->getType()));
// The ExitCount 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 = IncVar;
@ -2481,9 +2479,9 @@ linearFunctionTestReplace(Loop *L, BasicBlock *ExitingBB,
if (isa<SCEVConstant>(ARStart) && isa<SCEVConstant>(IVCount)) {
const APInt &Start = cast<SCEVConstant>(ARStart)->getAPInt();
APInt Count = cast<SCEVConstant>(IVCount)->getAPInt();
// Note that the post-inc value of BackedgeTakenCount may have overflowed
// Note that the post-inc value of ExitCount may have overflowed
// above such that IVCount is now zero.
if (IVCount != BackedgeTakenCount && Count == 0) {
if (IVCount != ExitCount && Count == 0) {
Count = APInt::getMaxValue(Count.getBitWidth()).zext(CmpIndVarSize);
++Count;
}
@ -2710,21 +2708,21 @@ bool IndVarSimplify::run(Loop *L) {
if (!needsLFTR(L, ExitingBB))
continue;
const SCEV *BETakenCount = SE->getExitCount(L, ExitingBB);
if (isa<SCEVCouldNotCompute>(BETakenCount))
const SCEV *ExitCount = SE->getExitCount(L, ExitingBB);
if (isa<SCEVCouldNotCompute>(ExitCount))
continue;
// Better to fold to true (TODO: do so!)
if (BETakenCount->isZero())
if (ExitCount->isZero())
continue;
PHINode *IndVar = FindLoopCounter(L, ExitingBB, BETakenCount, SE, DT);
PHINode *IndVar = FindLoopCounter(L, ExitingBB, ExitCount, SE, DT);
if (!IndVar)
continue;
// Avoid high cost expansions. Note: This heuristic is questionable in
// that our definition of "high cost" is not exactly principled.
if (Rewriter.isHighCostExpansion(BETakenCount, L))
if (Rewriter.isHighCostExpansion(ExitCount, L))
continue;
// Check preconditions for proper SCEVExpander operation. SCEV does not
@ -2736,10 +2734,9 @@ bool IndVarSimplify::run(Loop *L) {
//
// FIXME: SCEV expansion has no way to bail out, so the caller must
// explicitly check any assumptions made by SCEV. Brittle.
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(BETakenCount);
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(ExitCount);
if (!AR || AR->getLoop()->getLoopPreheader())
Changed |= linearFunctionTestReplace(L, ExitingBB,
BETakenCount, IndVar,
Changed |= linearFunctionTestReplace(L, ExitingBB, ExitCount, IndVar,
Rewriter);
}
}