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Handle decrementing loops properly. Fixes PR1533.

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Always pass the constant as the second parameter to HowManyLessThans.

Remove obsolete "isSigned" parameter.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@39893 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky
2007-07-16 02:08:00 +00:00
parent f7b71c64cf
commit eefdebe002
3 changed files with 35 additions and 19 deletions
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lib/Analysis/ScalarEvolution.cpp
+13 -15
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@@ -1671,8 +1671,7 @@ SCEVHandle ScalarEvolutionsImpl::ComputeIterationCount(const Loop *L) {
ConstantRange CompRange(
ICmpInst::makeConstantRange(Cond, CompVal->getValue()));
SCEVHandle Ret = AddRec->getNumIterationsInRange(CompRange,
false /*Always treat as unsigned range*/);
SCEVHandle Ret = AddRec->getNumIterationsInRange(CompRange);
if (!isa<SCEVCouldNotCompute>(Ret)) return Ret;
}
}
@@ -1696,7 +1695,8 @@ SCEVHandle ScalarEvolutionsImpl::ComputeIterationCount(const Loop *L) {
break;
}
case ICmpInst::ICMP_SGT: {
SCEVHandle TC = HowManyLessThans(RHS, LHS, L);
SCEVHandle TC = HowManyLessThans(SCEV::getNegativeSCEV(LHS),
SCEV::getNegativeSCEV(RHS), L);
if (!isa<SCEVCouldNotCompute>(TC)) return TC;
break;
}
@@ -2406,8 +2406,7 @@ HowManyLessThans(SCEV *LHS, SCEV *RHS, const Loop *L) {
/// this is that it returns the first iteration number where the value is not in
/// the condition, thus computing the exit count. If the iteration count can't
/// be computed, an instance of SCEVCouldNotCompute is returned.
SCEVHandle SCEVAddRecExpr::getNumIterationsInRange(ConstantRange Range,
bool isSigned) const {
SCEVHandle SCEVAddRecExpr::getNumIterationsInRange(ConstantRange Range) const {
if (Range.isFullSet()) // Infinite loop.
return new SCEVCouldNotCompute();
@@ -2419,7 +2418,7 @@ SCEVHandle SCEVAddRecExpr::getNumIterationsInRange(ConstantRange Range,
SCEVHandle Shifted = SCEVAddRecExpr::get(Operands, getLoop());
if (SCEVAddRecExpr *ShiftedAddRec = dyn_cast<SCEVAddRecExpr>(Shifted))
return ShiftedAddRec->getNumIterationsInRange(
Range.subtract(SC->getValue()->getValue()),isSigned);
Range.subtract(SC->getValue()->getValue()));
// This is strange and shouldn't happen.
return new SCEVCouldNotCompute();
}
@@ -2443,17 +2442,16 @@ SCEVHandle SCEVAddRecExpr::getNumIterationsInRange(ConstantRange Range,
// If this is an affine expression then we have this situation:
// Solve {0,+,A} in Range === Ax in Range
// Since we know that zero is in the range, we know that the upper value of
// the range must be the first possible exit value. Also note that we
// already checked for a full range.
const APInt &Upper = Range.getUpper();
APInt A = cast<SCEVConstant>(getOperand(1))->getValue()->getValue();
// We know that zero is in the range. If A is positive then we know that
// the upper value of the range must be the first possible exit value.
// If A is negative then the lower of the range is the last possible loop
// value. Also note that we already checked for a full range.
APInt One(getBitWidth(),1);
APInt A = cast<SCEVConstant>(getOperand(1))->getValue()->getValue();
APInt End = A.sge(One) ? (Range.getUpper() - One) : Range.getLower();
// The exit value should be (Upper+A-1)/A.
APInt ExitVal(Upper);
if (A != One)
ExitVal = (Upper + A - One).sdiv(A);
// The exit value should be (End+A)/A.
APInt ExitVal = (End + A).sdiv(A);
ConstantInt *ExitValue = ConstantInt::get(ExitVal);
// Evaluate at the exit value. If we really did fall out of the valid