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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.

llvm-svn: 39893
This commit is contained in:
Nick Lewycky 2007-07-16 02:08:00 +00:00
parent 03bc1d9018
commit 43e5fd5be7
3 changed files with 35 additions and 19 deletions
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6
include/llvm/Analysis/ScalarEvolutionExpressions.h
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@ -475,10 +475,8 @@ namespace llvm {
/// looking at 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. The isSigned parameter indicates whether the ConstantRange
/// should be treated as signed or unsigned.
SCEVHandle getNumIterationsInRange(ConstantRange Range,
bool isSigned) const;
/// returned.
SCEVHandle getNumIterationsInRange(ConstantRange Range) const;
SCEVHandle replaceSymbolicValuesWithConcrete(const SCEVHandle &Sym,
const SCEVHandle &Conc) const;

28
lib/Analysis/ScalarEvolution.cpp
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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

20
test/Analysis/ScalarEvolution/2007-07-15-NegativeStride.ll Normal file
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@ -0,0 +1,20 @@
; RUN: llvm-as < %s | opt -analyze -scalar-evolution 2>&1 | grep "Loop bb: 100 iterations"
; PR1533
@array = weak global [101 x i32] zeroinitializer, align 32 ; <[100 x i32]*> [#uses=1]
define void @loop(i32 %x) {
entry:
br label %bb
bb: ; preds = %bb, %entry
%i.01.0 = phi i32 [ 100, %entry ], [ %tmp4, %bb ] ; <i32> [#uses=2]
%tmp1 = getelementptr [101 x i32]* @array, i32 0, i32 %i.01.0 ; <i32*> [#uses=1]
store i32 %x, i32* %tmp1
%tmp4 = add i32 %i.01.0, -1 ; <i32> [#uses=2]
%tmp7 = icmp sgt i32 %tmp4, -1 ; <i1> [#uses=1]
br i1 %tmp7, label %bb, label %return
return: ; preds = %bb
ret void
}