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For PR1248: 

* Fix some indentation and comments in InsertRangeTest
* Add an "IsSigned" parameter to AddWithOverflow and make it handle signed
  additions. Also, APIntify this function so it works with any bitwidth.
* For the icmp pred ([us]div %X, C1), C2 transforms, exit early if the
  div instruction's RHS is zero.
* Finally, for icmp pred (sdiv %X, C1), -C2, fix an off-by-one error. The
  HiBound needs to be incremented in order to get the range test correct.

llvm-svn: 35247
This commit is contained in:
Reid Spencer 2007-03-21 23:19:50 +00:00
parent 925e8aa370
commit f40711637f
1 changed files with 26 additions and 18 deletions
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44
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -3773,7 +3773,7 @@ Instruction *InstCombiner::InsertRangeTest(Value *V, Constant *Lo, Constant *Hi,
// V >= Min && V < Hi --> V < Hi
if (cast<ConstantInt>(Lo)->isMinValue(isSigned)) {
ICmpInst::Predicate pred = (isSigned ?
ICmpInst::Predicate pred = (isSigned ?
ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT);
return new ICmpInst(pred, V, Hi);
}
@ -3789,7 +3789,7 @@ Instruction *InstCombiner::InsertRangeTest(Value *V, Constant *Lo, Constant *Hi,
if (Lo == Hi) // Trivially true.
return new ICmpInst(ICmpInst::ICMP_EQ, V, V);
// V < Min || V >= Hi ->'V > Hi-1'
// V < Min || V >= Hi -> V > Hi-1
Hi = SubOne(cast<ConstantInt>(Hi));
if (cast<ConstantInt>(Lo)->isMinValue(isSigned)) {
ICmpInst::Predicate pred = (isSigned ?
@ -3797,8 +3797,9 @@ Instruction *InstCombiner::InsertRangeTest(Value *V, Constant *Lo, Constant *Hi,
return new ICmpInst(pred, V, Hi);
}
// Emit V-Lo > Hi-1-Lo
Constant *NegLo = ConstantExpr::getNeg(Lo);
// Emit V-Lo >u Hi-1-Lo
// Note that Hi has already had one subtracted from it, above.
ConstantInt *NegLo = cast<ConstantInt>(ConstantExpr::getNeg(Lo));
Instruction *Add = BinaryOperator::createAdd(V, NegLo, V->getName()+".off");
InsertNewInstBefore(Add, IB);
Constant *LowerBound = ConstantExpr::getAdd(NegLo, Hi);
@ -4918,11 +4919,16 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
/// AddWithOverflow - Compute Result = In1+In2, returning true if the result
/// overflowed for this type.
static bool AddWithOverflow(ConstantInt *&Result, ConstantInt *In1,
ConstantInt *In2) {
ConstantInt *In2, bool IsSigned = false) {
Result = cast<ConstantInt>(ConstantExpr::getAdd(In1, In2));
return cast<ConstantInt>(Result)->getZExtValue() <
cast<ConstantInt>(In1)->getZExtValue();
if (IsSigned)
if (In2->getValue().isNegative())
return Result->getValue().sgt(In1->getValue());
else
return Result->getValue().slt(In1->getValue());
else
return Result->getValue().ult(In1->getValue());
}
/// EmitGEPOffset - Given a getelementptr instruction/constantexpr, emit the
@ -5664,6 +5670,8 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
bool DivIsSigned = LHSI->getOpcode() == Instruction::SDiv;
if (!I.isEquality() && DivIsSigned != I.isSignedPredicate())
break;
if (DivRHS->isZero())
break; // Don't hack on div by zero
// Initialize the variables that will indicate the nature of the
// range check.
@ -5680,19 +5688,17 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
// Determine if the product overflows by seeing if the product is
// not equal to the divide. Make sure we do the same kind of divide
// as in the LHS instruction that we're folding.
bool ProdOV = !DivRHS->isNullValue() &&
(DivIsSigned ? ConstantExpr::getSDiv(Prod, DivRHS) :
ConstantExpr::getUDiv(Prod, DivRHS)) != CI;
bool ProdOV = (DivIsSigned ? ConstantExpr::getSDiv(Prod, DivRHS) :
ConstantExpr::getUDiv(Prod, DivRHS)) != CI;
// Get the ICmp opcode
ICmpInst::Predicate predicate = I.getPredicate();
if (DivRHS->isNullValue()) {
// Don't hack on divide by zeros!
} else if (!DivIsSigned) { // udiv
if (!DivIsSigned) { // udiv
LoBound = Prod;
LoOverflow = ProdOV;
HiOverflow = ProdOV || AddWithOverflow(HiBound, LoBound, DivRHS);
HiOverflow = ProdOV ||
AddWithOverflow(HiBound, LoBound, DivRHS, false);
} else if (DivRHS->getValue().isPositive()) { // Divisor is > 0.
if (CI->isNullValue()) { // (X / pos) op 0
// Can't overflow.
@ -5701,12 +5707,13 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
} else if (CI->getValue().isPositive()) { // (X / pos) op pos
LoBound = Prod;
LoOverflow = ProdOV;
HiOverflow = ProdOV || AddWithOverflow(HiBound, Prod, DivRHS);
HiOverflow = ProdOV ||
AddWithOverflow(HiBound, Prod, DivRHS, true);
} else { // (X / pos) op neg
Constant *DivRHSH = ConstantExpr::getNeg(SubOne(DivRHS));
LoOverflow = AddWithOverflow(LoBound, Prod,
cast<ConstantInt>(DivRHSH));
HiBound = Prod;
cast<ConstantInt>(DivRHSH), true);
HiBound = AddOne(Prod);
HiOverflow = ProdOV;
}
} else { // Divisor is < 0.
@ -5718,7 +5725,8 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
} else if (CI->getValue().isPositive()) { // (X / neg) op pos
HiOverflow = LoOverflow = ProdOV;
if (!LoOverflow)
LoOverflow = AddWithOverflow(LoBound, Prod, AddOne(DivRHS));
LoOverflow = AddWithOverflow(LoBound, Prod, AddOne(DivRHS),
true);
HiBound = AddOne(Prod);
} else { // (X / neg) op neg
LoBound = Prod;