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Three changes: 

1. Teach GetConstantInType to handle boolean constants.
2. Teach instcombine to fold (compare X, CST) when X has known 0/1 bits.
   Testcase here: set.ll:test22
3. Improve the "(X >> c1) & C2 == 0" folding code to allow a noop cast
   between the shift and and.  More aggressive bitfolding for other reasons
   was turning signed shr's into unsigned shr's, leaving the noop cast in
   the way.

llvm-svn: 26131
This commit is contained in:
Chris Lattner 2006-02-12 02:07:56 +00:00
parent 2234a136b3
commit ee0f280743
1 changed files with 135 additions and 6 deletions
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139
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
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@ -410,9 +410,11 @@ static ConstantInt *SubOne(ConstantInt *C) {
/// GetConstantInType - Return a ConstantInt with the specified type and value.
///
static ConstantInt *GetConstantInType(const Type *Ty, uint64_t Val) {
static ConstantIntegral *GetConstantInType(const Type *Ty, uint64_t Val) {
if (Ty->isUnsigned())
return ConstantUInt::get(Ty, Val);
else if (Ty->getTypeID() == Type::BoolTyID)
return ConstantBool::get(Val);
int64_t SVal = Val;
SVal <<= 64-Ty->getPrimitiveSizeInBits();
SVal >>= 64-Ty->getPrimitiveSizeInBits();
@ -619,6 +621,52 @@ static bool ShrinkDemandedConstant(Instruction *I, unsigned OpNo,
return true;
}
// ComputeSignedMinMaxValuesFromKnownBits - Given a signed integer type and a
// set of known zero and one bits, compute the maximum and minimum values that
// could have the specified known zero and known one bits, returning them in
// min/max.
static void ComputeSignedMinMaxValuesFromKnownBits(const Type *Ty,
uint64_t KnownZero,
uint64_t KnownOne,
int64_t &Min, int64_t &Max) {
uint64_t TypeBits = Ty->getIntegralTypeMask();
uint64_t UnknownBits = ~(KnownZero|KnownOne) & TypeBits;
uint64_t SignBit = 1ULL << (Ty->getPrimitiveSizeInBits()-1);
// The minimum value is when all unknown bits are zeros, EXCEPT for the sign
// bit if it is unknown.
Min = KnownOne;
Max = KnownOne|UnknownBits;
if (SignBit & UnknownBits) { // Sign bit is unknown
Min |= SignBit;
Max &= ~SignBit;
}
// Sign extend the min/max values.
int ShAmt = 64-Ty->getPrimitiveSizeInBits();
Min = (Min << ShAmt) >> ShAmt;
Max = (Max << ShAmt) >> ShAmt;
}
// ComputeUnsignedMinMaxValuesFromKnownBits - Given an unsigned integer type and
// a set of known zero and one bits, compute the maximum and minimum values that
// could have the specified known zero and known one bits, returning them in
// min/max.
static void ComputeUnsignedMinMaxValuesFromKnownBits(const Type *Ty,
uint64_t KnownZero,
uint64_t KnownOne,
uint64_t &Min,
uint64_t &Max) {
uint64_t TypeBits = Ty->getIntegralTypeMask();
uint64_t UnknownBits = ~(KnownZero|KnownOne) & TypeBits;
// The minimum value is when the unknown bits are all zeros.
Min = KnownOne;
// The maximum value is when the unknown bits are all ones.
Max = KnownOne|UnknownBits;
}
/// SimplifyDemandedBits - Look at V. At this point, we know that only the
@ -3264,6 +3312,69 @@ Instruction *InstCombiner::visitSetCondInst(SetCondInst &I) {
if (I.getOpcode() == Instruction::SetGE)
return BinaryOperator::createSetGT(Op0, SubOne(CI));
// See if we can fold the comparison based on bits known to be zero or one
// in the input.
uint64_t KnownZero, KnownOne;
if (SimplifyDemandedBits(Op0, Ty->getIntegralTypeMask(),
KnownZero, KnownOne, 0))
return &I;
// Given the known and unknown bits, compute a range that the LHS could be
// in.
if (KnownOne | KnownZero) {
if (Ty->isUnsigned()) { // Unsigned comparison.
uint64_t Min, Max;
uint64_t RHSVal = CI->getZExtValue();
ComputeUnsignedMinMaxValuesFromKnownBits(Ty, KnownZero, KnownOne,
Min, Max);
switch (I.getOpcode()) { // LE/GE have been folded already.
default: assert(0 && "Unknown setcc opcode!");
case Instruction::SetEQ:
if (Max < RHSVal || Min > RHSVal)
return ReplaceInstUsesWith(I, ConstantBool::False);
break;
case Instruction::SetNE:
if (Max < RHSVal || Min > RHSVal)
return ReplaceInstUsesWith(I, ConstantBool::True);
break;
case Instruction::SetLT:
if (Max < RHSVal) return ReplaceInstUsesWith(I, ConstantBool::True);
if (Min > RHSVal) return ReplaceInstUsesWith(I, ConstantBool::False);
break;
case Instruction::SetGT:
if (Min > RHSVal) return ReplaceInstUsesWith(I, ConstantBool::True);
if (Max < RHSVal) return ReplaceInstUsesWith(I, ConstantBool::False);
break;
}
} else { // Signed comparison.
int64_t Min, Max;
int64_t RHSVal = CI->getSExtValue();
ComputeSignedMinMaxValuesFromKnownBits(Ty, KnownZero, KnownOne,
Min, Max);
switch (I.getOpcode()) { // LE/GE have been folded already.
default: assert(0 && "Unknown setcc opcode!");
case Instruction::SetEQ:
if (Max < RHSVal || Min > RHSVal)
return ReplaceInstUsesWith(I, ConstantBool::False);
break;
case Instruction::SetNE:
if (Max < RHSVal || Min > RHSVal)
return ReplaceInstUsesWith(I, ConstantBool::True);
break;
case Instruction::SetLT:
if (Max < RHSVal) return ReplaceInstUsesWith(I, ConstantBool::True);
if (Min > RHSVal) return ReplaceInstUsesWith(I, ConstantBool::False);
break;
case Instruction::SetGT:
if (Min > RHSVal) return ReplaceInstUsesWith(I, ConstantBool::True);
if (Max < RHSVal) return ReplaceInstUsesWith(I, ConstantBool::False);
break;
}
}
}
if (Instruction *LHSI = dyn_cast<Instruction>(Op0))
switch (LHSI->getOpcode()) {
case Instruction::And:
@ -3274,17 +3385,28 @@ Instruction *InstCombiner::visitSetCondInst(SetCondInst &I) {
// happens a LOT in code produced by the C front-end, for bitfield
// access.
ShiftInst *Shift = dyn_cast<ShiftInst>(LHSI->getOperand(0));
ConstantInt *AndCST = cast<ConstantInt>(LHSI->getOperand(1));
// Check to see if there is a noop-cast between the shift and the and.
if (!Shift) {
if (CastInst *CI = dyn_cast<CastInst>(LHSI->getOperand(0)))
if (CI->getOperand(0)->getType()->isIntegral() &&
CI->getOperand(0)->getType()->getPrimitiveSizeInBits() ==
CI->getType()->getPrimitiveSizeInBits())
Shift = dyn_cast<ShiftInst>(CI->getOperand(0));
}
ConstantUInt *ShAmt;
ShAmt = Shift ? dyn_cast<ConstantUInt>(Shift->getOperand(1)) : 0;
ConstantInt *AndCST = cast<ConstantInt>(LHSI->getOperand(1));
const Type *Ty = LHSI->getType();
const Type *Ty = Shift ? Shift->getType() : 0; // Type of the shift.
const Type *AndTy = AndCST->getType(); // Type of the and.
// We can fold this as long as we can't shift unknown bits
// into the mask. This can only happen with signed shift
// rights, as they sign-extend.
if (ShAmt) {
bool CanFold = Shift->getOpcode() != Instruction::Shr ||
Shift->getType()->isUnsigned();
Ty->isUnsigned();
if (!CanFold) {
// To test for the bad case of the signed shr, see if any
// of the bits shifted in could be tested after the mask.
@ -3293,7 +3415,8 @@ Instruction *InstCombiner::visitSetCondInst(SetCondInst &I) {
Constant *OShAmt = ConstantUInt::get(Type::UByteTy, ShAmtVal);
Constant *ShVal =
ConstantExpr::getShl(ConstantInt::getAllOnesValue(Ty), OShAmt);
ConstantExpr::getShl(ConstantInt::getAllOnesValue(AndTy),
OShAmt);
if (ConstantExpr::getAnd(ShVal, AndCST)->isNullValue())
CanFold = true;
}
@ -3323,7 +3446,13 @@ Instruction *InstCombiner::visitSetCondInst(SetCondInst &I) {
else
NewAndCST = ConstantExpr::getShl(AndCST, ShAmt);
LHSI->setOperand(1, NewAndCST);
if (AndTy == Ty)
LHSI->setOperand(0, Shift->getOperand(0));
else {
Value *NewCast = InsertCastBefore(Shift->getOperand(0), AndTy,
*Shift);
LHSI->setOperand(0, NewCast);
}
WorkList.push_back(Shift); // Shift is dead.
AddUsesToWorkList(I);
return &I;