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Implement shift-simplify.ll:test3, turning:

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(X << 31) <s 0  --> (X&1) != 0

This happens dozens of times in the CFE.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@39879 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2007-07-15 20:42:37 +00:00
parent 28753f8df2
commit a0141b90a3
2 changed files with 123 additions and 103 deletions
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219
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -2271,26 +2271,21 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
return 0;
}
/// isSignBitCheck - Given an exploded icmp instruction, return true if it
/// really just returns true if the most significant (sign) bit is set.
static bool isSignBitCheck(ICmpInst::Predicate pred, ConstantInt *RHS) {
/// isSignBitCheck - Given an exploded icmp instruction, return true if the
/// comparison only checks the sign bit. If it only checks the sign bit, set
/// TrueIfSigned if the result of the comparison is true when the input value is
/// signed.
static bool isSignBitCheck(ICmpInst::Predicate pred, ConstantInt *RHS,
bool &TrueIfSigned) {
switch (pred) {
case ICmpInst::ICMP_SLT:
// True if LHS s< RHS and RHS == 0
return RHS->isZero();
case ICmpInst::ICMP_SLE:
// True if LHS s<= RHS and RHS == -1
return RHS->isAllOnesValue();
case ICmpInst::ICMP_UGE:
// True if LHS u>= RHS and RHS == high-bit-mask (2^7, 2^15, 2^31, etc)
return RHS->getValue() ==
APInt::getSignBit(RHS->getType()->getPrimitiveSizeInBits());
case ICmpInst::ICMP_UGT:
// True if LHS u> RHS and RHS == high-bit-mask - 1
return RHS->getValue() ==
APInt::getSignedMaxValue(RHS->getType()->getPrimitiveSizeInBits());
default:
return false;
case ICmpInst::ICMP_SLT: // True if LHS s< 0
TrueIfSigned = true;
return RHS->isZero();
case ICmpInst::ICMP_SGT: // True if LHS s> -1
TrueIfSigned = false;
return RHS->isAllOnesValue();
default:
return false;
}
}
@ -2377,11 +2372,13 @@ Instruction *InstCombiner::visitMul(BinaryOperator &I) {
if (ICmpInst *SCI = dyn_cast<ICmpInst>(BoolCast->getOperand(0))) {
Value *SCIOp0 = SCI->getOperand(0), *SCIOp1 = SCI->getOperand(1);
const Type *SCOpTy = SCIOp0->getType();
bool TIS = false;
// If the icmp is true iff the sign bit of X is set, then convert this
// multiply into a shift/and combination.
if (isa<ConstantInt>(SCIOp1) &&
isSignBitCheck(SCI->getPredicate(), cast<ConstantInt>(SCIOp1))) {
isSignBitCheck(SCI->getPredicate(), cast<ConstantInt>(SCIOp1), TIS) &&
TIS) {
// Shift the X value right to turn it into "all signbits".
Constant *Amt = ConstantInt::get(SCIOp0->getType(),
SCOpTy->getPrimitiveSizeInBits()-1);
@ -2805,23 +2802,19 @@ Instruction *InstCombiner::visitFRem(BinaryOperator &I) {
// isMaxValueMinusOne - return true if this is Max-1
static bool isMaxValueMinusOne(const ConstantInt *C, bool isSigned) {
uint32_t TypeBits = C->getType()->getPrimitiveSizeInBits();
if (isSigned) {
// Calculate 0111111111..11111
APInt Val(APInt::getSignedMaxValue(TypeBits));
return C->getValue() == Val-1;
}
return C->getValue() == APInt::getAllOnesValue(TypeBits) - 1;
if (!isSigned)
return C->getValue() == APInt::getAllOnesValue(TypeBits) - 1;
return C->getValue() == APInt::getSignedMaxValue(TypeBits)-1;
}
// isMinValuePlusOne - return true if this is Min+1
static bool isMinValuePlusOne(const ConstantInt *C, bool isSigned) {
if (isSigned) {
// Calculate 1111111111000000000000
uint32_t TypeBits = C->getType()->getPrimitiveSizeInBits();
APInt Val(APInt::getSignedMinValue(TypeBits));
return C->getValue() == Val+1;
}
return C->getValue() == 1; // unsigned
if (!isSigned)
return C->getValue() == 1; // unsigned
// Calculate 1111111111000000000000
uint32_t TypeBits = C->getType()->getPrimitiveSizeInBits();
return C->getValue() == APInt::getSignedMinValue(TypeBits)+1;
}
// isOneBitSet - Return true if there is exactly one bit set in the specified
@ -5415,85 +5408,105 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
}
break;
case Instruction::Shl: // (icmp pred (shl X, ShAmt), CI)
if (ConstantInt *ShAmt = dyn_cast<ConstantInt>(LHSI->getOperand(1))) {
if (ICI.isEquality()) {
uint32_t TypeBits = RHSV.getBitWidth();
case Instruction::Shl: { // (icmp pred (shl X, ShAmt), CI)
ConstantInt *ShAmt = dyn_cast<ConstantInt>(LHSI->getOperand(1));
if (!ShAmt) break;
uint32_t TypeBits = RHSV.getBitWidth();
// Check that the shift amount is in range. If not, don't perform
// undefined shifts. When the shift is visited it will be
// simplified.
if (ShAmt->uge(TypeBits))
break;
if (ICI.isEquality()) {
// If we are comparing against bits always shifted out, the
// comparison cannot succeed.
Constant *Comp =
ConstantExpr::getShl(ConstantExpr::getLShr(RHS, ShAmt), ShAmt);
if (Comp != RHS) {// Comparing against a bit that we know is zero.
bool IsICMP_NE = ICI.getPredicate() == ICmpInst::ICMP_NE;
Constant *Cst = ConstantInt::get(Type::Int1Ty, IsICMP_NE);
return ReplaceInstUsesWith(ICI, Cst);
}
if (LHSI->hasOneUse()) {
// Otherwise strength reduce the shift into an and.
uint32_t ShAmtVal = (uint32_t)ShAmt->getLimitedValue(TypeBits);
Constant *Mask =
ConstantInt::get(APInt::getLowBitsSet(TypeBits, TypeBits-ShAmtVal));
// Check that the shift amount is in range. If not, don't perform
// undefined shifts. When the shift is visited it will be
// simplified.
if (ShAmt->uge(TypeBits))
break;
// If we are comparing against bits always shifted out, the
// comparison cannot succeed.
Constant *Comp =
ConstantExpr::getShl(ConstantExpr::getLShr(RHS, ShAmt), ShAmt);
if (Comp != RHS) {// Comparing against a bit that we know is zero.
bool IsICMP_NE = ICI.getPredicate() == ICmpInst::ICMP_NE;
Constant *Cst = ConstantInt::get(Type::Int1Ty, IsICMP_NE);
return ReplaceInstUsesWith(ICI, Cst);
}
if (LHSI->hasOneUse()) {
// Otherwise strength reduce the shift into an and.
uint32_t ShAmtVal = (uint32_t)ShAmt->getLimitedValue(TypeBits);
Constant *Mask =
ConstantInt::get(APInt::getLowBitsSet(TypeBits, TypeBits-ShAmtVal));
Instruction *AndI =
BinaryOperator::createAnd(LHSI->getOperand(0),
Mask, LHSI->getName()+".mask");
Value *And = InsertNewInstBefore(AndI, ICI);
return new ICmpInst(ICI.getPredicate(), And,
ConstantInt::get(RHSV.lshr(ShAmtVal)));
}
Instruction *AndI =
BinaryOperator::createAnd(LHSI->getOperand(0),
Mask, LHSI->getName()+".mask");
Value *And = InsertNewInstBefore(AndI, ICI);
return new ICmpInst(ICI.getPredicate(), And,
ConstantInt::get(RHSV.lshr(ShAmtVal)));
}
}
// Otherwise, if this is a comparison of the sign bit, simplify to and/test.
bool TrueIfSigned = false;
if (LHSI->hasOneUse() &&
isSignBitCheck(ICI.getPredicate(), RHS, TrueIfSigned)) {
// (X << 31) <s 0 --> (X&1) != 0
Constant *Mask = ConstantInt::get(APInt(TypeBits, 1) <<
(TypeBits-ShAmt->getZExtValue()-1));
Instruction *AndI =
BinaryOperator::createAnd(LHSI->getOperand(0),
Mask, LHSI->getName()+".mask");
Value *And = InsertNewInstBefore(AndI, ICI);
return new ICmpInst(TrueIfSigned ? ICmpInst::ICMP_NE : ICmpInst::ICMP_EQ,
And, Constant::getNullValue(And->getType()));
}
break;
}
case Instruction::LShr: // (icmp pred (shr X, ShAmt), CI)
case Instruction::AShr:
if (ConstantInt *ShAmt = dyn_cast<ConstantInt>(LHSI->getOperand(1))) {
if (ICI.isEquality()) {
// Check that the shift amount is in range. If not, don't perform
// undefined shifts. When the shift is visited it will be
// simplified.
uint32_t TypeBits = RHSV.getBitWidth();
if (ShAmt->uge(TypeBits))
break;
uint32_t ShAmtVal = (uint32_t)ShAmt->getLimitedValue(TypeBits);
case Instruction::AShr: {
ConstantInt *ShAmt = dyn_cast<ConstantInt>(LHSI->getOperand(1));
if (!ShAmt) break;
if (ICI.isEquality()) {
// Check that the shift amount is in range. If not, don't perform
// undefined shifts. When the shift is visited it will be
// simplified.
uint32_t TypeBits = RHSV.getBitWidth();
if (ShAmt->uge(TypeBits))
break;
uint32_t ShAmtVal = (uint32_t)ShAmt->getLimitedValue(TypeBits);
// If we are comparing against bits always shifted out, the
// comparison cannot succeed.
APInt Comp = RHSV << ShAmtVal;
if (LHSI->getOpcode() == Instruction::LShr)
Comp = Comp.lshr(ShAmtVal);
else
Comp = Comp.ashr(ShAmtVal);
if (Comp != RHSV) { // Comparing against a bit that we know is zero.
bool IsICMP_NE = ICI.getPredicate() == ICmpInst::ICMP_NE;
Constant *Cst = ConstantInt::get(Type::Int1Ty, IsICMP_NE);
return ReplaceInstUsesWith(ICI, Cst);
}
if (LHSI->hasOneUse() || RHSV == 0) {
// Otherwise strength reduce the shift into an and.
APInt Val(APInt::getHighBitsSet(TypeBits, TypeBits - ShAmtVal));
Constant *Mask = ConstantInt::get(Val);
// If we are comparing against bits always shifted out, the
// comparison cannot succeed.
APInt Comp = RHSV << ShAmtVal;
if (LHSI->getOpcode() == Instruction::LShr)
Comp = Comp.lshr(ShAmtVal);
else
Comp = Comp.ashr(ShAmtVal);
if (Comp != RHSV) { // Comparing against a bit that we know is zero.
bool IsICMP_NE = ICI.getPredicate() == ICmpInst::ICMP_NE;
Constant *Cst = ConstantInt::get(Type::Int1Ty, IsICMP_NE);
return ReplaceInstUsesWith(ICI, Cst);
}
if (LHSI->hasOneUse() || RHSV == 0) {
// Otherwise strength reduce the shift into an and.
APInt Val(APInt::getHighBitsSet(TypeBits, TypeBits - ShAmtVal));
Constant *Mask = ConstantInt::get(Val);
Instruction *AndI =
BinaryOperator::createAnd(LHSI->getOperand(0),
Mask, LHSI->getName()+".mask");
Value *And = InsertNewInstBefore(AndI, ICI);
return new ICmpInst(ICI.getPredicate(), And,
ConstantExpr::getShl(RHS, ShAmt));
}
Instruction *AndI =
BinaryOperator::createAnd(LHSI->getOperand(0),
Mask, LHSI->getName()+".mask");
Value *And = InsertNewInstBefore(AndI, ICI);
return new ICmpInst(ICI.getPredicate(), And,
ConstantExpr::getShl(RHS, ShAmt));
}
}
break;
}
case Instruction::SDiv:
case Instruction::UDiv:

7
test/Transforms/InstCombine/shift-simplify.ll
View File

@ -21,3 +21,10 @@ define i32 @test2(i32 %A, i32 %B, i32 %C) {
%Z = xor i32 %X, %Y
ret i32 %Z
}
define i1 @test3(i32 %X) {
%tmp1 = shl i32 %X, 7
%tmp2 = icmp slt i32 %tmp1, 0
ret i1 %tmp2
}