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Generalize the REM folding code to handle another case Nick Lewycky

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pointed out: realize the AND can provide factors and look through Casts.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26469 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-03-02 06:50:58 +00:00
parent f4eec627d2
commit db3f873bd8
1 changed files with 43 additions and 13 deletions
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56
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -1812,6 +1812,45 @@ Instruction *InstCombiner::visitDiv(BinaryOperator &I) {
}
/// GetFactor - If we can prove that the specified value is at least a multiple
/// of some factor, return that factor.
static Constant *GetFactor(Value *V) {
if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
return CI;
// Unless we can be tricky, we know this is a multiple of 1.
Constant *Result = ConstantInt::get(V->getType(), 1);
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return Result;
if (I->getOpcode() == Instruction::Mul) {
// Handle multiplies by a constant, etc.
return ConstantExpr::getMul(GetFactor(I->getOperand(0)),
GetFactor(I->getOperand(1)));
} else if (I->getOpcode() == Instruction::Shl) {
// (X<<C) -> X * (1 << C)
if (Constant *ShRHS = dyn_cast<Constant>(I->getOperand(1))) {
ShRHS = ConstantExpr::getShl(Result, ShRHS);
return ConstantExpr::getMul(GetFactor(I->getOperand(0)), ShRHS);
}
} else if (I->getOpcode() == Instruction::And) {
if (ConstantInt *RHS = dyn_cast<ConstantInt>(I->getOperand(1))) {
// X & 0xFFF0 is known to be a multiple of 16.
unsigned Zeros = CountTrailingZeros_64(RHS->getZExtValue());
if (Zeros != V->getType()->getPrimitiveSizeInBits())
return ConstantExpr::getShl(Result,
ConstantUInt::get(Type::UByteTy, Zeros));
}
} else if (I->getOpcode() == Instruction::Cast) {
Value *Op = I->getOperand(0);
// Only handle int->int casts.
if (!Op->getType()->isInteger()) return Result;
return ConstantExpr::getCast(GetFactor(Op), V->getType());
}
return Result;
}
Instruction *InstCombiner::visitRem(BinaryOperator &I) {
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
@ -1874,20 +1913,11 @@ Instruction *InstCombiner::visitRem(BinaryOperator &I) {
} else if (isa<PHINode>(Op0I)) {
if (Instruction *NV = FoldOpIntoPhi(I))
return NV;
} else if (Op0I->getOpcode() == Instruction::Mul) {
// X*C1%C2 --> 0 iff C1%C2 == 0
if (ConstantInt *MulRHS = dyn_cast<ConstantInt>(Op0I->getOperand(1))) {
if (ConstantExpr::getRem(MulRHS, RHS)->isNullValue())
return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
}
} else if (Op0I->getOpcode() == Instruction::Shl) {
// (X<<C1)%C2 --> 0 iff (1<<C1)%C2 == 0
if (Constant *ShRHS = dyn_cast<Constant>(Op0I->getOperand(1))) {
ShRHS = ConstantExpr::getShl(ConstantInt::get(I.getType(), 1), ShRHS);
if (ConstantExpr::getRem(ShRHS, RHS)->isNullValue())
return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
}
}
// X*C1%C2 --> 0 iff C1%C2 == 0
if (ConstantExpr::getRem(GetFactor(Op0I), RHS)->isNullValue())
return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
}
}