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Change cannonicalization rules: add X,X is represented as multiplies, multiplies

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of a power of two are represented as a shift.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@7803 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2003-08-13 04:18:28 +00:00
parent 48e6079478
commit e92d2f450a
1 changed files with 24 additions and 8 deletions
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32
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -19,6 +19,9 @@
// shifts are performed first, then or's, then and's, then xor's.
// 3. SetCC instructions are converted from <,>,<=,>= to ==,!= if possible
// 4. All SetCC instructions on boolean values are replaced with logical ops
// 5. add X, X is represented as (X*2) => (X << 1)
// 6. Multiplies with a power-of-two constant argument are transformed into
// shifts.
// N. This list is incomplete
//
//===----------------------------------------------------------------------===//
@ -272,6 +275,11 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
if (RHS == Constant::getNullValue(I.getType()))
return ReplaceInstUsesWith(I, LHS);
// Convert 'add X, X' to 'shl X, 1'
if (LHS == RHS && I.getType()->isInteger())
return new ShiftInst(Instruction::Shl, LHS,
ConstantInt::get(Type::UByteTy, 1));
// -A + B --> B - A
if (Value *V = dyn_castNegVal(LHS))
return BinaryOperator::create(Instruction::Sub, RHS, V);
@ -390,6 +398,14 @@ Instruction *InstCombiner::visitMul(BinaryOperator &I) {
// Simplify mul instructions with a constant RHS...
if (Constant *Op1 = dyn_cast<Constant>(I.getOperand(1))) {
if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
// ((X << C1)*C2) == (X * (C2 << C1))
if (ShiftInst *SI = dyn_cast<ShiftInst>(Op0))
if (SI->getOpcode() == Instruction::Shl)
if (Constant *ShOp = dyn_cast<Constant>(SI->getOperand(1)))
return BinaryOperator::create(Instruction::Mul, SI->getOperand(0),
*CI << *ShOp);
const Type *Ty = CI->getType();
int64_t Val = (int64_t)cast<ConstantInt>(CI)->getRawValue();
switch (Val) {
@ -399,8 +415,6 @@ Instruction *InstCombiner::visitMul(BinaryOperator &I) {
return ReplaceInstUsesWith(I, Op1); // Eliminate 'mul double %X, 0'
case 1:
return ReplaceInstUsesWith(I, Op0); // Eliminate 'mul int %X, 1'
case 2: // Convert 'mul int %X, 2' to 'add int %X, %X'
return BinaryOperator::create(Instruction::Add, Op0, Op0, I.getName());
}
if (uint64_t C = Log2(Val)) // Replace X*(2^C) with X << C
@ -902,6 +916,14 @@ Instruction *InstCombiner::visitShiftInst(ShiftInst &I) {
(!Op0->getType()->isSigned() || isLeftShift))
return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType()));
// ((X*C1) << C2) == (X * (C1 << C2))
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op0))
if (BO->getOpcode() == Instruction::Mul && isLeftShift)
if (Constant *BOOp = dyn_cast<Constant>(BO->getOperand(1)))
return BinaryOperator::create(Instruction::Mul, BO->getOperand(0),
*BOOp << *CUI);
// If the operand is an bitwise operator with a constant RHS, and the
// shift is the only use, we can pull it out of the shift.
if (Op0->use_size() == 1)
@ -989,12 +1011,6 @@ Instruction *InstCombiner::visitShiftInst(ShiftInst &I) {
}
}
}
// Check to see if we are shifting left by 1. If so, turn it into an add
// instruction.
if (isLeftShift && CUI->equalsInt(1))
// Convert 'shl int %X, 1' to 'add int %X, %X'
return BinaryOperator::create(Instruction::Add, Op0, Op0, I.getName());
}
return 0;