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[turbofan] Avoid expensive fixup for Uint32Div if divisor is even.

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R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/840813008

Cr-Commit-Position: refs/heads/master@{#26036}
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bmeurer 2015-01-13 02:01:06 -08:00 committed by Commit bot
parent bcab9eacf3
commit ca741a0b3c
1 changed files with 7 additions and 1 deletions
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8
src/compiler/machine-operator-reducer.cc
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@ -104,8 +104,14 @@ Node* MachineOperatorReducer::Int32Div(Node* dividend, int32_t divisor) {
Node* MachineOperatorReducer::Uint32Div(Node* dividend, uint32_t divisor) {
DCHECK_LT(0, divisor);
// If the divisor is even, we can avoid using the expensive fixup by shifting
// the dividend upfront.
unsigned const shift = base::bits::CountTrailingZeros32(divisor);
dividend = Word32Shr(dividend, shift);
divisor >>= shift;
// Compute the magic number for the (shifted) divisor.
base::MagicNumbersForDivision<uint32_t> const mag =
base::UnsignedDivisionByConstant(bit_cast<uint32_t>(divisor));
base::UnsignedDivisionByConstant(divisor, shift);
Node* quotient = graph()->NewNode(machine()->Uint32MulHigh(), dividend,
Uint32Constant(mag.multiplier));
if (mag.add) {