[CodeGen] Avoid quadratic operand removal in MachineInstr::insert - #220165
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No AI tools were used for this contribution. @arsenm Would you mind taking a look at this? Thanks! |
| for (unsigned I = OpIdx; I < NumOperands; ++I) { | ||
| MovingOps.emplace_back(getOperand(I)); | ||
| } | ||
| while (getNumOperands() != OpIdx) { | ||
| removeOperand(getNumOperands() - 1); | ||
| } |
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| MovingOps.emplace_back(getOperand(I)); | ||
| } | ||
| while (getNumOperands() != OpIdx) { | ||
| removeOperand(getNumOperands() - 1); |
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InsertBefore and operands_end() are MachineOperand * iterators, so you can initialize MovingOps directly with the iterator range constructor rather than manually looping with emplace_back.
This allows simplifying lines 2736–2748 to:
unsigned OpIdx = getOperandNo(InsertBefore);
SmallVector<MachineOperand> MovingOps(InsertBefore, operands_end());
while (getNumOperands() > OpIdx)
removeOperand(getNumOperands() - 1);(This also lets you eliminate NumOperands and OpsToMove above).
What's "MR?" |
GItlab speak for merge request |
| while (getNumOperands() != OpIdx) { | ||
| removeOperand(getNumOperands() - 1); | ||
| } |
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perhaps
for (unsigned I = getNumOperands(); I > OpIdx; --I)
removeOperand(I - 1);
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Thanks for the reviews! I've updated the patch. |
nickdesaulniers
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The commit body is currently empty. Consider putting something in there, such as matching the PR's description (modulo the MR term).
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…vm#220165) This optimizes MachineInstr::insert by copying trailing operands first and then removing them from the end. This avoids repeatedly shifting the remaining operands, reducing the operation from quadratic to linear time without changing behavior.
4 participants
This MR optimizes MachineInstr::insert by copying trailing operands first and then removing them from the end. This avoids repeatedly shifting the remaining operands, reducing the operation from quadratic to linear time without changing behavior.