Improve optimization of select between same values#8806
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We previously optimized selects between the same value only when the ifTrue and ifFalse values had identical structure and no side effects and the condition could be dropped or reordered with the value. Make this more robust by using the `areConsecutiveInputs...` utilities to check whether the arms have equal values and whether they are foldable. The old code avoided introducing blocks to keep code size down, but the blocks it would introduce are not named and will be elided in the output, so introducing blocks is not a problem. The old code also avoided introducing a scratch local, but if a scratch local is necessary, it is because the arms have some side effects that would prevent reordering. In that case it is more likely to be beneficial to execute only one arm, so go ahead and use scratch locals in the case where the second arm can be folded away.
stevenfontanella
approved these changes
Jun 5, 2026
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We previously optimized selects between the same value only when the ifTrue and ifFalse values had identical structure and no side effects and the condition could be dropped or reordered with the value.
Make this more robust by using the
areConsecutiveInputs...utilities to check whether the arms have equal values and whether they are foldable. The old code avoided introducing blocks to keep code size down, but the blocks it would introduce are not named and will be elided in the output, so introducing blocks is not a problem. The old code also avoided introducing a scratch local, but if a scratch local is necessary, it is because the arms have some side effects that would prevent reordering. In that case it is more likely to be beneficial to execute only one arm, so go ahead and use scratch locals in the case where the second arm can be folded away.