alt Hacker NewsThat's what I would have thought as well, but looks like that on x86, both clang and gcc use variations of LEA. But if they're doing it this way, I'm pretty sure it must be faster, because even if you change the ×4 for a <<2, it will still generate a LEA.
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adrian_b • yesterday at 10:41 PM
They use LEA for multiplying with small constants up to 9 (not only with powers of two, but also with 3, 5 and 9; even more values could be achieved with two LEA, but it may not be worthwhile).
For multiplying with powers of two greater or equal to 16, they use shift left, because LEA can no longer be used.
Not only is LEA more flexible I believe it's preferred to SHL even for simple operations because it doesn't modify the flags register which can make it easier to schedule.