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What are the ways compilers recognize complex patterns?
This answer is an example of a compiler recognizing that a complex expression is equivalent to a single operation: uint8_t pcnt64(uint64_t n) { n = n - ((n >> 1) & 0x5555555555555555...
I haven’t personally investigated the extent to which this is true, but the author cites Hacker’s Delight as the source of the pattern they’ve chosen to recognize. This means that, though the pattern being scanned for is fairly simple, there is good reason to believe minor variations in the way it’s written in the source code will all be normalized to the same basic shape, as long as they are fundamentally the same algorithm. In theory, a compiler could choose to implement a set of extremely sophisticated algorithms to squeeze every last drop of performance from a program, but this is not done in practice, for several reasons:
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