[PATCH] D94089: [Reassociate] move check to ignore boolean expressions before canonicalizing binary operands

[Marius Hillenbrand via Phabricator via llvm-commits]

mhillenbrand added a comment.

@lebedev.ri No, I do not see differences in observable side-effects. Though, runtime differs significantly depending on the order of evaluation. Thus, "intent" would be out-of-band information that the programmer has about the likelihood of  each of the terms being true, and placing the most-likely term first, while that cannot be derived from the source by the compiler.

In the example

  if (ab > de || ac > df || bc > cd)
        return 0;

the programmer may know that (ab > de) is more commonly true than (ac >df) and thus place the former check first. With short-circuited evaluation strictly in the order of the source code, the resulting code would execute fewer comparisons and run faster, and vice versa.

@fhahn I will add a test (seeking feedback whether this actually makes sense with this initial submission).


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https://reviews.llvm.org/D94089