New MIR opt pass simplify_pow_of_two#114254
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Centri3 wants to merge 5 commits intorust-lang:masterfrom
Closed
New MIR opt pass simplify_pow_of_two#114254Centri3 wants to merge 5 commits intorust-lang:masterfrom
simplify_pow_of_two#114254Centri3 wants to merge 5 commits intorust-lang:masterfrom
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This detects calls to
x.powwherexis a power of two and an integer. This can use shl instead, with some nuances. Unfortunately modifyingpowinstead results in this check being done at runtime, and also getting the power used, thus is even slower than without it.Supersedes the clippy lint rust-lang/rust-clippy#11057
I haven't benchmarked this yet but from my testing, without debug assertions this has 0 branches, thus is branchless, and only has a couple instructions, so I'm 99% confident this is faster. With debug assertions, I'm not sure,
custom_mirdoesn't really like assertions 😅For calls where
xis not 2, the rhs for shl can beexp * <power used to get x>.Hope I did everything right ^^