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openedon Nov 9, 2019
The ?
operator is not zero cost right now, because the matches generated by it don't get optimized as well as they could.
I see
_3 = ((_1 as Ok).0: u32);
_4 = _3;
((_0 as Ok).0: u32) = move _4;
discriminant(_0) = 0;
and
_5 = ((_1 as Err).0: i32);
_6 = _5;
((_0 as Err).0: i32) = move _6;
discriminant(_0) = 1;
Which we could reasonably write a peephole optimization for getting transformed to
_0 = _1
each
Then a second optimization could find switchInt
terminators where all basic blocks are the same and eliminate the switchInt
by replacing it to a goto to the first basic block being switched to.
This will even benefit matches where only one arm is a nop, because that arm will just become a memcopy
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Area: Mid-level IR (MIR) - https://blog.rust-lang.org/2016/04/19/MIR.htmlArea: Code generationArea: MIR optimizationsArea: MIR inliningCategory: An issue proposing an enhancement or a PR with one.Category: An issue highlighting optimization opportunities or PRs implementing suchIssue: Problems and improvements with respect to performance of generated code.Relevant to the compiler team, which will review and decide on the PR/issue.