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cmd/compile: missed constant folding #14363

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brtzsnr opened this issue Feb 17, 2016 · 2 comments
Closed

cmd/compile: missed constant folding #14363

brtzsnr opened this issue Feb 17, 2016 · 2 comments
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FrozenDueToAge Performance
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Go1.7

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@brtzsnr
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brtzsnr commented Feb 17, 2016

dev.ssa branch.

The compiler doesn't detect that v24 is a copy of v23 in the following case.
v23 = Or64 v19 v22
v24 = Or64 v19 v23

The compiler doesn't detect that v24 is a copy of v22 in the following case.
v23 = Xor64 v12 v22
v24 = Xor64 v12 v23

Not sure if we care about them or if they can be done (in a more general case) using rewrite rules only.
@randall77
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(or x (or x y)) -> (or x y) seems like a simple rewrite rule to capture this case.

In general, I'm not too worried about such cases. They tend not to happen much in user's code (except maybe generated code?) and the compiler doesn't introduce them as part of other phases.

@bradfitz bradfitz added this to the Go1.7 milestone Apr 10, 2016
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CL https://golang.org/cl/22188 mentions this issue.

@golang golang locked and limited conversation to collaborators Apr 18, 2017
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