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cmd/compile: avoid dead code in escape analysis #16871

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dsnet opened this issue Aug 25, 2016 · 7 comments
Closed

cmd/compile: avoid dead code in escape analysis #16871

dsnet opened this issue Aug 25, 2016 · 7 comments
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@dsnet
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dsnet commented Aug 25, 2016

Using go1.7

Consider the following function:

func Foo(codes []int) int {
    const debug = false
    if debug && !sort.IntsAreSorted(codes) {
        panic("input slice is not sorted")
    }

    var s int
    for _, i := range codes {
        s += i
    }
    return s
}

Currently, codes escapes to the heap. I expect it to not escape since the function where it does escape sort.IntsAreSorted is dead. (the fact that codes escapes at all in sort.IntsAreSorted is a separate concern).

/cc @dr2chase
@dsnet dsnet added this to the Unplanned milestone Aug 25, 2016
@josharian
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Ordering the many compiler stages is a tricky problem. It'd also be nice for dead code not to count against a function's budget for inlining. It might be nice to add an early, crude deadcode pass, which implies also doing a bunch of constant folding. And we'd need to make sure all code gets typechecked, dead or not.

@navytux
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navytux commented Jan 31, 2017

Looks to be the same as #12397.

@minux
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minux commented Feb 1, 2017 via email

@dr2chase
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dr2chase commented Feb 1, 2017

Right now DCE is in SSA and SSA uses results of escape analysis, so that's moderately tricky. We would need an even-more-generic form of SSA that was (initially) agnostic about whether things were heap or stack allocated.

@minux
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minux commented Feb 1, 2017 via email

@randall77
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randall77 commented Feb 1, 2017 via email

@gopherbot
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CL https://golang.org/cl/37508 mentions this issue.

@golang golang locked and limited conversation to collaborators Feb 27, 2018
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@josharian @minux @navytux @dr2chase @dsnet @randall77 @gopherbot