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cmd/compile: "attempt to load unspilled value" compiling valid code #15084

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josharian opened this issue Apr 3, 2016 · 7 comments
Closed

cmd/compile: "attempt to load unspilled value" compiling valid code #15084

josharian opened this issue Apr 3, 2016 · 7 comments
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Go1.7

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@josharian
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Attempt to compile:

package x

type T struct {
    i int
    e interface{}
}

func (t *T) F() bool {
    if t.i != 0 {
        return false
    }
    _, ok := t.e.(string)
    return ok
}

var x int

func g(t *T) {
    if t.F() || true {
        if t.F() {
            x = 0
        }
    }
}

Result:

x.go:19: internal compiler error: attempt to load unspilled value v69 = MOVQload <*uint8> [8] v5 v1

git bisect points at 40f2b57, CL 19728.

This is blocking other compiler changes I'm working on.

cc @brtzsnr @dr2chase @randall77
@josharian josharian added this to the Go1.7 milestone Apr 3, 2016
@brtzsnr
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brtzsnr commented Apr 3, 2016

Looks like an issue in the register allocator and that cl is just triggering it. I don't know enough about the register allocator, so I cannot be sure.

@josharian
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May be, although it is also possible that this case tickles deadcode into feeding the register allocator invalid SSA. I haven't looked.

In any case, when this is fixed, we should also remove the go:noinline work around for IsSlice (in type.go) introduced in CL 21611.

@gopherbot
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CL https://golang.org/cl/22330 mentions this issue.

gopherbot pushed a commit that referenced this issue Apr 21, 2016
@randall77
cmd/compile: fix dominator check in check()
4938d7b 
Ancestor comparison was the wrong way around, effectively
disabling the def-must-dominate-use check.

Update #15084

Change-Id: Ic56d674c5000569d2cc855bbb000a60eae517c7c
Reviewed-on: https://go-review.googlesource.com/22330
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
@gopherbot
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CL https://golang.org/cl/22334 mentions this issue.

@randall77
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randall77 commented Apr 21, 2016 •
edited by bradfitz

Combination of:

  1. phielimValue leaving graph with values not dominating uses (https://go-review.googlesource.com/c/22335/)
  2. bug in the dominator graph calculation ( cl/22334 )
  3. bug in check() not detecting 1 or 2 ( cl/22330 )
    All in all, a very nice test case.

@dr2chase
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Should be fixed, see https://go-review.googlesource.com/#/c/22347/

@gopherbot
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CL https://golang.org/cl/22426 mentions this issue.

@golang golang locked and limited conversation to collaborators Apr 25, 2017
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@brtzsnr @josharian @dr2chase @randall77 @gopherbot