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cmd/compile: walkConvInterface produces broken IR #56768

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cuonglm opened this issue Nov 16, 2022 · 3 comments
Closed

cmd/compile: walkConvInterface produces broken IR #56768

cuonglm opened this issue Nov 16, 2022 · 3 comments
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compiler/runtime Issues related to the Go compiler and/or runtime. FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done.
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@cuonglm
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cuonglm commented Nov 16, 2022

What version of Go are you using (go version)?

$ go version
go version devel go1.20-b1678e508b Wed Nov 16 04:04:52 2022 +0000 linux/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output
$ go env

What did you do?

Compile following program:

package p

type I interface {
	M()
}

type S struct{}

func (*S) M() {}

type slice []any

func f() {
	ss := struct {
		i I
	}{
		i: &S{},
	}

	_ = [...]struct {
		s slice
	}{
		{
			s: slice{ss.i},
		},
		{
			s: slice{ss.i},
		},
		{
			s: slice{ss.i},
		},
		{
			s: slice{ss.i},
		},
		{
			s: slice{ss.i},
		},
	}
}

What did you expect to see?

Compile ok.

What did you see instead?

/home/cuonglm/p.go:30:15: cannot use <node ITAB> (type *uintptr) as type *uint8 in assignment
/home/cuonglm/p.go:33:15: cannot use <node ITAB> (type *uintptr) as type *uint8 in assignment
/home/cuonglm/p.go:36:15: cannot use <node ITAB> (type *uintptr) as type *uint8 in assignment
/home/cuonglm/p.go:39:15: cannot use <node ITAB> (type *uintptr) as type *uint8 in assignment
/home/cuonglm/p.go:42:15: cannot use <node ITAB> (type *uintptr) as type *uint8 in assignment

The fix for #56727 reveals this bug, because it called typecheck on walked IR.

The problem is in walkConvInterface, we generate code like:

var typeWord *uint8
typeWord = itab

But itab has type *uintptr. I think we can just switch itab to *uint8 (any generic pointer type should work, I guess) cc @randall77

@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Nov 16, 2022
@cuonglm cuonglm self-assigned this Nov 16, 2022
@cuonglm cuonglm added this to the Go1.20 milestone Nov 16, 2022
@cuonglm cuonglm added the NeedsFix The path to resolution is known, but the work has not been done. label Nov 16, 2022
@gopherbot
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Change https://go.dev/cl/451256 mentions this issue: cmd/compile: fix broken IR for iface -> eface

@cuonglm
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cuonglm commented Nov 16, 2022

@gopherbot please backport this to go1.19

@gopherbot
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Backport issue(s) opened: #56770 (for 1.19).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://go.dev/wiki/MinorReleases.

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