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cmd/compile: infinite loop in types2 #48136

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@reusee

Description

@reusee

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

$ go version
go version devel go1.18-df4c625d88 Thu Sep 2 01:06:17 2021 +0000 windows/amd64

Does this issue reproduce with the latest release?

No

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

go env Output
$ go env
set GO111MODULE=
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\reus\AppData\Local\go-build
set GOENV=C:\Users\reus\AppData\Roaming\go\env
set GOEXE=.exe
set GOEXPERIMENT=
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GOMODCACHE=C:\Users\reus\go\pkg\mod
set GONOPROXY=github.com/reusee/*
set GONOSUMDB=github.com/reusee/*
set GOOS=windows
set GOPATH=C:\Users\reus\go
set GOPRIVATE=github.com/reusee/*
set GOPROXY=https://goproxy.cn,direct
set GOROOT=C:\Users\reus\gotip
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLDIR=C:\Users\reus\gotip\pkg\tool\windows_amd64
set GOVCS=
set GOVERSION=devel go1.18-df4c625d88 Thu Sep 2 01:06:17 2021 +0000
set GCCGO=gccgo
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=NUL
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\reus\AppData\Local\Temp\go-build2732815147=/tmp/go-build -gno-record-gcc-switches
GOROOT/bin/go version: go version devel go1.18-df4c625d88 Thu Sep 2 01:06:17 2021 +0000 windows/amd64
GOROOT/bin/go tool compile -V: compile version devel go1.18-df4c625d88 Thu Sep 2 01:06:17 2021 +0000

What did you do?

go build

package main

func Foo[
        Src interface {
                func() Src
        },
]() Src {
        return Foo[Src]
}

func main() {
  Foo()
}

What did you expect to see?

Compile OK

What did you see instead?

# command-line-arguments
runtime: goroutine stack exceeds 1000000000-byte limit
runtime: sp=0xc01ce01528 stack=[0xc01ce00000, 0xc03ce00000]
fatal error: stack overflow

runtime stack:
runtime.throw({0x143863c, 0x1a3afc0})
        C:/Users/reus/gotip/src/runtime/panic.go:965 +0x76
runtime.newstack()
        C:/Users/reus/gotip/src/runtime/stack.go:1085 +0x5cc
runtime.morestack()
        C:/Users/reus/gotip/src/runtime/asm_amd64.s:422 +0x93

goroutine 1 [running]:
cmd/compile/internal/types2.(*subster).typ(0xc03cdfde18, {0x1598640, 0xc004cc2a00})
        C:/Users/reus/gotip/src/cmd/compile/internal/types2/subst.go:87 +0x19e5 fp=0xc01ce01538 sp=0xc01ce01530 pc=0x12ac0c5
cmd/compile/internal/types2.(*subster).var_(0xc00ce017e8, 0xc004cc19e0)
        C:/Users/reus/gotip/src/cmd/compile/internal/types2/subst.go:297 +0x32 fp=0xc01ce01578 sp=0xc01ce01538 pc=0x12ac432
cmd/compile/internal/types2.(*subster).varList(0x0, {0xc004cb2a98, 0x1, 0x0})
        C:/Users/reus/gotip/src/cmd/compile/internal/types2/subst.go:318 +0x90 fp=0xc01ce015e8 sp=0xc01ce01578 pc=0x12ac690
cmd/compile/internal/types2.(*subster).tuple(0xc0085fde18, 0xc004cbb248)
        C:/Users/reus/gotip/src/cmd/compile/internal/types2/subst.go:308 +0x35 fp=0xc01ce01630 sp=0xc01ce015e8 pc=0x12ac555
cmd/compile/internal/types2.(*subster).typ(0xc03cdfde18, {0x1598640, 0xc004cc2a40})
        C:/Users/reus/gotip/src/cmd/compile/internal/types2/subst.go:127 +0x5df fp=0xc01ce01898 sp=0xc01ce01630 pc=0x12aacbf
cmd/compile/internal/types2.(*subster).var_(0xc00ce01b48, 0xc004cc1a40)
        C:/Users/reus/gotip/src/cmd/compile/internal/types2/subst.go:297 +0x32 fp=0xc01ce018d8 sp=0xc01ce01898 pc=0x12ac432
cmd/compile/internal/types2.(*subster).varList(0x0, {0xc004cb2aa0, 0x1, 0x0})
        C:/Users/reus/gotip/src/cmd/compile/internal/types2/subst.go:318 +0x90 fp=0xc01ce01948 sp=0xc01ce018d8 pc=0x12ac690
cmd/compile/internal/types2.(*subster).tuple(0xc0085fde18, 0xc004cbb260)

Activity

deleted a comment from gopherbot on Sep 2, 2021
danscales

danscales commented on Sep 2, 2021

@danscales
Contributor

Infinite loop in types2 substituter. @griesemer

changed the title [-]cmd/compile: infinite loop in both -G=3 and unified mode[/-] [+]cmd/compile: infinite loop in types2[/+] on Sep 2, 2021
added
NeedsFixThe path to resolution is known, but the work has not been done.
on Sep 2, 2021
added this to the Go1.18 milestone on Sep 2, 2021
findleyr

findleyr commented on Sep 2, 2021

@findleyr
Member

Related: #45550 and #48098.

Compile OK

FWIW, I don't think this function can reasonably compile without errors. What is the type of Foo()? We'd need a type name to define this kind of recursive data type (e.g. https://play.golang.org/p/JMlAom-VMOt).

self-assigned this
on Sep 2, 2021
added
NeedsInvestigationSomeone must examine and confirm this is a valid issue and not a duplicate of an existing one.
on Sep 2, 2021
griesemer

griesemer commented on Sep 2, 2021

@griesemer
Contributor

Nice! Thanks for reporting @reusee .

griesemer

griesemer commented on Sep 2, 2021

@griesemer
Contributor

Simpler reproducer:

package p

func f[P interface { *P }]() {}

func _() {
        f()
}
removed
NeedsFixThe path to resolution is known, but the work has not been done.
on Sep 2, 2021
griesemer

griesemer commented on Sep 2, 2021

@griesemer
Contributor

The issue here is that constraint type inference tries to unify P and *P which then leads to an infinite expansion loop (P = *P, P = **P, etc.). The fix requires detection of arbitrary cycles from (all) inferred types trough (all) type parameters. CL forthcoming.

added
NeedsFixThe path to resolution is known, but the work has not been done.
and removed
NeedsInvestigationSomeone must examine and confirm this is a valid issue and not a duplicate of an existing one.
on Sep 2, 2021

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        Issue actions

          cmd/compile: infinite loop in types2 · Issue #48136 · golang/go