cmd/compile: panic running code that uses generic interface value

[apmckinlay]

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

$ go version
go version go1.18rc1 darwin/amd64

Does this issue reproduce with the latest release?

gotip playground also fails

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/andrew/Library/Caches/go-build"
GOENV="/Users/andrew/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/andrew/Go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/andrew/Go:/Users/andrew/Dropbox/suneido_tests"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/Users/andrew/sdk/go1.18rc1"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/Users/andrew/sdk/go1.18rc1/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.18rc1"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/andrew/Dropbox/gsuneido18/go.mod"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/dc/0y3gfqnn56g6pd8d3_b5wz300000gn/T/go-build1447860490=/tmp/go-build -gno-record-gcc-switches -fno-common"
GOROOT/bin/go version: go version go1.17.7 darwin/amd64
GOROOT/bin/go tool compile -V: compile version go1.18rc1
uname -v: Darwin Kernel Version 21.3.0: Wed Jan  5 21:37:58 PST 2022; root:xnu-8019.80.24~20/RELEASE_X86_64
ProductName:	macOS
ProductVersion:	12.2.1
BuildVersion:	21D62
lldb --version: lldb-1205.0.27.3
Apple Swift version 5.4 (swiftlang-1205.0.26.9 clang-1205.0.19.55)

What did you do?

https://gotipplay.golang.org/p/Gg7oSlfPoHI

What did you expect to see?

no error

What did you see instead?

It appears to fail on: if x.Equal(xe, ye) {
Although if you comment out the following append line, then it passes.

In the gotip playground it gives:

panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x4b1501]

On my Mac it gives:

runtime: unexpected return pc for runtime.sigpanic

=== RUN   TestIntersectSS
xe [1]
ye [2 3]
x [[1]]
runtime: unexpected return pc for runtime.sigpanic called from 0x1127eda
stack: frame={sp:0xc00007cd80, fp:0xc00007cdd0} stack=[0xc00007c000,0xc00007d000)
0x000000c00007cc80:  0x000000c00007cc88  0x0000000001032580 
0x000000c00007cc90:  0x0000000001047c76   0x000000c00007cd80
0x000000c00007cca0:  0x000000c000138340  0x0000000000000000
0x000000c00007ccb0:  0x000000c00007cd70  0x0000000001032d46 
0x000000c00007ccc0:  0x0000000000000001  0x0000000001101da0
0x000000c00007ccd0:  0x000000c000104078  0x000000c0000240a0
0x000000c00007cce0:  0x0000000000000000  0x0000000000000000
0x000000c00007ccf0:  0x000000000107d6c0   0x000000c000104060
0x000000c00007cd00:  0x000000c00007ccf0  0x000000c00007cd70
0x000000c00007cd10:  0x0000000001068b5e   0x000000c000104060
0x000000c00007cd20:  0x000000c00007cd48  0x000000c000138360
0x000000c00007cd30:  0x000000c000138340  0x0000000000000000
0x000000c00007cd40:  0x0000000001102ac0  0x00000000011f2ca0
0x000000c00007cd50:  0x0000000000000000  0x0000000000000000
0x000000c00007cd60:  0x0000000000000000  0x0000000000000000
0x000000c00007cd70:  0x000000c00007cdc0  0x0000000001047c76 
0x000000c00007cd80: <0x0000000001102ac0  0x00000000011f2ca0
0x000000c00007cd90:  0x0000000000000008  0x000000c00007cdc0
0x000000c00007cda0:  0x0000000000000008  0x000000c000103110
0x000000c00007cdb0:  0x0000000000000000  0x0000000000000000
0x000000c00007cdc0:  0x000000c00007cef8 !0x0000000001127eda
0x000000c00007cdd0: >0x0000000001149620  0x000000c00000e018
0x000000c00007cde0:  0x000000c00007ce98  0x0000000000000002
0x000000c00007cdf0:  0x0000000000000002  0x0000000000000000
0x000000c00007ce00:  0x00000000010b2a80   0x00000000011d40c8
0x000000c00007ce10:  0x0000000000000000  0x0000000000000000
0x000000c00007ce20:  0x0000000000000002  0x0000000000000002
0x000000c00007ce30:  0x0000000000000001  0x0000000000000001
0x000000c00007ce40:  0x0000000000000000  0x0000000000000000
0x000000c00007ce50:  0x0000000000000000  0x000000c0000162c0
0x000000c00007ce60:  0x000000c0000162b8  0x000000c00007cf48
0x000000c00007ce70:  0x000000c00000c090  0x000000c00000c090
0x000000c00007ce80:  0x000000c000088f10  0x0000000000000001
0x000000c00007ce90:  0x0000000000000001  0x00000000010fcd00
0x000000c00007cea0:  0x0000000001148d80  0x0000000001101da0
0x000000c00007ceb0:  0x000000c00000c0d8  0x00000000010fcd00
0x000000c00007cec0:  0x0000000001148d70  0x00000000010fab00
fatal error: unknown caller pc
runtime stack:

runtime.throw({0x111ff47?, 0x11e4180?})

/Users/andrew/sdk/go1.18rc1/src/runtime/panic.go:992 +0x71

runtime.gentraceback(0xc000138340?, 0x10648df?, 0xc00007cbe8?, 0x11fbde0?, 0x0, 0x0, 0x7fffffff, 0x7ff7bfeff468, 0x20?, 0x0)

/Users/andrew/sdk/go1.18rc1/src/runtime/traceback.go:254 +0x1a36

runtime.addOneOpenDeferFrame.func1()

/Users/andrew/sdk/go1.18rc1/src/runtime/panic.go:599 +0x6b

runtime.systemstack()

/Users/andrew/sdk/go1.18rc1/src/runtime/asm_amd64.s:469 +0x49
goroutine 4 [running]:

runtime.systemstack_switch()

/Users/andrew/sdk/go1.18rc1/src/runtime/asm_amd64.s:436 fp=0xc00007cc80 sp=0xc00007cc78 pc=0x1060880

runtime.addOneOpenDeferFrame(0x1?, 0x1101da0?, 0xc000104078?)

/Users/andrew/sdk/go1.18rc1/src/runtime/panic.go:598 +0x69 fp=0xc00007ccc0 sp=0xc00007cc80 pc=0x1032529

panic({0x1102ac0, 0x11f2ca0})

/Users/andrew/sdk/go1.18rc1/src/runtime/panic.go:798 +0x106 fp=0xc00007cd80 sp=0xc00007ccc0 pc=0x1032d46

runtime: unexpected return pc for runtime.sigpanic called from 0x1127eda

stack: frame={sp:0xc00007cd80, fp:0xc00007cdd0} stack=[0xc00007c000,0xc00007d000)

0x000000c00007cc80:  0x000000c00007cc88  0x0000000001032580 <runtime.addOneOpenDeferFrame.func1+0x0000000000000000>

0x000000c00007cc90:  0x0000000001047c76 <runtime.sigpanic+0x0000000000000336>  0x000000c00007cd80

0x000000c00007cca0:  0x000000c000138340  0x0000000000000000

0x000000c00007ccb0:  0x000000c00007cd70  0x0000000001032d46 <runtime.gopanic+0x0000000000000106>

0x000000c00007ccc0:  0x0000000000000001  0x0000000001101da0

0x000000c00007ccd0:  0x000000c000104078  0x000000c0000240a0

0x000000c00007cce0:  0x0000000000000000  0x0000000000000000

0x000000c00007ccf0:  0x000000000107d6c0 <internal/poll.(*FD).Write.func1+0x0000000000000000>  0x000000c000104060

0x000000c00007cd00:  0x000000c00007ccf0  0x000000c00007cd70

0x000000c00007cd10:  0x0000000001068b5e <sync.(*Pool).pin+0x000000000000001e>  0x000000c000104060

0x000000c00007cd20:  0x000000c00007cd48  0x000000c000138360

0x000000c00007cd30:  0x000000c000138340  0x0000000000000000

0x000000c00007cd40:  0x0000000001102ac0  0x00000000011f2ca0

0x000000c00007cd50:  0x0000000000000000  0x0000000000000000

0x000000c00007cd60:  0x0000000000000000  0x0000000000000000

0x000000c00007cd70:  0x000000c00007cdc0  0x0000000001047c76 <runtime.sigpanic+0x0000000000000336>

0x000000c00007cd80: <0x0000000001102ac0  0x00000000011f2ca0

0x000000c00007cd90:  0x0000000000000008  0x000000c00007cdc0

0x000000c00007cda0:  0x0000000000000008  0x000000c000103110

0x000000c00007cdb0:  0x0000000000000000  0x0000000000000000

0x000000c00007cdc0:  0x000000c00007cef8 !0x0000000001127eda

0x000000c00007cdd0: >0x0000000001149620  0x000000c00000e018

0x000000c00007cde0:  0x000000c00007ce98  0x0000000000000002

0x000000c00007cdf0:  0x0000000000000002  0x0000000000000000

0x000000c00007ce00:  0x00000000010b2a80 <testing.tRunner+0x0000000000000000>  0x00000000011d40c8

0x000000c00007ce10:  0x0000000000000000  0x0000000000000000

0x000000c00007ce20:  0x0000000000000002  0x0000000000000002

0x000000c00007ce30:  0x0000000000000001  0x0000000000000001

0x000000c00007ce40:  0x0000000000000000  0x0000000000000000

0x000000c00007ce50:  0x0000000000000000  0x000000c0000162c0

0x000000c00007ce60:  0x000000c0000162b8  0x000000c00007cf48

0x000000c00007ce70:  0x000000c00000c090  0x000000c00000c090

0x000000c00007ce80:  0x000000c000088f10  0x0000000000000001

0x000000c00007ce90:  0x0000000000000001  0x00000000010fcd00

0x000000c00007cea0:  0x0000000001148d80  0x0000000001101da0

0x000000c00007ceb0:  0x000000c00000c0d8  0x00000000010fcd00

0x000000c00007cec0:  0x0000000001148d70  0x00000000010fab00

runtime.panicmem(...)

/Users/andrew/sdk/go1.18rc1/src/runtime/panic.go:220

runtime.sigpanic()

/Users/andrew/sdk/go1.18rc1/src/runtime/signal_unix.go:818 +0x336 fp=0xc00007cdd0 sp=0xc00007cd80 pc=0x1047c76

created by testing.(*T).Run

/Users/andrew/sdk/go1.18rc1/src/testing/testing.go:1486 +0x35f
goroutine 1 [chan receive]:

testing.(*T).Run(0xc000138000, {0x111f5f4?, 0xa93fd983ba5?}, 0x1127d00)

/Users/andrew/sdk/go1.18rc1/src/testing/testing.go:1487 +0x37a

testing.runTests.func1(0xc000100450?)

/Users/andrew/sdk/go1.18rc1/src/testing/testing.go:1839 +0x6e

testing.tRunner(0xc000138000, 0xc000131cd8)

/Users/andrew/sdk/go1.18rc1/src/testing/testing.go:1439 +0x102

testing.runTests(0xc000116140?, {0x11f2f40, 0x1, 0x1}, {0x128c108?, 0x40?, 0x11fb6e0?})

/Users/andrew/sdk/go1.18rc1/src/testing/testing.go:1837 +0x457

testing.(*M).Run(0xc000116140)

/Users/andrew/sdk/go1.18rc1/src/testing/testing.go:1719 +0x5d9

main.main()

_testmain.go:47 +0x1aa

FAIL	github.com/apmckinlay/gsuneido/util/generic/bug	0.352s

[ianlancetaylor]

At first glance this does seem to be a bug in the dictionary code somewhere.

CC @randall77 @danscales

[danscales]

This is an interesting issue. I haven't totally figured out all the details, but it relates to the way we create shape types for instantiations. The complex case here is when we already have a shape type, then we construct a new compound type from that that shape, and we end up using that as a type arg to another generic function. I think we're not always handling things correctly in the case where the type arg has a shape type in it, but is not a top-level shape type (i.e. we have a shape type S, and compound type arg we are passing to another generic function is []S).

[danscales]

I have a rough fix. Will need to think on it a bit more and discuss with @randall77 .

[gopherbot]

Change https://go.dev/cl/387674 mentions this issue: cmd/compile: deal with constructed types that have shapes in them

[danscales]

Keith and I are still discussing the most complete way to fix this.

[danscales]

I have submitted my fix, after discussion with Keith and some extra prototyping. This issue still needs to be investigated for Go 1.19 (best way to deal with these types created from shape types), but removing it from release blocker.

[apmckinlay]

Sounds good, thanks.