cmd/compile: ICE on slice of array pointer returned by a generic function

[mcy]

Go version

go version go1.23.0 darwin/arm64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/mcyoung/Library/Caches/go-build'
GOENV='/Users/mcyoung/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/mcyoung/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/mcyoung/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/opt/homebrew/Cellar/go/1.23.0/libexec'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='local'
GOTOOLDIR='/opt/homebrew/Cellar/go/1.23.0/libexec/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.23.0'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/mcyoung/Library/Application Support/go/telemetry'
GCCGO='gccgo'
GOARM64='v8.0'
AR='ar'
CC='cc'
CXX='c++'
CGO_ENABLED='1'
GOMOD='/Users/mcyoung/code/protocompile/go.mod'
GOWORK='/Users/mcyoung/code/protocompile/go.work'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/5l/2_ns6hbx1gj92vv9pkrl_jdc0000gn/T/go-build656695524=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

The following program crashes the compiler:

package x

func F[T int32]() {
	_ = G[*[0]T]()[:]
}

func G[T any]() (v T) {
	return
}

var _ = F[int32]

I have not been able to reduce this program further: everything, except the body of G, is essential to triggering the bug. F must be stenciled, G must return a generic type, not *T or *[0]T, and the type constraint on F[T] seems to be irrelevant.

What did you see happen?

ICE.

./prog.go:3:6: internal compiler error: 'F[int32]': bad ptr to array in slice go.shape.*uint8


Please file a bug report including a short program that triggers the error.
https://go.dev/issue/new

What did you expect to see?

Not an ICE.

[mauri870]

In gotip I get a more verbose error:

# command-line-arguments
./test.go:3:6: internal compiler error: 'F[int32]': bad ptr to array in slice go.shape.*uint8


./test.go:4:16: internal compiler error: 'F[go.shape.int32]': bad ptr to array in slice go.shape.*uint8


goroutine 9 [running]:
runtime/debug.Stack()
        ./src/runtime/debug/stack.go:26 +0x5e
cmd/compile/internal/base.FatalfAt({0x47aea0?, 0xc0?}, {0xc000027320, 0x23}, {0xc00046c360, 0x2, 0x2})
        ./src/cmd/compile/internal/base/print.go:230 +0x1ea
cmd/compile/internal/base.Fatalf(...)
        ./src/cmd/compile/internal/base/print.go:195
cmd/compile/internal/ssagen.(*ssafn).Fatalf(0x0?, {0x46e260?, 0xc0?}, {0xec7884, 0x1d}, {0xc00046e260, 0x1, 0x1?})
        ./src/cmd/compile/internal/ssagen/ssa.go:7341 +0x171
cmd/compile/internal/ssagen.(*state).Fatalf(0xc00045c8f0?, {0xec7884?, 0xc000040a00?}, {0xc00046e260?, 0xc0004661a0?, 0x0?})
        ./src/cmd/compile/internal/ssagen/ssa.go:965 +0x64
cmd/compile/internal/ssagen.(*state).slice(0xc000040a00, 0xc000568c70, 0x0, 0x0, 0x0, 0x0)
        ./src/cmd/compile/internal/ssagen/ssa.go:5194 +0x35a
cmd/compile/internal/ssagen.(*state).exprCheckPtr(0xc000040a00, {0x1037310, 0xc000465600}, 0x1)
        ./src/cmd/compile/internal/ssagen/ssa.go:3411 +0x564e
cmd/compile/internal/ssagen.(*state).expr(...)
        ./src/cmd/compile/internal/ssagen/ssa.go:2783
cmd/compile/internal/ssagen.(*state).stmt(0xc000040a00, {0x1037a18, 0xc000462780})
        ./src/cmd/compile/internal/ssagen/ssa.go:1682 +0x7065
cmd/compile/internal/ssagen.(*state).stmtList(...)
        ./src/cmd/compile/internal/ssagen/ssa.go:1449
cmd/compile/internal/ssagen.buildssa(0xc00043da40, 0x3, 0x0)
        ./src/cmd/compile/internal/ssagen/ssa.go:580 +0x2aa5
cmd/compile/internal/ssagen.Compile(0xc00043da40, 0x3, 0xc00009c788?)
        ./src/cmd/compile/internal/ssagen/pgen.go:304 +0x88
cmd/compile/internal/gc.compileFunctions.func5.1(0x455232?)
        ./src/cmd/compile/internal/gc/compile.go:189 +0x38
cmd/compile/internal/gc.compileFunctions.func3.1()
        ./src/cmd/compile/internal/gc/compile.go:171 +0x30
created by cmd/compile/internal/gc.compileFunctions.func3 in goroutine 8
        ./src/cmd/compile/internal/gc/compile.go:170 +0x247

cc @randall77

[prattmic]

cc @golang/compiler

[gopherbot]

Change https://go.dev/cl/641955 mentions this issue: cmd/compile: do not shapify a pointer-shaping