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cmd/compile: internal compiler error: esc return list involving constant groups and unsafe.Sizeof #20260

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josharian opened this Issue May 5, 2017 · 1 comment

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josharian commented May 5, 2017

package p

import "unsafe"

const (
	a = unsafe.Sizeof(func() int {
		return 0
	}())
	b
)
$ go tool compile x.go 
x.go:7:3: internal compiler error: esc return list

goroutine 1 [running]:
runtime/debug.Stack(0x0, 0x0, 0x0)
	/Users/josh/go/tip/src/runtime/debug/stack.go:24 +0xa7
cmd/compile/internal/gc.Fatalf(0x179c214, 0xf, 0x0, 0x0, 0x0)
	/Users/josh/go/tip/src/cmd/compile/internal/gc/subr.go:181 +0x230
cmd/compile/internal/gc.(*EscState).esc(0xc4200b8400, 0xc4202f7280, 0xc420316280)
	/Users/josh/go/tip/src/cmd/compile/internal/gc/esc.go:871 +0x127d
cmd/compile/internal/gc.(*EscState).esclist(0xc4200b8400, 0xc4202eff40, 0xc420316280)
	/Users/josh/go/tip/src/cmd/compile/internal/gc/esc.go:648 +0x6d
cmd/compile/internal/gc.(*EscState).escfunc(0xc4200b8400, 0xc420316280)
	/Users/josh/go/tip/src/cmd/compile/internal/gc/esc.go:589 +0x18c
cmd/compile/internal/gc.escAnalyze(0xc42000c5e0, 0x1, 0x1, 0xc42031e000)
	/Users/josh/go/tip/src/cmd/compile/internal/gc/esc.go:491 +0x566
cmd/compile/internal/gc.(*bottomUpVisitor).visit(0xc420333810, 0xc420316280, 0xc400000002)
	/Users/josh/go/tip/src/cmd/compile/internal/gc/esc.go:107 +0x25c
cmd/compile/internal/gc.visitBottomUp(0xc4202efd40, 0x4, 0x4, 0x17b2200)
	/Users/josh/go/tip/src/cmd/compile/internal/gc/esc.go:63 +0xeb
cmd/compile/internal/gc.escapes(0xc4202efd40, 0x4, 0x4)
	/Users/josh/go/tip/src/cmd/compile/internal/gc/esc.go:187 +0x4b
cmd/compile/internal/gc.Main(0x17b2080)
	/Users/josh/go/tip/src/cmd/compile/internal/gc/main.go:545 +0x2392
main.main()
	/Users/josh/go/tip/src/cmd/compile/main.go:49 +0x95

Found with go-fuzz. Low priority.

@josharian

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josharian commented May 5, 2017

Per #20262 and #12946, the bug here is that escape analysis is looking inside the function at all. The fix is probably to nil out the body of the function once typechecking has decided that we're working with unsafe.Sizeof and has determined the type of the return value.

@ALTree ALTree added the NeedsFix label Sep 22, 2018

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