cmd/compile: internal compiler error: unused auto: .autotmp_4

[ALTree]

$ gotip version
go version devel go1.22-d9a4b24a Thu Sep 7 15:25:07 2023 +0000 linux/amd64

package main

import "unsafe"

func F[G int](g G) uintptr {
	var c chan func() int
	type s struct {
		_ G
		_ []int
	}
	return unsafe.Sizeof(s{g, make([]int, (<-c)())})
}

func main() {
	F(0)
}

$ gotip build crash.go 

# command-line-arguments
./crash.go:11:45: internal compiler error: unused auto: .autotmp_4

goroutine 1 [running]:
runtime/debug.Stack()
	./desktop/gotip/src/runtime/debug/stack.go:24 +0x5e
cmd/compile/internal/base.FatalfAt({0xcfa3e0?, 0x0?}, {0xd6fb2e, 0xf}, {0xc000409468, 0x1, 0x1})
	./desktop/gotip/src/cmd/compile/internal/base/print.go:225 +0x1d7
cmd/compile/internal/inline.pruneUnusedAutos({0xc00040c6c0, 0x5, 0x1?}, 0xc00040cbc0)
	./desktop/gotip/src/cmd/compile/internal/inline/inl.go:1176 +0x185
cmd/compile/internal/inline.CanInline(0xc000412000, 0x0)
...

Doesn't crash on 1.21

cc @golang/compiler

[mauri870]

I was able to bisect the changes and CL 523315 seems to be the culprint.

[mauri870]

cc @mdempsky

[cuonglm]

This seems becasue make([]int, (<-c)()) is rewritten into:

var autotmp_4 func() int
autotmp_4 = <-c
return unsafe.Sizeof(s{g, make([]int, autotmp_4())})

Then when reading function body, unified IR eval the unsafe.Sizeof to just return 32, so autotmp_4 appears in F declaration list but is not recorded as used.

[gopherbot]

Change https://go.dev/cl/527097 mentions this issue: cmd/compile/internal/noder: handle unsafe.Sizeof, etc in unified IR