cmd/compile/internal/SSA: panic in Compile on linux-amd64-noopt

[bcmills]

greplogs -l -e 'goroutine \d+ \[running\]:\nruntime\.throw(?:.+\n\t.+\n)*cmd/compile/internal/ssa\.Compile' --since=2022-01-01
2022-08-19T19:39:48-9a1d3b0/linux-amd64-noopt

goroutine 1 [running]:
runtime.throw({0x11a6896?, 0x10?})
	/workdir/go/src/runtime/panic.go:1047 +0x5d fp=0xc00048cf68 sp=0xc00048cf38 pc=0x43cd7d
runtime.sigpanic()
	/workdir/go/src/runtime/signal_unix.go:844 +0x1ca fp=0xc00048cf98 sp=0xc00048cf68 pc=0x453faa
math/rand.(*Rand).Int63(0xc00074e660)
	/workdir/go/src/math/rand/rand.go:84 +0x38 fp=0xc00048cfc0 sp=0xc00048cf98 pc=0x5ea1b8
math/rand.(*Rand).Int31(0xc00074e660)
	/workdir/go/src/math/rand/rand.go:98 +0x2b fp=0xc00048cfe8 sp=0xc00048cfc0 pc=0x5ea32b
math/rand.(*Rand).Int31n(0xc00074e660, 0x2f)
	/workdir/go/src/math/rand/rand.go:133 +0x93 fp=0xc00048d018 sp=0xc00048cfe8 pc=0x5ea5b3
math/rand.(*Rand).Intn(0xc00074e660, 0x2f)
	/workdir/go/src/math/rand/rand.go:171 +0x53 fp=0xc00048d050 sp=0xc00048d018 pc=0x5ea7b3
cmd/compile/internal/ssa.Compile(0xc000583520)
	/workdir/go/src/cmd/compile/internal/ssa/compile.go:91 +0x14f0 fp=0xc000490fd8 sp=0xc00048d050 pc=0x8acdb0
cmd/compile/internal/ssagen.buildssa(0xc000567cc0, 0x0)
	/workdir/go/src/cmd/compile/internal/ssagen/ssa.go:573 +0x224a fp=0xc0004917b0 sp=0xc000490fd8 pc=0xe2f5aa
cmd/compile/internal/ssagen.Compile(0xc000567cc0, 0x0)
	/workdir/go/src/cmd/compile/internal/ssagen/pgen.go:183 +0x3e fp=0xc000491928 sp=0xc0004917b0 pc=0xe2513e
cmd/compile/internal/gc.compileFunctions.func4.1(0x0)
	/workdir/go/src/cmd/compile/internal/gc/compile.go:153 +0x47 fp=0xc000491980 sp=0xc000491928 pc=0x10aad87
cmd/compile/internal/gc.compileFunctions.func2(0xc00074c0a0)
	/workdir/go/src/cmd/compile/internal/gc/compile.go:125 +0x23 fp=0xc000491998 sp=0xc000491980 pc=0x10b0ce3
cmd/compile/internal/gc.compileFunctions.func4({0xc0000f9e00, 0x37, 0x40})
	/workdir/go/src/cmd/compile/internal/gc/compile.go:152 +0x17b fp=0xc000491a18 sp=0xc000491998 pc=0x10aacdb
cmd/compile/internal/gc.compileFunctions()
	/workdir/go/src/cmd/compile/internal/gc/compile.go:163 +0x1f2 fp=0xc000491a90 sp=0xc000491a18 pc=0x10aaa52
cmd/compile/internal/gc.Main(0x11dd308)
	/workdir/go/src/cmd/compile/internal/gc/main.go:301 +0x178c fp=0xc000491ed8 sp=0xc000491a90 pc=0x10ad1cc
main.main()
	/workdir/go/src/cmd/compile/main.go:57 +0x171 fp=0xc000491f80 sp=0xc000491ed8 pc=0x10e5911
runtime.main()
	/workdir/go/src/runtime/proc.go:250 +0x1d3 fp=0xc000491fe0 sp=0xc000491f80 pc=0x43f4d3
runtime.goexit()
	/workdir/go/src/runtime/asm_amd64.s:1594 +0x1 fp=0xc000491fe8 sp=0xc000491fe0 pc=0x472061

(attn @golang/compiler)

[bcmills]

Needs a broader regexp:
greplogs -l -e 'goroutine \d+ \[running\]:\n(?:panic|runtime\.throw)(?:.+\n\t.+\n)*cmd/compile/internal/ssa\.Compile' --since=2022-01-01
2022-08-22T15:01:45-fc34fdb/linux-amd64-noopt
2022-08-19T19:39:48-9a1d3b0/linux-amd64-noopt

Looks like a possible Go 1.20 regression.

[mdempsky]

I think the problem is the compiler itself has been miscompiled, or the runtime version its using is buggy.

The first one (involving math/rand) is in debugging code that's only enabled by -d=ssa/check/on or similar, and it failed in a test case that doesn't use that flag.

The second one appears to be sigpanicking on a time.Now() call.

[aclements]

Possibly the same as #54779?

[cherrymui]

test/run.go adds -d=ssa/check/on for errorcheck tests https://cs.opensource.google/go/go/+/master:test/run.go;l=682
So at least the checkEnabled boolean condition is correct. It is still weird that it panics in math/rand though...

[bcmills]

greplogs -l -e 'goroutine \d+ \[running\]:\n(?:panic|runtime\.throw)(?:.+\n\t.+\n)*cmd/compile/internal/ssa\.Compile' --since=2022-08-23
2022-09-08T21:16:39-a9a3982/linux-amd64-noopt
2022-09-08T10:48:29-2960431/linux-amd64-noopt
2022-09-07T06:18:03-e2d8ed2/linux-amd64-noopt

[bcmills]

While we investigate this, is there something we can do to stabilize this build configuration? (Perhaps a change that can be reverted, or an optimization that can be disabled or re-enabled for the noopt flags?)

[cherrymui]

I haven't been able to identify a commit or the reason that causes the issue. The failure rate is quite low. Still looking.

[gopherbot]

Change https://go.dev/cl/431919 mentions this issue: runtime: make mSpanStateBox accessors nosplit