cmd/compile: compiler crash

[bradfitz]

Seen on a trybot run:

https://storage.googleapis.com/go-build-log/571e0937/freebsd-amd64-gce101_a4100224.log

freebsd-amd64-gce101 at 571e09379c5243f5dd1b6a69eeb42ffe5c20651d
....

##### Testing race detector
# crypto/elliptic
dst [0xc42003db00]
.   LITERAL-0 l(1248) tc(1) assigned int
.   .   LITERAL-0 l(1248) tc(1) int
crypto/elliptic/p224.go:88: cannot assign to int(0)
crypto/elliptic/p256_amd64.go:96: internal compiler error: escassign: unexpected dst

goroutine 1 [running]:
runtime/debug.Stack(0x0, 0x0, 0x0)
    /tmp/workdir/go/src/runtime/debug/stack.go:24 +0x6f
cmd/compile/internal/gc.Fatalf(0x8cc2b7, 0x19, 0x0, 0x0, 0x0)
    /tmp/workdir/go/src/cmd/compile/internal/gc/subr.go:165 +0x236
cmd/compile/internal/gc.escassign(0xc4205297a0, 0xc42003db00, 0xc42003db00, 0x0)
    /tmp/workdir/go/src/cmd/compile/internal/gc/esc.go:1015 +0xbd7
cmd/compile/internal/gc.escassignNilWhy(0xc4205297a0, 0xc42003db00, 0xc42003db00, 0x8c3b70, 0xb)
    /tmp/workdir/go/src/cmd/compile/internal/gc/esc.go:976 +0x63
cmd/compile/internal/gc.esc(0xc4205297a0, 0xc4207b67e0, 0xc4207b6750)
    /tmp/workdir/go/src/cmd/compile/internal/gc/esc.go:758 +0xeca
cmd/compile/internal/gc.esclist(0xc4205297a0, 0xc4207b0100, 0xc4207b6750)
    /tmp/workdir/go/src/cmd/compile/internal/gc/esc.go:602 +0x5a
cmd/compile/internal/gc.esc(0xc4205297a0, 0xc4207b6750, 0xc4207b6510)
    /tmp/workdir/go/src/cmd/compile/internal/gc/esc.go:620 +0xa7
cmd/compile/internal/gc.esclist(0xc4205297a0, 0xc4207b0120, 0xc4207b6510)
    /tmp/workdir/go/src/cmd/compile/internal/gc/esc.go:602 +0x5a
cmd/compile/internal/gc.esc(0xc4205297a0, 0xc4207b6510, 0xc4207b6cf0)
    /tmp/workdir/go/src/cmd/compile/internal/gc/esc.go:655 +0x245
cmd/compile/internal/gc.esclist(0xc4205297a0, 0xc4207b0640, 0xc4207b6cf0)
    /tmp/workdir/go/src/cmd/compile/internal/gc/esc.go:602 +0x5a
cmd/compile/internal/gc.esc(0xc4205297a0, 0xc4207b6cf0, 0xc4205d6e10)
    /tmp/workdir/go/src/cmd/compile/internal/gc/esc.go:620 +0xa7
cmd/compile/internal/gc.esc(0xc4205297a0, 0xc4205d6e10, 0xc4205d70e0)
    /tmp/workdir/go/src/cmd/compile/internal/gc/esc.go:653 +0x1f7
cmd/compile/internal/gc.esc(0xc4205297a0, 0xc4205d70e0, 0xc4205d7170)
    /tmp/workdir/go/src/cmd/compile/internal/gc/esc.go:653 +0x1f7
cmd/compile/internal/gc.esc(0xc4205297a0, 0xc4205d7170, 0xc4205d2990)
    /tmp/workdir/go/src/cmd/compile/internal/gc/esc.go:653 +0x1f7
cmd/compile/internal/gc.esclist(0xc4205297a0, 0xc4205bd6a0, 0xc4205d2990)
    /tmp/workdir/go/src/cmd/compile/internal/gc/esc.go:602 +0x5a
cmd/compile/internal/gc.escfunc(0xc4205297a0, 0xc4205d2990)
    /tmp/workdir/go/src/cmd/compile/internal/gc/esc.go:544 +0x1a7
cmd/compile/internal/gc.escAnalyze(0xc420564a80, 0x1, 0x4, 0xc420721b00)
    /tmp/workdir/go/src/cmd/compile/internal/gc/esc.go:467 +0x47c
cmd/compile/internal/gc.(*bottomUpVisitor).visit(0xc420721ba8, 0xc4205d2990, 0xc400000034)
    /tmp/workdir/go/src/cmd/compile/internal/gc/esc.go:106 +0x29e
cmd/compile/internal/gc.visitBottomUp(0xc4200e1c00, 0x5f, 0x80, 0x916ae8)
    /tmp/workdir/go/src/cmd/compile/internal/gc/esc.go:62 +0xb7
cmd/compile/internal/gc.escapes(0xc4200e1c00, 0x5f, 0x80)
    /tmp/workdir/go/src/cmd/compile/internal/gc/esc.go:186 +0x41
cmd/compile/internal/gc.Main()
    /tmp/workdir/go/src/cmd/compile/internal/gc/main.go:447 +0x18e6
cmd/compile/internal/amd64.Main()
    /tmp/workdir/go/src/cmd/compile/internal/amd64/galign.go:96 +0x381
main.main()
    /tmp/workdir/go/src/cmd/compile/main.go:33 +0x286

2016/05/20 20:49:43 Failed: exit status 2

/cc @randall77 @dr2chase @mdempsky

[bradfitz]

Also a non-trybot compiler crash:

https://build.golang.org/log/9fc746798fd4e909296ec1000d07598e240cc80a

darwin-386-10_10 at 85e39f838722a1521e09288cddfe378843d662fb
...
ok      log/syslog  2.121s
# math/big
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x15adf5]

goroutine 1 [running]:
panic(0x4cdfa0, 0x10998008)
    /private/var/folders/5h/sqs3zkxd12zclcslj67vccqh0000gp/T/workdir/go/src/runtime/panic.go:500 +0x325
cmd/compile/internal/gc.nodedump(0x11802200, 0x0, 0x0, 0x0)
    /private/var/folders/5h/sqs3zkxd12zclcslj67vccqh0000gp/T/workdir/go/src/cmd/compile/internal/gc/fmt.go:1525 +0x1795
cmd/compile/internal/gc.Nconv(0x11802200, 0x0, 0x0, 0x0)
    /private/var/folders/5h/sqs3zkxd12zclcslj67vccqh0000gp/T/workdir/go/src/cmd/compile/internal/gc/fmt.go:1771 +0x10d
cmd/compile/internal/gc.Dump(0x4fb9dd, 0x9, 0x11802200)
    /private/var/folders/5h/sqs3zkxd12zclcslj67vccqh0000gp/T/workdir/go/src/cmd/compile/internal/gc/fmt.go:1823 +0x3b
cmd/compile/internal/gc.typecheck1(0x11802200, 0x1, 0x0)
    /private/var/folders/5h/sqs3zkxd12zclcslj67vccqh0000gp/T/workdir/go/src/cmd/compile/internal/gc/typecheck.go:279 +0xb93
cmd/compile/internal/gc.typecheck(0x11802200, 0x1, 0x0)
    /private/var/folders/5h/sqs3zkxd12zclcslj67vccqh0000gp/T/workdir/go/src/cmd/compile/internal/gc/typecheck.go:188 +0x5ff
cmd/compile/internal/gc.typecheckslice(0x110c0000, 0x1, 0x1, 0x1)
    /private/var/folders/5h/sqs3zkxd12zclcslj67vccqh0000gp/T/workdir/go/src/cmd/compile/internal/gc/typecheck.go:49 +0x53
cmd/compile/internal/gc.typecheck1(0x12f324e0, 0x1, 0x12f32480)
    /private/var/folders/5h/sqs3zkxd12zclcslj67vccqh0000gp/T/workdir/go/src/cmd/compile/internal/gc/typecheck.go:2021 +0xee33
cmd/compile/internal/gc.typecheck(0x12f324e0, 0x1, 0x12f32480)
    /private/var/folders/5h/sqs3zkxd12zclcslj67vccqh0000gp/T/workdir/go/src/cmd/compile/internal/gc/typecheck.go:188 +0x5ff
cmd/compile/internal/gc.typecheckslice(0x12f20220, 0x6, 0x8, 0x1)
    /private/var/folders/5h/sqs3zkxd12zclcslj67vccqh0000gp/T/workdir/go/src/cmd/compile/internal/gc/typecheck.go:49 +0x53
cmd/compile/internal/gc.copyany(0x10fb5e60, 0x12f3b80c, 0x10fb5c00, 0x12f32120)
    /private/var/folders/5h/sqs3zkxd12zclcslj67vccqh0000gp/T/workdir/go/src/cmd/compile/internal/gc/walk.go:3031 +0xaf8
cmd/compile/internal/gc.walkexpr(0x10fb5e60, 0x12f3b80c, 0x0)
    /private/var/folders/5h/sqs3zkxd12zclcslj67vccqh0000gp/T/workdir/go/src/cmd/compile/internal/gc/walk.go:1361 +0x96cf
cmd/compile/internal/gc.walkstmt(0x10fb5e60, 0x10fb5ce0)
    /private/var/folders/5h/sqs3zkxd12zclcslj67vccqh0000gp/T/workdir/go/src/cmd/compile/internal/gc/walk.go:193 +0x28a
cmd/compile/internal/gc.walkstmtlist(0x12c49c00, 0x65, 0x80)
    /private/var/folders/5h/sqs3zkxd12zclcslj67vccqh0000gp/T/workdir/go/src/cmd/compile/internal/gc/walk.go:81 +0x4b
cmd/compile/internal/gc.walk(0x10fb1f80)
    /private/var/folders/5h/sqs3zkxd12zclcslj67vccqh0000gp/T/workdir/go/src/cmd/compile/internal/gc/walk.go:66 +0x38b
cmd/compile/internal/gc.compile(0x10fb1f80)
    /private/var/folders/5h/sqs3zkxd12zclcslj67vccqh0000gp/T/workdir/go/src/cmd/compile/internal/gc/pgen.go:391 +0x79d
cmd/compile/internal/gc.funccompile(0x10fb1f80)
    /private/var/folders/5h/sqs3zkxd12zclcslj67vccqh0000gp/T/workdir/go/src/cmd/compile/internal/gc/dcl.go:1278 +0x161
cmd/compile/internal/gc.Main()
    /private/var/folders/5h/sqs3zkxd12zclcslj67vccqh0000gp/T/workdir/go/src/cmd/compile/internal/gc/main.go:465 +0x1b98
cmd/compile/internal/x86.Main()
    /private/var/folders/5h/sqs3zkxd12zclcslj67vccqh0000gp/T/workdir/go/src/cmd/compile/internal/x86/galign.go:80 +0x2d6
main.main()
    /private/var/folders/5h/sqs3zkxd12zclcslj67vccqh0000gp/T/workdir/go/src/cmd/compile/main.go:31 +0x111
ok      math    0.006s
FAIL    math/big [build failed]

[mdempsky]

The stack traces are distinct enough that they seem like separate issues, but it seems surprising that we'd suddenly introduce two crasher bugs into the compiler.

[bradfitz]

Paging Dr. @aclements.

Maybe related: bogus race reports in #15739?

[mdempsky]

The second stack trace doesn't look related to race detection.

I'm running those two compiles (math/big for freebsd/amd64, and crypto/elliptic for darwin/386) in a loop on my linux/amd64 workstation, but no repros yet.

Edit: 60k crypto/elliptic and 20k math/big compiles later and still no repros.

[aclements]

I agree that these looks like completely unrelated bugs. The first one is an internal compiler check failing during escape analysis and the other is an outright crash during type checking.

The first one (escassign: unexpected dst) has never appeared on the dashboard.

The second one's a little hard to say, but it looks like it's never appeared except for the one time linked in the original post.

[dr2chase]

Perhaps a change in something that was inlined? In

dst [0xc42003db00]
.   LITERAL-0 l(1248) tc(1) assigned int
.   .   LITERAL-0 l(1248) tc(1) int
crypto/elliptic/p224.go:88: cannot assign to int(0)
crypto/elliptic/p256_amd64.go:96: internal compiler error: escassign: unexpected dst

both errors (in separate files) are complaining about the same root cause, the equivalent of

0 = something

That scrap of tree in the error message is the unexpected dst from escape analysis.

[mdempsky]

544k math/big and 1.57M crypto/elliptic compiles later, I've had three cmd/compile failures compiling math/big. (Edit: These compiles are at revision 85e39f8.)

First:

dst [0xb3b4f1]
.   XXX x(0+0)
./int.go:533: internal compiler error: escassign: unexpected dst

goroutine 1 [running]:
runtime/debug.Stack(0x0, 0x0, 0x0)
    /usr/local/google/home/mdempsky/wd/go/src/runtime/debug/stack.go:24 +0x6f
cmd/compile/internal/gc.Fatalf(0x8ce17c, 0x19, 0x0, 0x0, 0x0)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/subr.go:165 +0x236
cmd/compile/internal/gc.escassign(0xc420599440, 0xb3b4f1, 0xc420bf8e10, 0x0)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:1015 +0xbd7
cmd/compile/internal/gc.escassignNilWhy(0xc420599440, 0xb3b4f1, 0xc420bf8e10, 0x8c5954, 0xb)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:976 +0x63
cmd/compile/internal/gc.esc(0xc420599440, 0xc420bf9ef0, 0xc4203ecf30)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:758 +0xec7
cmd/compile/internal/gc.esclist(0xc420599440, 0xc420404740, 0xc4203ecf30)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:602 +0x5a
cmd/compile/internal/gc.esc(0xc420599440, 0xc4203ecf30, 0xc420bf9a70)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:620 +0xa7
cmd/compile/internal/gc.esclist(0xc420599440, 0xc420431780, 0xc420bf9a70)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:602 +0x5a
cmd/compile/internal/gc.esc(0xc420599440, 0xc420bf9a70, 0xc4207fa3f0)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:656 +0x26f
cmd/compile/internal/gc.esclist(0xc420599440, 0xc4207e7120, 0xc4207fa3f0)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:602 +0x5a
cmd/compile/internal/gc.esc(0xc420599440, 0xc4207fa3f0, 0xc4207f5200)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:655 +0x248
cmd/compile/internal/gc.esclist(0xc420599440, 0xc4207e73c0, 0xc4207f5200)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:602 +0x5a
cmd/compile/internal/gc.escfunc(0xc420599440, 0xc4207f5200)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:544 +0x1a7
cmd/compile/internal/gc.escAnalyze(0xc420970a10, 0x1, 0xe, 0xc420a75600)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:467 +0x47c
cmd/compile/internal/gc.(*bottomUpVisitor).visit(0xc420a75ba8, 0xc4207f5200, 0xfc)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:106 +0x29e
cmd/compile/internal/gc.(*bottomUpVisitor).visitcode(0xc420a75ba8, 0xc4209ef680, 0xfc, 0xc4000000fc)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:137 +0x164
cmd/compile/internal/gc.(*bottomUpVisitor).visitcode(0xc420a75ba8, 0xc4209ef710, 0xfc, 0xc420a75ba8)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:126 +0x8b
cmd/compile/internal/gc.(*bottomUpVisitor).visitcodelist(0xc420a75ba8, 0xc4209d7060, 0xc4000000fc, 0xfc)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:114 +0x5c
cmd/compile/internal/gc.(*bottomUpVisitor).visitcode(0xc420a75ba8, 0xc4209efb00, 0xfc, 0xfc)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:124 +0x44
cmd/compile/internal/gc.(*bottomUpVisitor).visitcodelist(0xc420a75ba8, 0xc4209d7240, 0xfc, 0xfc)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:114 +0x5c
cmd/compile/internal/gc.(*bottomUpVisitor).visitcode(0xc420a75ba8, 0xc4209ee990, 0xfc, 0xd9b8396e000000fc)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:128 +0xd3
cmd/compile/internal/gc.(*bottomUpVisitor).visitcodelist(0xc420a75ba8, 0xc4209d7260, 0xfc, 0xc4000000fc)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:114 +0x5c
cmd/compile/internal/gc.(*bottomUpVisitor).visitcode(0xc420a75ba8, 0xc4209ed170, 0xfc, 0x40a2c3)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:127 +0xaf
cmd/compile/internal/gc.(*bottomUpVisitor).visitcodelist(0xc420a75ba8, 0xc4209d72a0, 0xc4000000fc, 0xc420a75894)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:114 +0x5c
cmd/compile/internal/gc.(*bottomUpVisitor).visit(0xc420a75ba8, 0xc4209ece10, 0xfa)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:80 +0x12c
cmd/compile/internal/gc.(*bottomUpVisitor).visitcode(0xc420a75ba8, 0xc4205e8120, 0xfa, 0xfa)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:137 +0x164
cmd/compile/internal/gc.(*bottomUpVisitor).visitcodelist(0xc420a75ba8, 0xc4205de760, 0xfa, 0xc4000000fa)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:114 +0x5c
cmd/compile/internal/gc.(*bottomUpVisitor).visitcode(0xc420a75ba8, 0xc4205e70e0, 0xfa, 0xc4000000fa)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:128 +0xd3
cmd/compile/internal/gc.(*bottomUpVisitor).visitcodelist(0xc420a75ba8, 0xc4205de7a0, 0xfa, 0xc4000000fa)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:114 +0x5c
cmd/compile/internal/gc.(*bottomUpVisitor).visitcode(0xc420a75ba8, 0xc4205e5830, 0xfa, 0xc4000000fa)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:127 +0xaf
cmd/compile/internal/gc.(*bottomUpVisitor).visitcodelist(0xc420a75ba8, 0xc4205de800, 0xfa, 0xc4000000fa)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:114 +0x5c
cmd/compile/internal/gc.(*bottomUpVisitor).visitcode(0xc420a75ba8, 0xc4205e4fc0, 0xfa, 0xc420a75ba8)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:128 +0xd3
cmd/compile/internal/gc.(*bottomUpVisitor).visitcodelist(0xc420a75ba8, 0xc4205de960, 0xc4000000fa, 0xc4000000fa)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:114 +0x5c
cmd/compile/internal/gc.(*bottomUpVisitor).visitcode(0xc420a75ba8, 0xc4205e4f30, 0xfa, 0xfa)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:127 +0xaf
cmd/compile/internal/gc.(*bottomUpVisitor).visitcodelist(0xc420a75ba8, 0xc4205de9c0, 0xc4000000fa, 0xc420a75b34)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:114 +0x5c
cmd/compile/internal/gc.(*bottomUpVisitor).visit(0xc420a75ba8, 0xc4205e42d0, 0xc4000000f6)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:80 +0x12c
cmd/compile/internal/gc.visitBottomUp(0xc420871000, 0x147, 0x200, 0x918dc0)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:62 +0xb7
cmd/compile/internal/gc.escapes(0xc420871000, 0x147, 0x200)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/esc.go:186 +0x41
cmd/compile/internal/gc.Main()
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/main.go:447 +0x18f3
cmd/compile/internal/amd64.Main()
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/amd64/galign.go:96 +0x381
main.main()
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/main.go:33 +0x286

Second:

./nat.go:82: internal compiler error: orderstmt NAME

goroutine 1 [running]:
runtime/debug.Stack(0x0, 0x0, 0x0)
    /usr/local/google/home/mdempsky/wd/go/src/runtime/debug/stack.go:24 +0x6f
cmd/compile/internal/gc.Fatalf(0x8c66ed, 0xc, 0xc420a7ca70, 0x1, 0x1)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/subr.go:165 +0x236
cmd/compile/internal/gc.orderstmt(0xc420b9a510, 0xc420a7cf18)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:481 +0x2c45
cmd/compile/internal/gc.orderstmtlist(0xc420b920c0, 0xc420a7cf18)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:245 +0x50
cmd/compile/internal/gc.orderinit(0xc420b9aa20, 0xc420a7cf18)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:298 +0x2f
cmd/compile/internal/gc.orderstmt(0xc420b9aa20, 0xc420a7cf18)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:477 +0x76
cmd/compile/internal/gc.orderstmtlist(0xc42049c040, 0xc420a7cf18)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:245 +0x50
cmd/compile/internal/gc.orderblockNodes(0xc420b9a888)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:264 +0x49
cmd/compile/internal/gc.orderstmt(0xc420b9a870, 0xc420a7d868)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:694 +0xcfc
cmd/compile/internal/gc.orderstmtlist(0xc420b92220, 0xc420a7d868)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:245 +0x50
cmd/compile/internal/gc.orderinit(0xc420b9b050, 0xc420a7d868)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:298 +0x2f
cmd/compile/internal/gc.orderexpr(0xc420b9b050, 0xc420a7d868, 0xc420899290, 0xc420899290)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:992 +0x62
cmd/compile/internal/gc.orderstmt(0xc42089eab0, 0xc420a7d868)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:489 +0x33f7
cmd/compile/internal/gc.orderstmtlist(0xc42087dde0, 0xc420a7d868)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:245 +0x50
cmd/compile/internal/gc.orderblockNodes(0xc420899698)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:264 +0x49
cmd/compile/internal/gc.order(0xc420899680)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:56 +0xd6
cmd/compile/internal/gc.compile(0xc420899680)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/pgen.go:385 +0x19d
cmd/compile/internal/gc.funccompile(0xc420899680)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/dcl.go:1278 +0x17d
cmd/compile/internal/gc.Main()
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/main.go:465 +0x19a9
cmd/compile/internal/amd64.Main()
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/amd64/galign.go:96 +0x381
main.main()
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/main.go:33 +0x286

Third:

./nat.go:82: internal compiler error: orderstmt NAME

goroutine 1 [running]:
runtime/debug.Stack(0x0, 0x0, 0x0)
    /usr/local/google/home/mdempsky/wd/go/src/runtime/debug/stack.go:24 +0x6f
cmd/compile/internal/gc.Fatalf(0x8c66ed, 0xc, 0xc421218a80, 0x1, 0x1)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/subr.go:165 +0x236
cmd/compile/internal/gc.orderstmt(0xc420ba06c0, 0xc421218f28)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:481 +0x2c45
cmd/compile/internal/gc.orderstmtlist(0xc420b980a0, 0xc421218f28)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:245 +0x50
cmd/compile/internal/gc.orderinit(0xc420ba0bd0, 0xc421218f28)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:298 +0x2f
cmd/compile/internal/gc.orderstmt(0xc420ba0bd0, 0xc421218f28)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:477 +0x76
cmd/compile/internal/gc.orderstmtlist(0xc42177c500, 0xc421218f28)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:245 +0x50
cmd/compile/internal/gc.orderblockNodes(0xc420ba0a38)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:264 +0x49
cmd/compile/internal/gc.orderstmt(0xc420ba0a20, 0xc421219878)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:694 +0xcfc
cmd/compile/internal/gc.orderstmtlist(0xc420b98200, 0xc421219878)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:245 +0x50
cmd/compile/internal/gc.orderinit(0xc420ba1200, 0xc421219878)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:298 +0x2f
cmd/compile/internal/gc.orderexpr(0xc420ba1200, 0xc421219878, 0xc4208a3440, 0xc4208a3440)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:992 +0x62
cmd/compile/internal/gc.orderstmt(0xc4208a8c60, 0xc421219878)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:489 +0x33f7
cmd/compile/internal/gc.orderstmtlist(0xc420887dc0, 0xc421219878)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:245 +0x50
cmd/compile/internal/gc.orderblockNodes(0xc4208a3848)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:264 +0x49
cmd/compile/internal/gc.order(0xc4208a3830)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/order.go:56 +0xd6
cmd/compile/internal/gc.compile(0xc4208a3830)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/pgen.go:385 +0x19d
cmd/compile/internal/gc.funccompile(0xc4208a3830)
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/dcl.go:1278 +0x17d
cmd/compile/internal/gc.Main()
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/gc/main.go:465 +0x19a9
cmd/compile/internal/amd64.Main()
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/internal/amd64/galign.go:96 +0x381
main.main()
    /usr/local/google/home/mdempsky/wd/go/src/cmd/compile/main.go:33 +0x286

[mdempsky]

Interestingly, those last two panics have identical stack traces (ignoring argument values).

[rsc]

When I was working on the liveness code I did find a function in the compiler that was being miscompiled by the same bug. It could be that (#15747).

[rsc]

To be clear, "miscompiled" means the liveness bitmaps were not quite right. That could manifest as flaky corruption like here. If the timing looks right, I'd say wait for my fix to land and see if this happens again.

[josharian]

@mdempsky want to kick off another round of millions of compiles to see whether this looks fixed by the other liveness fixes?

[mdempsky]

@josharian Running again at 3ba3155.

[aclements]

@mdempsky, any results from your run?

[mdempsky]

@aclements 250k compiles of math/big, but no crashes.