cmd/compile: out of memory compiling cmd/compile/internal/ssa with 1GB RAM #27739
Description
Building tip on Ubuntu 18.04 on a Digital Ocean VM with one 1GB of RAM at commit 83dfc3b
phil@spare0:~/go/src$ uname -a
Linux spare0 4.15.0-30-generic #32-Ubuntu SMP Thu Jul 26 17:42:43 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
I can reproduce this out-of-memory condition 100% of the time (in the prove pass in SSA):
Building Go cmd/dist using /home/phil/go-bootstrap.
Building Go toolchain1 using /home/phil/go-bootstrap.
Building Go bootstrap cmd/go (go_bootstrap) using Go toolchain1.
Building Go toolchain2 using go_bootstrap and Go toolchain1.
# cmd/compile/internal/ssa
fatal error: runtime: out of memory
runtime stack:
runtime.throw(0x9f727f, 0x16)
/home/phil/go/src/runtime/panic.go:608 +0x72
runtime.sysMap(0xc02c000000, 0x4000000, 0xe7d258)
/home/phil/go/src/runtime/mem_linux.go:156 +0xc7
runtime.(*mheap).sysAlloc(0xe5a580, 0x4000000, 0xe5a598, 0x7f0d87065308)
/home/phil/go/src/runtime/malloc.go:619 +0x1c7
runtime.(*mheap).grow(0xe5a580, 0x3, 0x0)
/home/phil/go/src/runtime/mheap.go:920 +0x42
runtime.(*mheap).allocSpanLocked(0xe5a580, 0x3, 0xe7d268, 0x400)
/home/phil/go/src/runtime/mheap.go:848 +0x337
runtime.(*mheap).alloc_m(0xe5a580, 0x3, 0x50, 0x7f0d87351fff)
/home/phil/go/src/runtime/mheap.go:692 +0x119
runtime.(*mheap).alloc.func1()
/home/phil/go/src/runtime/mheap.go:759 +0x4c
runtime.(*mheap).alloc(0xe5a580, 0x3, 0x7f0d87010050, 0x7f0d87065270)
/home/phil/go/src/runtime/mheap.go:758 +0x8a
runtime.(*mcentral).grow(0xe5ccb8, 0x0)
/home/phil/go/src/runtime/mcentral.go:232 +0x94
runtime.(*mcentral).cacheSpan(0xe5ccb8, 0x1fe)
/home/phil/go/src/runtime/mcentral.go:106 +0x2f8
runtime.(*mcache).refill(0x7f0d8b82a000, 0xc000020050)
/home/phil/go/src/runtime/mcache.go:122 +0x95
runtime.(*mcache).nextFree.func1()
/home/phil/go/src/runtime/malloc.go:749 +0x32
runtime.systemstack(0x455ad9)
/home/phil/go/src/runtime/asm_amd64.s:351 +0x66
runtime.mstart()
/home/phil/go/src/runtime/proc.go:1229
1GB of memory has been more than enough to build the toolchain in the past.
Barring any clever ideas about how to debug this, I'll try to bisect and hope that there was only one commit that reliably introduced this regression.