2c9689ab0e
CL 653856 enabled stack allocation of variable-sized makeslice results. This CL adds debug hashing of that change, plus a debug flag to control the byte threshold used. The debug hashing machinery means we also now have a way to disable just the CL 653856 optimization by doing -gcflags='all=-d=variablemakehash=n' or similar, though the stderr output will then typically have many lines of debug hash output. Using this CL plus the bisect command, I was able to retroactively find one of the lines of code responsible for #73199: $ bisect -compile=variablemake go test -skip TestListWireGuardDrivers [...] bisect: FOUND failing change set --- change set #1 (enabling changes causes failure) ./security_windows.go:1321:38 (variablemake) ./security_windows.go:1321:38 (variablemake) --- Previously, I had tracked down those lines by diffing '-gcflags=-m=1' output and brief code inspection, but seeing the bisect was very nice. This CL also adds a compiler debug flag to control the threshold for stack allocation of variably sized make results. This can help us identify more code that is relying on certain stack allocations. This might be a temporary flag that we delete prior to Go 1.25 (given we would not want people to rely on it), or maybe it might make sense to keep it for some period of time beyond the release of Go 1.25 to help the ecosystem shake out other bugs. Using these two flags together (and picking a threshold of 64 rather than the default of 32), it looks for example like this x/sys/windows code might be relying on stack allocation of a byte slice: $ bisect -compile=variablemake go test -gcflags=-d=variablemakethreshold=64 -skip TestListWireGuardDrivers [...] bisect: FOUND failing change set --- change set #1 (enabling changes causes failure) ./syscall_windows_test.go:1178:16 (variablemake) Updates #73199 Fixes #73253 Change-Id: I160179a0e3c148c3ea86be5c9b6cea8a52c3e5b7 Reviewed-on: https://go-review.googlesource.com/c/go/+/663795 Auto-Submit: Keith Randall <khr@golang.org> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com> Reviewed-by: Keith Randall <khr@golang.org> Reviewed-by: Keith Randall <khr@google.com> LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
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