build: significant build cache size increase on tip

[cherrymui]

$ mkdir /tmp/cache1.24
$ git checkout go1.24.0
$ GOCACHE=/tmp/cache1.24 ./make.bash
...
$ mkdir /tmp/cachetip
$ git checkout master && git pull
$ GOCACHE=/tmp/cachetip ./make.bash
...
$ du -sh /tmp/cache*
 39M	/tmp/cache1.24
663M	/tmp/cachetip

(This is on darwin/arm64. Other platforms might be similar.)

This is concerning.

[prattmic]

I planned to start a bisect, but even 9da530f has a big cache, even though it should be very similar to 1.24.

[cherrymui]

Interesting. Apparently if I create a dummy VERSION file at tip, the cache size backs to 39M.

I'll see what the cache size is before without a VERSION file.

[prattmic]

FWIW, if I do GOCACHE=<tmp location> go build cmd/compile at go1.24.0 and 9da530f, both have identical cache size (169MB). Not sure why that is bigger than make.bash for 1.24...

[cherrymui]

With Go 1.23.0, if I remove the VERSION file, I got 599M. Smaller than tip, but not too much.

cmd/dist does different things depending on whether we have a VERSION file https://cs.opensource.google/go/go/+/master:src/cmd/dist/build.go;l=1586 .
If we have one (e.g. for a Go release), it uses GOROOT/pkg/obj, which then get deleted at the end. If not, it uses the actual GOCACHE.

So I guess actually there is no big increase. Maybe there is some builder issues...