cmd/compile: GOSSAHASH debugging switch needs to be accessible outside SSA

[dr2chase]

From time to time when debugging the compiler, it is helpful to use the GOSSAHASH environment variable to switch modified code on/off to search for exactly where a bug has its effect. However, this is currently limited to the ssa package. In the past I've edited the code to make it accessible outside of ssa when I needed it, and then discarded the edit. This seems like a waste of time, I've done this more than once, so it should be refactored into base.

[gopherbot]

Change https://go.dev/cl/418015 mentions this issue: cmd/compile: refactor GOSSAHASH debugging to make it usable outside ssa package.

[laboger]

Is there any documentation on how GOSSAHASH can be used? I see GOSSAFUNC mentioned in cmd/compile/internal/ssa/README.md.

[dr2chase]

Common case for me is to use it in conjunction with a program I wrote that uses it to implement a search (github.com/dr2chase/gossahash which could itself use better documentation). I added a comment to the new source code that might work for you, if it needs more, this is a good time to ask:

https://go-review.googlesource.com/c/go/+/418015/2/src/cmd/compile/internal/base/hashdebug.go

Oh, right away (checking my shell history for examples) I see a missing tweak GOMAXPROCS=1 gossahash -- ./make.bash, got to run the compiler single threaded if that is what is failing, if you want a good search.