ghc -ddump-simpl-stats output missing

[harendra-kumar]

I used the following command line to print the ghc simplifier stats:

stack build --ghc-options -ddump-simpl-stats

I also tried the -v option but I could not find the output of the command anywhere. Neither on console nor in the logs. Though when I invoked ghc directly I see the output as follows. I expect to find the same with stack build as well.

cueball:/vol/hosts/cueball/workspace/projects/unicode-transforms/Data/Text$ stack ghc --package unicode-transforms -- -ddump-simpl-stats NormalizeNative.hs
[1 of 1] Compiling Data.Text.NormalizeNative ( NormalizeNative.hs, NormalizeNative.o )

==================== Grand total simplifier statistics ====================
Total ticks:     2

1 PreInlineUnconditionally 1 t_a2Uk
1 BetaReduction 1 t_a2Uk
2 SimplifierDone 2

[mgsloan]

This is likely due to stack providing the ghc options -ddump-hi -ddump-to-file so that it can get build dependency info. Not sure what to about that, except perhaps putting the file to the console or something (but without the ddump-hi portions)

[harendra-kumar]

Even a pointer to the dump file location at the end of the compilation should help. At least the user will know what happened and where the info can be found.

[mgsloan]

Yeah, that's a good solution!

[harendra-kumar]

There is another strange problem when using -ddump compiler options in the cabal file, the dump output for stg/cmm/asm is duplicated in the dump file. This is the case for stg/cmm/asm outputs but strangely not for the core output.

[mgsloan]

It's strange to me that the ddump output appends, that may be an oversight in ghc, because for the dump-hi files it recreates them.

It'd be tricky to correctly clear out the dump files. We can either:

1. Remove all dump files. This means that for partial recompiles, we'd only have dump files for stuff that recompiled. So to get all ddump data you'd need to do -fforce-recomp.

2. Somehow know which modules will recompile, and delete the associated dump files.

[harendra-kumar]

Earlier I thought it appends. But it does not append it just appears twice in each file every time. Strangely it does not happen for .dump-simpl but happens for all other dump files. Perhaps some ghc option is causing it, not sure which one.

[sjakobi]

Even a pointer to the dump file location at the end of the compilation should help.

This idea is also being tracked in #1727.

[snoyberg]

Closing in favor of #1727. Also, this should be addressed more completely by #4545