Confusing -O1 in build profile

[sjakobi]

$ cabal build
Resolving dependencies...
Build profile: -w ghc-8.8.1 -O1
In order, the following will be built (use -v for more details):
 - bsb-http-chunked-0.0.0.4 (lib) (first run)

What does the -O1 in the Build profile: line mean? The ghc-options for my library component include -O2, and the verbose log shows that ghc is invoked with -O2 too.

[23Skidoo]

It means that the local packages in the project are configured with -O1. However, as you correctly notice, this can be overridden on per-component basis in ghc-options.

[sjakobi]

Ah, thanks! In my case there weren't any other local packages that could be configured with -O1.

I first noticed it while benchmarking where it caused me much doubt about the validity of the numbers I was seeing.

What's the motivation for outputting this default(?) setting, especially when it doesn't apply / is overridden?

[phadej]

The motivation is that we consider `ghc-options: -O2` (any -O flag) to be at the very least questionable practice. In `cabal.project` you can have optimization: 2 for all local, or per package (also non-local) The core idea is that optimizations could be configured for all packages in an uniform way, without investigating if there’s some `dev`, `devel` or `fast` flag. Also as a bonus, changing optimization level (also possible from command line), won’t cause full recompilation (or worse: mixed-level compilation) as build products are kept separate.

…

On 1 Sep 2019, at 7.58, Simon Jakobi ***@***.***> wrote: Ah, thanks! In my case there weren't any other local packages that could be configured with -O1. I first noticed it while benchmarking where it caused me much doubt about the validity of the numbers I was seeing. What's the motivation for outputting this default(?) setting, especially when it doesn't apply / is overridden? — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub, or mute the thread.

[sjakobi]

The motivation is that we consider ghc-options: -O2 (any -O flag) to be at the very least questionable practice.

Interesting! Was there some kind of discussion that I could read?

Configuring the optimization level like this seems useful. Reporting -O1, when the actual optimization level applied is different, still seems confusing to me. Maybe cabal should also report the overrides then…

[jberryman]

I guess I'm not following the back and forth here.

It means that the local packages in the project are configured with -O1.

I have a project where I have a cabal.project.local that looks like:

package our-project
  optimization: 0
  documentation: false

and a .cabal file like:

name:                our-project
library
   ...
executable our-project
  ...

• When I do a new-build I see Build profile: -w ghc-8.6.5 -O1
• If I move optimization: 0 to the top-level I see ``Build profile: -w ghc-8.6.5 -O0`
• In both cases it looks like the library and executable in my project are built without optimizations (as intended)

So I'm not sure what "Build profile" is supposed to mean, and not sure if what it's reporting is correct, and not sure if I'm using my cabal.project.local file correctly

Related to #5353

[phadej]

The problem is the same unresolved one as with profiling. Prof and non-prof libraries can depend on each others, opt and non-opt libraries can depend on each other. The prof discussion needs input from @dcoutts as iirc he had some ideas.

…

On 22. Jan 2020, at 2.34, Brandon Simmons ***@***.***> wrote:  I guess I'm not following the back and forth here. It means that the local packages in the project are configured with -O1. I have a project where I have a cabal.project.local that looks like: package our-project optimization: 0 documentation: false and a .cabal file like: name: our-project library ... executable our-project ... When I do a new-build I see Build profile: -w ghc-8.6.5 -O1 If I move optimization: 0 to the top-level I see ``Build profile: -w ghc-8.6.5 -O0` In both cases it looks like the library and executable in my project are built without optimizations (as intended) So I'm not sure what "Build profile" is supposed to mean, and not sure if what it's reporting is correct, and not sure if I'm using my cabal.project.local file correctly Related to #5353 — You are receiving this because you commented. Reply to this email directly, view it on GitHub, or unsubscribe.

[tomjaguarpaw]

What does the -O1 in the Build profile: line mean? The ghc-options for my library component include -O2, and the verbose log shows that ghc is invoked with -O2 too.

FYI I have also just experienced puzzlement at this.

[fgaz]

I think it's the "global" optimization level, ie. the top-level optimization: in cabal.project.

[jneira]

and what about include that useful info in the message, something like Top level build profile...

[fgaz]

@sjakobi @jberryman @tomjaguarpaw is @jneira's proposal enough to clarify the meaning of that message? If not, any suggestions?

[tomjaguarpaw]

Well, it would certainly be better (and give something more substantial to Duck Duck Go for when confused).