llvm dev - Jul 2015 - [LLVMdev] Any objections to turning on -Wunused-parameter? (and any other -Wunused-* that are off?)

LLVM and Clang both have lots of objects that are passed through many
different API boundaries. Things like AliasAnalysis in LLVM or Sema in
Clang get threaded all over the place.

Over times, refactoring can often cause the parameters (or local variables,
or member variables, etc) to become dead. If we notice this, we can often
un-thread the interface through our APIs, sometimes even reducing coupling,
etc.

But currently -Wunused-parameter is hard disabled. I've not checked to see
if there are any other disabling of -Wunused-* variants, but I'd like to
move the project toward firmly enabling them and being clean with them.

The technique I'd like to use is leaving out names of unused parameters,
using a /*CommentedName*/ if there is a useful name, otherwise just
omitting the name.

All of this will require a reasonable amount of cleanup across the projects
which I'm happy to do prior to flipping defaults around. Thoughts? Any
concerns or objections?

(I'll ask the same question and ofter to either enact the cleanups or
toggle the warning(s) back off for each of the less intertwined subprojects
like LLD, LLDB, Polly, etc.)

-Chandler
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On 18 July 2015 at 10:48, Chandler Carruth <chandlerc at gmail.com>
wrote:
> But currently -Wunused-parameter is hard disabled. I've not checked to
see
> if there are any other disabling of -Wunused-* variants, but I'd like
to
> move the project toward firmly enabling them and being clean with them.
+1

> The technique I'd like to use is leaving out names of unused
parameters,
> using a /*CommentedName*/ if there is a useful name, otherwise just
omitting
> the name.
I'd just get rid of everything. Often, outdated comments can be more
harmful than no comments.

cheers,
--renato

> On Jul 18, 2015, at 2:48 AM, Chandler Carruth <chandlerc at
gmail.com> wrote:
> 
> LLVM and Clang both have lots of objects that are passed through many
different API boundaries. Things like AliasAnalysis in LLVM or Sema in Clang get
threaded all over the place.
> 
> Over times, refactoring can often cause the parameters (or local variables,
or member variables, etc) to become dead. If we notice this, we can often
un-thread the interface through our APIs, sometimes even reducing coupling, etc.
> 
> But currently -Wunused-parameter is hard disabled. I've not checked to
see if there are any other disabling of -Wunused-* variants, but I'd like to
move the project toward firmly enabling them and being clean with them.
> 
> The technique I'd like to use is leaving out names of unused
parameters, using a /*CommentedName*/ if there is a useful name, otherwise just
omitting the name.
> 
> All of this will require a reasonable amount of cleanup across the projects
which I'm happy to do prior to flipping defaults around. Thoughts? Any
concerns or objections?
+1.  We should also consider other general goodness warnings as well.

-Chris

I'd be very happy to see this turned on as a warning; I'd be very 
reluctant to see it turned on as a error.  During a lot of code 
cleanups, the intermediate state of "deleted, but dead args still passed 
in" is a very useful intermediate step.  It greatly simplifies review to 
be able to separate the meat of the semantic change from the "just 
deleting a bunch of dead args" patch.  I'd be very very reluctant to 
create a situation where the patch with the semantic change but without 
the argument cleanup won't pass all the build bots.

Philip

(1 inline comment below as well)

On 07/18/2015 02:48 AM, Chandler Carruth wrote:
> LLVM and Clang both have lots of objects that are passed through many 
> different API boundaries. Things like AliasAnalysis in LLVM or Sema in 
> Clang get threaded all over the place.
>
> Over times, refactoring can often cause the parameters (or local 
> variables, or member variables, etc) to become dead. If we notice 
> this, we can often un-thread the interface through our APIs, sometimes 
> even reducing coupling, etc.
>
> But currently -Wunused-parameter is hard disabled. I've not checked to 
> see if there are any other disabling of -Wunused-* variants, but I'd 
> like to move the project toward firmly enabling them and being clean 
> with them.
>
> The technique I'd like to use is leaving out names of unused 
> parameters, using a /*CommentedName*/ if there is a useful name, 
> otherwise just omitting the name.
Sorry, could you rephrase?  Not sure what you're getting at
here.
>
> All of this will require a reasonable amount of cleanup across the 
> projects which I'm happy to do prior to flipping defaults around. 
> Thoughts? Any concerns or objections?
>
> (I'll ask the same question and ofter to either enact the cleanups or 
> toggle the warning(s) back off for each of the less intertwined 
> subprojects like LLD, LLDB, Polly, etc.)
>
> -Chandler
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
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On Mon, Jul 20, 2015 at 4:18 PM, Philip Reames <listmail at
philipreames.com>
wrote:
>  I'd be very happy to see this turned on as a warning; I'd be very
> reluctant to see it turned on as a error.  During a lot of code cleanups,
> the intermediate state of "deleted, but dead args still passed
in" is a
> very useful intermediate step.  It greatly simplifies review to be able to
> separate the meat of the semantic change from the "just deleting a
bunch of
> dead args" patch.  I'd be very very reluctant to create a
situation where
> the patch with the semantic change but without the argument cleanup
won't
> pass all the build bots.
>
Yep - I recall Chandler expressing similar consternation when he & I have
discussed -Wunreachable-code so I was a bit surprised to see the suggestion.

But that said, in this case it doesn't seem too costly to comment out the
name of the parameter in the first patch - it is an extra change, but
doesn't require touching all the callers, etc. Then do the removal in a
follow up patch still.

>
> Philip
>
> (1 inline comment below as well)
>
> On 07/18/2015 02:48 AM, Chandler Carruth wrote:
>
> LLVM and Clang both have lots of objects that are passed through many
> different API boundaries. Things like AliasAnalysis in LLVM or Sema in
> Clang get threaded all over the place.
>
>  Over times, refactoring can often cause the parameters (or local
> variables, or member variables, etc) to become dead. If we notice this, we
> can often un-thread the interface through our APIs, sometimes even reducing
> coupling, etc.
>
>  But currently -Wunused-parameter is hard disabled. I've not checked to
> see if there are any other disabling of -Wunused-* variants, but I'd
like
> to move the project toward firmly enabling them and being clean with them.
>
>  The technique I'd like to use is leaving out names of unused
parameters,
> using a /*CommentedName*/ if there is a useful name, otherwise just
> omitting the name.
>
> Sorry, could you rephrase?  Not sure what you're getting at here.
>
>
>  All of this will require a reasonable amount of cleanup across the
> projects which I'm happy to do prior to flipping defaults around.
Thoughts?
> Any concerns or objections?
>
>  (I'll ask the same question and ofter to either enact the cleanups or
> toggle the warning(s) back off for each of the less intertwined subprojects
> like LLD, LLDB, Polly, etc.)
>
>  -Chandler
>
>
> _______________________________________________
> LLVM Developers mailing listLLVMdev at cs.uiuc.edu        
http://llvm.cs.uiuc.eduhttp://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
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