[cfe-dev] Just a quick heads up -- removing BBVectorize from LLVM (and Clang)

[Hal Finkel via cfe-dev]

On 06/30/2017 09:01 PM, C Bergström via cfe-dev wrote:
> I don't know how others feel, but it seems this was removed more by 
> feeling and less by actual data points. It doesn't mean it wasn't the 
> correct choice, but just because nobody spoke up could mean that they 
> silently enjoy the benefits and maybe some end user far away isn't 
> subscribed. With this in mind - I hope others would consider turning 
> optimizations into an Assert, Warning or Error if they will be removed 
> - at least for a release.

They'll get a warning about an unused command-line argument. Also, I 
think there's been some discussion about adding a more-specific warning 
for this case.

Thanks again,
Hal

> That way there's some visible warning that users had a chance to see 
> and potentially relay the feedback. The middle ground could be 
> disabling the transformation and just warning on the analysis pass. 
> "Foo optimization has been removed and it may impact your code 
> performance"...
>
> Too much work?
>
> On Sat, Jul 1, 2017 at 9:32 AM, Chandler Carruth via cfe-dev 
> <cfe-dev at lists.llvm.org <mailto:cfe-dev at lists.llvm.org>> wrote:
>
>     Already added in the commit (I think)
>
>     On Fri, Jun 30, 2017 at 3:58 PM Hans Wennborg <hans at chromium.org
>     <mailto:hans at chromium.org>> wrote:
>
>         On Thu, Jun 29, 2017 at 3:42 PM, Chandler Carruth via cfe-dev
>         <cfe-dev at lists.llvm.org <mailto:cfe-dev at lists.llvm.org>> wrote:
>         > If you don't use BBVectorize at all, you can ignore this.
>         >
>         > Hal suggested this in a thread in 2014:
>         >
>         http://lists.llvm.org/pipermail/llvm-dev/2014-November/079091.html
>         <http://lists.llvm.org/pipermail/llvm-dev/2014-November/079091.html>
>         >
>         > None objected then, and I don't think any new uses have
>         arisen so I plan to
>         > just remove it. It is causing maintenance burden,
>         complexity, and is a set
>         > of features I'd rather not port to the new PM.
>         >
>         > Just an FYI email to folks so they aren't confused when the
>         patches land.
>
>         Maybe worth mentioning in the release notes?
>
>
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-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory

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