Move createEliminateAvailableExternallyPass earlier

[Teresa Johnson via cfe-commits]

Hi Yaron,

This is to handle the case of pre-built (real .o) files.
The available externally functions are kept in the -c -flto compile
(the pass isn't run) so that they are available for inlining in the
LTO pipeline. If the available externally function is in a pre-built
object file it wouldn't be subject to inlining or other IPO.
A subsequent round of EliminateAvailableExternallyPass during the LTO
pipeline cleans up the copies kept initially. I'm wondering if the
call I placed in the LTO pipeline (in addLateLTOOptimizationPasses)
should similarly be moved earlier, sometime shortly after inlining in
addLTOOptimizationPasses().

Teresa

On Wed, Sep 2, 2015 at 12:02 AM, Yaron Keren <yaron.keren at gmail.com> wrote:
> r246619, thanks!
> About createEliminateAvailableExternallyPass for LTO, I'm missing something.
> At link time, aren't available externally function supposed to be, well,
> available as external linkage? Won't the link fail without these versions?
> if so, why keep the available externally versions at all for LTO instead of
> using the external linkage versions?
>
>
> 2015-09-01 23:56 GMT+03:00 Teresa Johnson <tejohnson at google.com>:
>>
>> Hi Yaron,
>>
>> Thanks, moving it earlier in general seems ok to me. I originally put
>> this right before the GlobalDCE calls because it was somewhat related.
>> I wonder if the createEliminateAvailableExternallyPass call for the
>> LTO pipeline should similarly be moved up closer to inlining, perhaps
>> after any IP alias analysis passes? Hopefully someone more familiar
>> with the passes than I will comment on how early we can do this.
>>
>> Teresa
>>
>> On Tue, Sep 1, 2015 at 1:32 PM, Yaron Keren via cfe-commits
>> <cfe-commits at lists.llvm.org> wrote:
>> > Following the discussion on cfe-dev, this moves
>> > createEliminateAvailableExternallyPass earlier in the pass pipeline to
>> > save
>> > running many ModulePasses on available external functions that are
>> > thrown
>> > away anyhow.
>> >
>> >
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>> >
>>
>>
>>
>> --
>> Teresa Johnson | Software Engineer | tejohnson at google.com | 408-460-2413
>
>



-- 
Teresa Johnson | Software Engineer | tejohnson at google.com | 408-460-2413