[LLVMdev] Recent changes in -gmlt break sample profiling

Xinliang David Li xinliangli at gmail.com
Sun Oct 26 16:55:14 PDT 2014

On Sun, Oct 26, 2014 at 3:51 PM, Reid Kleckner <rnk at google.com> wrote:

> On Fri, Oct 24, 2014 at 4:06 PM, Xinliang David Li <xinliangli at gmail.com>
> wrote:
>> Diego,
>> I think sampleFDO needs to be designed in a way which can protect itself
>> from future breakage like this. The roots in the unnecessary dependency of
>> sample FDO on gmlt setting. It is totally reasonable to tune debug binary
>> size by changes like this.
> FWIW, it's not 100% clear to me that this is the right change. Might be
> worth chatting about on Monday.
>> The right way is to fix this is to introduce an internal -g<...> flag for
>> use by sampleFDO -- it will have a fixed definition of what needs to be
>> emitted.
> This doesn't seem worth having an internal flag for. Google is probably
> the primary consumer of Clang's -gline-tables-only data. If it doesn't meet
> our needs, we can lobby to make it behave the way we need it to.

What you propose here works fine if the behavior of -gmlt  satisfies the
need of the optimizer and is well documented with good regression tests:)

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