[LLVMdev] Recent changes in -gmlt break sample profiling

[Diego Novillo]

On Fri Oct 24 2014 at 4:06:05 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.


Sure.


> 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.
>

Not so sure. Semantically, -gmlt is exactly what samplefdo needs. Relying
on the subprogram tag for the function itself was an implementation detail.

Adding yet another debug mode that's very much like -gmlt but not quite is
going to be confusing for users.

I *believe* we can reproduce the same behaviour by using the source
location ranges. I'm still not quite sure how, but I've got Eric and David
within smacking distance, so I'll make myself a nuisance until they give me
enough hints.


Diego.
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