[LLVMdev] RFC - Adding an optimization report facility?

[Diego Novillo]

On Fri, Mar 7, 2014 at 9:16 AM, Hal Finkel <hfinkel at anl.gov> wrote:
>
>
> I'd prefer that we not do that; although we can certainly use debugging information to enhance the reporting (to include variable names and the like). I prefer the 'srcloc' on loops solution for two reasons:
>
>  1. It does not force users to include debugging symbols just to get optimization reports and, more importantly,

Neither does -gline-tables-only.  In fact, we could silently turn on
just the generation of src locs and not emit them to the object.

>
>  2. Using srcloc is more accurate: If we include only line table information then we miss column information, and so we can't correctly identify a loop with multiple loops per line (and those that arise from macro expansion). This is a real deal-breaker for me.

We don't need column information.  This situation is why I added dwarf
discriminator support recently.  It doesn't matter if the whole
program is in one line, we will be able to distinguish the location of
the loops via the loop hierarchy and the discriminator values.  This
is similar to how we use discriminators for sample profiling.

I don't want to focus just on loops.  We should be able to do
optimization reports on arbitrary instructions. It's true that we
could limit generation of src locs for major constructs at first, but
I'm not sure it's worth the effort.


Diego.