[patch] FastISel omitting unused parameters hurts debug info

[David Blaikie]

[+Eric, since I forgot him on the first mail]

One other avenue that I haven't explored yet is that, perhaps,
something like r182062 might be applicable, which simply retained more
argument frame index information without generating more machine
registers/instructions. I don't know at all if that applies to this
issue, but it did address a similar issue of debug info missing on
unused parameters (PR14575).

On Thu, Jun 6, 2013 at 7:52 PM, David Blaikie <dblaikie at gmail.com> wrote:
> Hi Dan,
>
> Here's the patch we talked about this afternoon - with the equivalent
> change made to the ARM side of fast ISel to match the X86 change I'd
> made. Turns out with the ARM change something does fail -
> CodeGen/ARM/fast-isel-call.ll. So it seems this change isn't neutral
> to codegen. (though I'm not sure how much we need to care deeply about
> the performance of unused parameters?) I assume the source of the
> change is the FIXME immediately proceeding the change to *FastISel.cpp
> - so perhaps this is an acceptable "we'll fix the underlying issue &
> this and some other things will get better".
>
> I was wondering if you had any ideas on how this should be addressed
> (is this acceptable? in which case I should just update the test case
> (though I don't fully understand it yet). I've attached the two .s
> files, with my change (a.s) and without my change (b.s) (around
> r183465) along with the patch itself.
>
> - David