[patch] FastISel omitting unused parameters hurts debug info

[David Blaikie]

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
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