[PATCH] Generate better location ranges for some register-described variables.

[Alexey Samsonov]

On Fri, May 30, 2014 at 12:45 PM, Eric Christopher <echristo at gmail.com>
wrote:

> On Fri, May 30, 2014 at 10:26 AM, Adrian Prantl <aprantl at apple.com> wrote:
> >
> >> On May 29, 2014, at 10:03 PM, Alexey Samsonov <vonosmas at gmail.com>
> wrote:
> >>
> >> Yeah, well, we can add "FrameTeardown" machine instruction flag in
> addition to "FrameSetup", and annotate machine instructions added in frame
> lowering code. But do we expect many users of this flag (assuming that this
> usage is also somewhat questionable)?
> >
> > The FrameSetup flag is also only used by the debug info, so at least it
> wouldn’t be any more questionable than that :-)
>

OK. Why don't we land the patch as-is now (don't terminate the register at
the end of MBB if this register is only modified in frame setup and the
last MBB - it should be safe), and then replace "the last MBB" condition
with
checking a "FrameTeardown" flag, attached to certain machine instructions?
In this way we won't have to special-case certain registers and make
assumptions about their constant-ness.


> >
>
> :)
>
> >> I can also make this patch even less general and just special-case the
> frame pointer and the stack pointer registers, so that the code wouldn't
> pretend to solve a general problem we're facing.
> >
> > The frame pointer should be stable over the entire function, special
> casing it seems to be appropriate. I don’t know whether, e.g, stack
> coloring would cause the stack pointer to be modified in the middle of a
> function.
> >
>
> FWIW it may not _now_ but there's nothing from stopping it either. :\
>
> -eric


-- 
Alexey Samsonov
vonosmas at gmail.com
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