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Re: Fix PR44281 (bad RA with global regs)


On 02/29/2016 08:18 AM, Richard Biener wrote:
On Mon, Feb 29, 2016 at 2:38 PM, Bernd Schmidt <bschmidt@redhat.com> wrote:
On 02/27/2016 08:12 PM, Richard Biener wrote:



Am Freitag, 26. Februar 2016 schrieb Jeff Law :

     The other case that came to mind was signal handlers.  What happens
     if we're using the global register as a scratch, we hit a memory
     reference that faults and inside the signal handler the original
     code expects to be able to use the global register the user set up?

     If that's a valid use scenario, then there's probably all kinds of
     DF stuff that we'd need to expose.

I'd say that's a valid assumption.  Though maybe we want to be able to
change semantics with a flag here.


A flag seems like overkill, I don't think people are likely to enable that
ever.

So what's the consensus here, closed wontfix?

I think so, and maybe update documentation to reflect the discussion.
Agreed (closed/wontfix). I think the signal handler case essentially kills the ability to use global regs as scratches.

We could create another style declaration for a global-like register which has different semantics, but I don't think that's wise.

I'd either add a comment summarizing the discussion or a pointer back to the discussion in the archives.

jeff


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