[llvm-dev] XMMs unused

[Matthias Braun via llvm-dev]

> On Nov 2, 2018, at 5:44 AM, Dangeti Tharun kumar <cs15mtech11002 at iith.ac.in> wrote:
> 
> 
> 
> On Fri, Nov 2, 2018 at 3:31 PM Anton Korobeynikov <anton at korobeynikov.info <mailto:anton at korobeynikov.info>> wrote:
> > Yes, I am compiling for linux system.
> > So the RA will not consider assigning a scratch register to a live range crossing function call, though it may reduce spills?
> Well, it has to spill the register – otherwise it could be clobbered by a call. 
> May be, I haven't conveyed it properly. What I mean was, does the RA make an analysis of spills incurred by using a scratch register and spilled/restored across the call site and by not using the scratch register at all ?

As far as I read the calling conventions for linux/mac there isn't a single callee saved XMM register, so there is not XMM register for which this would work:

%XMMx = ...
callq ...  # <= this may change the value of XMMx
use %XMMx
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