[cfe-dev] [LLVMdev] Named register variables GNU-style

[Chandler Carruth]

On Fri, Mar 28, 2014 at 2:31 AM, Renato Golin <renato.golin at linaro.org>wrote:

> On 28 March 2014 02:06, Rafael Espíndola <rafael.espindola at gmail.com>
> wrote:
> > Correct. The proposed solution would work for all non allocatable
> > registers. We should probably still err if someone tries to use an
> > allocatable one.
>
> AFAIK, GCC reserves the allocatable registers. If we're going to do
> this we'd have to be as close as possible to the current behaviour to
> avoid surprises.


This has been the long standing historical objection to the feature. It is
a *really* invasive change to the register allocator to plumb this kind of
register reservation through it. Worse, the semantics for it being
inherently translation-unit based become deeply confusing in LLVM due to
the potential for (partial) LTO.
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