[LLVMdev] Immediate instructions / register allocator

[David Blaikie]

On Mon, Oct 22, 2012 at 3:38 AM, Jonas Paulsson
<jonas.paulsson at ericsson.com> wrote:
> Hi,
>
>
>
> I tried transforming code that loads an immediate into a virtual register,
> and then uses that virtual register in various ways, into code that uses
> immediate operands instead.

I suspect a concrete example might be helpful in demonstrating the
specific issue.

> To my surprise, this made the register allocator produce worse code in many
> cases. It seems that it is splitting live intervals and spilling more. In
> some cases the code was better.
>
>
>
> I wonder how this could be? Generally, using the immediates directly as
> constant operands should decrease regpressure, right? How could the
> RA-algorithm have been mislead by this?
>
>
>
> Thanks,
>
>
>
> Jonas
>
>
>
>
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