[LLVMdev] adding support for -ffixed-<reg>

[Matthew Curtis]

On 10/2/2012 9:36 AM, 陳韋任 (Wei-Ren Chen) wrote:
> On Tue, Oct 02, 2012 at 09:23:27AM -0500, Matthew Curtis wrote:
>> I'm adding support for -ffixed-<reg> for Hexagon and was wondering if I should
>> do it in such a way that other targets get the support as well by default or if
>> a given target back-end should have to explicitly opt-in for support.
>    What "-ffixed-<reg>" does?
>
> Regards,
> chenwj
>

 From the GCC manual 
(http://gcc.gnu.org/onlinedocs/gcc-4.7.2/gcc/Code-Gen-Options.html#index-ffixed-2267)

-ffixed-/reg/

    Treat the register named reg as a fixed register; generated code
    should never refer to it (except perhaps as a stack pointer, frame
    pointer or in some other fixed role).

    reg must be the name of a register. The register names accepted are
    machine-specific and are defined in the REGISTER_NAMES macro in the
    machine description macro file.


Useful when writing kernel code or other low-level code (e.g. a VM) 
where you want to reserve a particular register for your own use.

Matthew C

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation

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