[LLVMdev] Remove subreg copies

[Ivan Llopard]

Hi Jakob,

Le 28/03/2012 18:51, Jakob Stoklund Olesen a écrit :
> On Mar 28, 2012, at 7:41 AM, Ivan Llopard<ivanllopard at gmail.com>  wrote:
>
>> Hi,
>>
>> I'm facing a problem in my BE while trying to remove certain copies.
>> Here is a code snippet which I would like to optimize
>>
>> %vreg1<def>  = READF32r; vRRegs:%vreg1
>> %vreg2<def>  = COPY %vreg1:rsub_h; iRSubRegs:%vreg2 vRRegs:%vreg1
>> %vreg3<def>  = COPY %vreg1:rsub_l; iRSubRegs:%vreg3 vRRegs:%vreg1
>>
>> This code produces subreg-to-subreg copies but I would like to have
>> direct uses of vreg1's subregisters instead.
>> I tried to add RAhints in order to form identity copies (vreg1 and
>> vreg2/3 should be allocated to the same sub/super register) and let the
>> RA removes them automatically but it didn't work on all the copies. Is
>> there another method to get rid of these copies whenever possible ?
> I assume you are using svn trunk, otherwise I recommend you upgrade.
>
> The output of -debug-only=regalloc should tell you why the register coalescer isn't eliminating the copies.

Thanks ! Looking into the coalescer, I realized I forgot to implement 
the hook getMatchingSuperRegClass(). Now, it works smoothly!

Regards,
Ivan

>
> /jakob
>