[llvm] r204797 - [mips] Add tests for t0-t3 for N32/N64

[Daniel Sanders]

I think I've got to the bottom of this now. There were two documents released at around the same time. The SGI document used t4-t7, while 'MIPS ABIs Described' released shortly afterwards used t0-t3. I'm told that this is likely to have been a transcription error in the MIPS document. However, given that it has gone uncorrected for 12 years (and GAS has implemented it for at least 8 years) it is effectively the standard.

I'm going to deprecate the use of t4-t7 for LLVM 3.5, and remove it for LLVM 3.6.

> -----Original Message-----
> From: Richard Sandiford [mailto:rdsandiford at googlemail.com]
> Sent: 26 March 2014 14:45
> To: Daniel Sanders
> Cc: llvm-commits at cs.uiuc.edu
> Subject: Re: [llvm] r204797 - [mips] Add tests for t0-t3 for N32/N64
> 
> Daniel Sanders <Daniel.Sanders at imgtec.com> writes:
> > The SGI MIPSpro N32 ABI Handbook uses t4-t7 for $12-$15.
> 
> Ah, OK, in that case I was misremembering, sorry.  (I don't have my copies to
> hand here so was writing from memory.)
> 
> So maybe this was originally implemented wrongly in GAS and has just stuck.
> I can see why supporting both makes sense in that case, so sorry for the
> noise...
> 
> Thanks,
> Richard