[PATCH RFA MIPS] Prohibit vector modes in accumulators

[Moore, Catherine]

> -----Original Message-----
> From: Matthew Fortune [mailto:Matthew.Fortune@imgtec.com]
> Sent: Friday, January 23, 2015 2:51 PM
> To: Robert Suchanek; gcc-patches@gcc.gnu.org
> Cc: Moore, Catherine
> Subject: RE: [PATCH RFA MIPS] Prohibit vector modes in accumulators
> 
> > 2015-01-23  Robert Suchanek  <robert.suchanek@imgtec.com>
> >
> > 	* config/mips/mips.c (mips_hard_regno_mode_ok_p): Prohibit
> > accumulators
> > 	for all vector modes.
> 
> This seems like a genuine bug and although it can only be triggered by
> loongson or paired-single support it probably qualifies for fixing.
> My suspicion is that the switch to LRA since GCC 4.9 may be the reason this
> hasn't been noticed before. Reload seemed better in some cases at
> eliminating bad decisions from IRA so this may have simply never made it
> through reload by fluke.
> 
> I'd like Catherine to review too since we are in stage4 without a reproducible
> test case.
> 

The patch looks reasonable, but I'd like to see a test case that fails before we agree to include for GCC 5.0.