Re: GCN: Remove 'FIRST_{SGPR,VGPR,AVGPR}_REG', 'LAST_{SGPR,VGPR,AVGPR}_REG' from machine description

[Andrew Stubbs <ams@baylibre.com>]

On 31/01/2024 17:21, Thomas Schwinge wrote:
> Hi!
> 
> On 2018-12-12T11:52:23+0000, Andrew Stubbs <ams@codesourcery.com> wrote:
>> This patch contains the machine description portion of the GCN back-end.  [...]
> 
>> --- /dev/null
>> +++ b/gcc/config/gcn/gcn.md
> 
>> +;; {{{ Constants and enums
>> +
>> +; Named registers
>> +(define_constants
>> +  [(FIRST_SGPR_REG		 0)
>> +   (LAST_SGPR_REG		 101)
>> +   (FLAT_SCRATCH_REG		 102)
>> +   (FLAT_SCRATCH_LO_REG		 102)
>> +   (FLAT_SCRATCH_HI_REG		 103)
>> +   (XNACK_MASK_REG		 104)
>> +   (XNACK_MASK_LO_REG		 104)
>> +   (XNACK_MASK_HI_REG		 105)
>> +   (VCC_REG			 106)
>> +   (VCC_LO_REG			 106)
>> +   (VCC_HI_REG			 107)
>> +   (VCCZ_REG			 108)
>> +   (TBA_REG			 109)
>> +   (TBA_LO_REG			 109)
>> +   (TBA_HI_REG			 110)
>> +   (TMA_REG			 111)
>> +   (TMA_LO_REG			 111)
>> +   (TMA_HI_REG			 112)
>> +   (TTMP0_REG			 113)
>> +   (TTMP11_REG			 124)
>> +   (M0_REG			 125)
>> +   (EXEC_REG			 126)
>> +   (EXEC_LO_REG			 126)
>> +   (EXEC_HI_REG			 127)
>> +   (EXECZ_REG			 128)
>> +   (SCC_REG			 129)
>> +   (FIRST_VGPR_REG		 160)
>> +   (LAST_VGPR_REG		 415)])
>> +
>> +(define_constants
>> +  [(SP_REGNUM 16)
>> +   (LR_REGNUM 18)
>> +   (AP_REGNUM 416)
>> +   (FP_REGNUM 418)])

Oops, these last two are actually wrong, since AVGPRs were inserted!

> 
> Generally, shouldn't there be a better way, that avoids duplication and
> instead shares such definitions between 'gcn.h' and 'gcn.md'?

I think this is stuff we originally inherited from the Honza's partial 
port and I just never questioned?

If the definitions are unused then it's fine to remove them (I imagine 
the TBA, TMA, and TTMP registers are also unused). Is there something 
about define_constants that is different to external macros? Does it 
affect the mddump? -fdump output? ICE messages? If there's no difference 
then I'm happy with just deleting the lot and use the gcn.h definitions 
exclusively.

> Until that's settled, OK to push the attached
> "GCN: Remove 'FIRST_{SGPR,VGPR,AVGPR}_REG', 'LAST_{SGPR,VGPR,AVGPR}_REG' from machine description"?
> (I assume "still builds" is sufficient validation of this change.)

The patch is OK.

Andrew