[Mesa-dev] [PATCH 2/2] radeonsi: Implement ddx/ddy on VI using ds_bpermute

[Marek Olšák]

On Sat, Apr 16, 2016 at 8:04 AM, Michel Dänzer <michel at daenzer.net> wrote:
> On 16.04.2016 14:51, Michel Dänzer wrote:
>> On 16.04.2016 11:39, Tom Stellard wrote:
>>> The ds_bpermute instruction allows threads to transfer data directly
>>> to or from the vgprs of other threads.  These instructions use the lds
>>> hardware to transfer data, but do not read or write lds memory.
>>>
>>> DDX BEFORE:                        |  DDX AFTER:
>>>                                    |
>>> v_mbcnt_lo_u32_b32_e64 v2, -1, 0   |  v_mbcnt_lo_u32_b32_e64 v2, -1, 0
>>> v_mbcnt_hi_u32_b32_e64 v2, -1, v2  |  v_mbcnt_hi_u32_b32_e64 v2, -1, v2
>>> v_lshlrev_b32_e32 v4, 2, v2        |  v_and_b32_e32 v2, 0x3ffffffc, v2
>>> v_and_b32_e32 v2, -4, v2           |  v_lshlrev_b32_e32 v2, 2, v2
>>> v_lshlrev_b32_e32 v3, 2, v2        |  ds_bpermute_b32 v3, v2, v0
>>> s_mov_b32 m0, -1                   |  ds_bpermute_b32 v0, v2, v0 offset:4
>>> ds_write_b32 v4, v0                |  s_waitcnt lgkmcnt(0)
>>> s_waitcnt lgkmcnt(0)               |
>>> v_or_b32_e32 v0, 1, v2             |
>>> v_lshlrev_b32_e32 v0, 2, v0        |
>>> ds_read_b32 v1, v3                 |
>>> ds_read_b32 v0, v0                 |
>>> s_waitcnt lgkmcnt(0)               |
>>>                                    |
>>> LDS: 1 blocks                      |  LDS: 0 blocks
>>
>> Nice.
>>
>>
>> Were these intrinsics already available in LLVM 3.6? If not, the old
>> code needs to be kept for backwards compatibility.
>
> I can see now that you're taking care of this for the bpermute
> intrinsic, but AFAICT the mbcnt intrinsics were only added in LLVM 3.8.

How do you feel about increasing the requirement to LLVM 3.8 for Mesa git?

Marek