[Mesa-dev] [PATCH 18/22] i965/fs: Add infrastructure for generating CSEL instructions.

[Kenneth Graunke]

On Monday, March 5, 2018 11:17:29 AM PST Ian Romanick wrote:
> On 02/28/2018 12:58 AM, Samuel Iglesias Gonsálvez wrote:
> > On 24/02/18 00:56, Ian Romanick wrote:
> >> From: Kenneth Graunke <kenneth at whitecape.org>
> >>
> >> v2 (idr): Don't allow CSEL with a non-float src2.
> >>
> >> v3 (idr): Add CSEL to fs_inst::flags_written.  Suggested by Matt.
> >>
> >> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> >> Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
> >> ---
> >>  src/intel/compiler/brw_eu.h             |  1 +
> >>  src/intel/compiler/brw_eu_emit.c        |  1 +
> >>  src/intel/compiler/brw_fs.cpp           |  1 +
> >>  src/intel/compiler/brw_fs_builder.h     | 22 +++++++++++++++++++++-
> >>  src/intel/compiler/brw_fs_generator.cpp |  5 +++++
> >>  5 files changed, 29 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/src/intel/compiler/brw_fs_generator.cpp b/src/intel/compiler/brw_fs_generator.cpp
> >> index cd5be05..9157367 100644
> >> --- a/src/intel/compiler/brw_fs_generator.cpp
> >> +++ b/src/intel/compiler/brw_fs_generator.cpp
> >> @@ -1826,6 +1826,11 @@ fs_generator::generate_code(const cfg_t *cfg, int dispatch_width)
> >>        case BRW_OPCODE_SEL:
> >>  	 brw_SEL(p, dst, src[0], src[1]);
> >>  	 break;
> >> +      case BRW_OPCODE_CSEL:
> >> +         brw_set_default_access_mode(p, BRW_ALIGN_16);
> >> +         brw_CSEL(p, dst, src[0], src[1], src[2]);
> >> +         brw_set_default_access_mode(p, BRW_ALIGN_1);
> > 
> > Setting the access mode to ALIGN_1 is not needed, right? It will
> > continue with the next instruction in the loop that sets ALIGN1 at the
> > beginning of the loop.
> 
> This was in Ken's original patch, so I'm not 100% sure.  I've seen this
> pattern around generating some other instructions, so my gut tells me
> that it's done like this to be explicit and more defensive.

Yeah, I don't think it's strictly necessary, but it's probably a good
idea regardless, just to be defensive.  Most instructions should be
align1, and we just want to emit this one instruction in align16.

A more conservative approach still would be to push/set_default/pop.
I think when I wrote this, I was planning on eliminating push/pop, but
that never happened (and probably won't at this point).

I think it's fine as is, or I'd be fine with push/set/pop.
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