[Mesa-dev] [PATCH 07/17] intel/compiler/fs: Return multiple_instructions_emitted from generate_linterp

[Kenneth Graunke]

On Tuesday, February 20, 2018 9:15:14 PM PST Matt Turner wrote:
> If multiple instructions are emitted, special handling of things like
> conditional mod, saturate, and NoDDClr/NoDDChk need to be performed.
> 
> I noticed that conditional mods were misapplied when adding support for
> Gen11 (in the previous patch). The next patch fixes the same bug in the
> Gen4 LINE/MAC case, though I was not able to trigger it.
> ---
>  src/intel/compiler/brw_fs.h             |  2 +-
>  src/intel/compiler/brw_fs_generator.cpp | 12 +++++++++---
>  2 files changed, 10 insertions(+), 4 deletions(-)

Ugh...I noticed a couple things:

1. Nothing has set multiple_instructions_emitted since May 2016
   (commit 95272f5c7e6914fe8a85a4e37e07f1e8e3634446), which means
   that block of code has been dead for a long time.

2. Nothing in the FS backend sets inst->no_dd_* either.  It looks like
   it was used for general interpolation until July 2016 (commit
   1eef0b73aa323d94d5a080cd1efa81ccacdbd0d2) and for the unlit centroid
   workaround until August 2016 (commit 875341c69b99dea7942a68c9060aa3).
   So, that's also basically dead.

3. You mention saturate, but we don't handle that specially for multiple
   instructions.

4. You didn't handle conditional modifiers in generate_linterp, so...
   if conditional LINTERP is a thing, it's going to be broken.  That
   said, I'm pretty sure it isn't a thing.

Maybe just drop this patch, and instead delete the
multiple_instructions_emitted stuff entirely?  Maybe move no_dd_* back
to the vec4 backend as well?
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