[Mesa-dev] [PATCH v2] i965/fs: Add remove_extra_rounding_modes optimization

[Jason Ekstrand]

On Tue, Aug 29, 2017 at 11:54 PM, Alejandro Piñeiro <apinheiro at igalia.com>
wrote:

> Although from SPIR-V point of view, rounding modes are attached to the
> operation/destination, on i965 it is a status, so we don't need to
> explicitly set the rounding mode if the one we want is already set.
>
> v2: Use a single SHADER_OPCODE_RND_MODE opcode taking an immediate
>     with the rounding mode (Curro)
>
> Signed-off-by: Jose Maria Casanova Crespo <jmcasanova at igalia.com>
> Signed-off-by: Alejandro Piñeiro <apinheiro at igalia.com
>
> ---
>  src/intel/compiler/brw_fs.cpp | 41 ++++++++++++++++++++++++++++++
> +++++++++++
>  src/intel/compiler/brw_fs.h   |  1 +
>  2 files changed, 42 insertions(+)
>
> diff --git a/src/intel/compiler/brw_fs.cpp b/src/intel/compiler/brw_fs.cpp
> index 45236e3cab7..1b9ab0c0b88 100644
> --- a/src/intel/compiler/brw_fs.cpp
> +++ b/src/intel/compiler/brw_fs.cpp
> @@ -3071,6 +3071,46 @@ fs_visitor::remove_duplicate_mrf_writes()
>     return progress;
>  }
>
> +/**
> + * Rounding modes for conversion instructions are included for each
> + * conversion, but right now it is a state. So once it is set,
> + * we don't need to call it again for subsequent calls.
> + *
> + * This is useful for vector/matrices conversions, as setting the
> + * mode once is enough for the full vector/matrix
> + */
> +bool
> +fs_visitor::remove_extra_rounding_modes()
> +{
> +   bool progress = false;
> +   /* By default, the rounding mode is rte, so we can consider it as the
> +    * starting rounding mode
> +    */
> +   brw_rnd_mode prev_mode = BRW_RND_MODE_RTNE;
>

This needs to be reset for every block.  Otherwise, you may end up
invalidly making assumptions about the rounding mode at the start of a loop
or on two sides of an if.  This probably means you should just use
foreach_block and foreach_inst_safe separately.


> +   brw_rnd_mode current_mode;
>

I think I'd prefer this be declared right there in the loop where it's
used.  Maybe make it const and just call it "mode"?


> +
> +   foreach_block_and_inst_safe (block, fs_inst, inst, cfg) {
> +      if (inst->opcode == SHADER_OPCODE_RND_MODE) {
> +         assert(inst->src[0].file == BRW_IMMEDIATE_VALUE);
> +
> +         current_mode = (brw_rnd_mode) inst->src[0].d;
> +
> +         if (current_mode == prev_mode) {
> +            inst->remove(block);
> +            progress = true;
> +         } else {
> +            prev_mode = current_mode;
> +         }
> +      }
> +   }
> +
> +   if (progress)
> +      invalidate_live_intervals();
> +
> +   return progress;
> +}
> +
> +
>  static void
>  clear_deps_for_inst_src(fs_inst *inst, bool *deps, int first_grf, int
> grf_len)
>  {
> @@ -5748,6 +5788,7 @@ fs_visitor::optimize()
>     int pass_num = 0;
>
>     OPT(opt_drop_redundant_mov_to_flags);
> +   OPT(remove_extra_rounding_modes);
>
>     do {
>        progress = false;
> diff --git a/src/intel/compiler/brw_fs.h b/src/intel/compiler/brw_fs.h
> index f1ba193de7e..b9476e69edb 100644
> --- a/src/intel/compiler/brw_fs.h
> +++ b/src/intel/compiler/brw_fs.h
> @@ -150,6 +150,7 @@ public:
>     bool eliminate_find_live_channel();
>     bool dead_code_eliminate();
>     bool remove_duplicate_mrf_writes();
> +   bool remove_extra_rounding_modes();
>
>     bool opt_sampler_eot();
>     bool virtual_grf_interferes(int a, int b);
> --
> 2.11.0
>
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