[Mesa-dev] [PATCH 2/2] i965/skl: Disable SIMD16 when 3-source instructions are used

[Ilia Mirkin]

On Wed, Mar 4, 2015 at 9:33 AM, Neil Roberts <neil at linux.intel.com> wrote:
> Stepping C0 of Skylake fails when using SIMD16 with 3-source
> instructions (such as MAD). This patch just makes it disable SIMD16 in
> that case.
>
> This implements WaDisableSIMD16On3SrcInstr and fixes ~190 Piglit
> tests.

Just curious -- is this faster than lowering MAD into MUL + ADD but
staying in SIMD16? (Should be fairly easy to implement as a post-RA
fixup I'd think, although not totally familiar with how the i965
compiler works.)

  -ilia

> ---
>  src/mesa/drivers/dri/i965/brw_fs.cpp | 21 +++++++++++++++++++++
>  src/mesa/drivers/dri/i965/brw_fs.h   |  1 +
>  2 files changed, 22 insertions(+)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
> index 533feb4..62f29e5 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
> @@ -3729,6 +3729,26 @@ fs_visitor::fixup_3src_null_dest()
>     }
>  }
>
> +/**
> + * 3-source instructions don't work on Skylake stepping C0. If the revision
> + * isn't known then it will take the safe option and disable it in case it's
> + * C0. Implements WaDisableSIMD16On3SrcInstr.
> + */
> +void
> +fs_visitor::disable_simd16_with_3src()
> +{
> +   if (brw->gen != 9 || (brw->revision != 2 && brw->revision != -1))
> +      return;
> +
> +   foreach_block_and_inst_safe (block, fs_inst, inst, cfg) {
> +      if (inst->is_3src()) {
> +         no16("SIMD16 doesn't work with 3-source instructions on "
> +              "Gen9 stepping C0\n");
> +         return;
> +      }
> +   }
> +}
> +
>  void
>  fs_visitor::allocate_registers()
>  {
> @@ -3910,6 +3930,7 @@ fs_visitor::run_fs()
>        assign_urb_setup();
>
>        fixup_3src_null_dest();
> +      disable_simd16_with_3src();
>        allocate_registers();
>
>        if (failed)
> diff --git a/src/mesa/drivers/dri/i965/brw_fs.h b/src/mesa/drivers/dri/i965/brw_fs.h
> index 70098d8..7091b9f 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs.h
> +++ b/src/mesa/drivers/dri/i965/brw_fs.h
> @@ -196,6 +196,7 @@ public:
>     void setup_payload_gen6();
>     void setup_vs_payload();
>     void fixup_3src_null_dest();
> +   void disable_simd16_with_3src();
>     void assign_curb_setup();
>     void calculate_urb_setup();
>     void assign_urb_setup();
> --
> 1.9.3
>
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