Mesa (main): v3dv/pipeline: call nir_lower_explicit_io after first nir optimization loop

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Module: Mesa
Branch: main
Commit: 36c547342ac8b41421ec30815bb866210e1457e1
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=36c547342ac8b41421ec30815bb866210e1457e1

Author: Alejandro Piñeiro <apinheiro at igalia.com>
Date:   Thu Mar 10 00:46:48 2022 +0100

v3dv/pipeline: call nir_lower_explicit_io after first nir optimization loop

That is what most others Vulkan drivers do (radv, anv, turnip at
least).

The origin of this change cames from a CTS test where the loop
unrolling converted a ubo index defined inside a loop from constant to
non constant. That is not desiderable on any driver, but a problem on
v3dv, as v3dv doesn't support that case.

Although we initially tried to fix it on the loop unroll, we discarded
that approach, and focused on the existing nir lowerings/optimizations
as this was not happening with other drivers.

We noted that in other drivers this case of a ubo index going from
const to non-const were also happening with nir_lower_explicit_io, but
in that case it was able to be converted back to a const on following
lowerings. The only difference with other drivers is that we were
calling it before the first nir optimization loop.

So this change helps with fixing the following CTS test (for that we
also need to run additional lowerings, which we do in a later patch):
   dEQP-VK.graphicsfuzz.cov-loop-condition-clamp-vec-of-ones

You can get further details on the following issue and RFC merge
request, specially the merge request:
  https://gitlab.freedesktop.org/mesa/mesa/-/issues/6051
  https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15391

We also made some shaderdb stats with our usual Vulkan apps (ue4
demos, quake3, etc):

 Total instructions in shared programs: 125014 -> 124974 (-0.03%)
 instructions in affected programs: 7544 -> 7504 (-0.53%)
 helped: 7
 HURT: 4

 total uniforms in shared programs: 19026 -> 19019 (-0.04%)
 uniforms in affected programs: 514 -> 507 (-1.36%)
 helped: 5
 HURT: 0

 total max-temps in shared programs: 13430 -> 13438 (0.06%)
 max-temps in affected programs: 270 -> 278 (2.96%)
 helped: 0
 HURT: 8

 total sfu-stalls in shared programs: 739 -> 741 (0.27%)
 sfu-stalls in affected programs: 30 -> 32 (6.67%)
 helped: 0
 HURT: 2

 total inst-and-stalls in shared programs: 125753 -> 125715 (-0.03%)
 inst-and-stalls in affected programs: 7685 -> 7647 (-0.49%)
 helped: 7
 HURT: 4

 total nops in shared programs: 8228 -> 8203 (-0.30%)
 nops in affected programs: 546 -> 521 (-4.58%)
 helped: 9
 HURT: 2

Reviewed-by: Iago Toral Quiroga <itoral at igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16986>

---

 src/broadcom/vulkan/v3dv_pipeline.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/src/broadcom/vulkan/v3dv_pipeline.c b/src/broadcom/vulkan/v3dv_pipeline.c
index 0a18d095051..a5d58e07899 100644
--- a/src/broadcom/vulkan/v3dv_pipeline.c
+++ b/src/broadcom/vulkan/v3dv_pipeline.c
@@ -367,14 +367,6 @@ preprocess_nir(nir_shader *nir)
                        });
    }
 
-   NIR_PASS_V(nir, nir_lower_explicit_io,
-              nir_var_mem_push_const,
-              nir_address_format_32bit_offset);
-
-   NIR_PASS_V(nir, nir_lower_explicit_io,
-              nir_var_mem_ubo | nir_var_mem_ssbo,
-              nir_address_format_32bit_index_offset);
-
    NIR_PASS_V(nir, nir_lower_io_to_temporaries,
               nir_shader_get_entrypoint(nir), true, false);
 
@@ -392,6 +384,14 @@ preprocess_nir(nir_shader *nir)
 
    nir_optimize(nir, true);
 
+   NIR_PASS_V(nir, nir_lower_explicit_io,
+              nir_var_mem_push_const,
+              nir_address_format_32bit_offset);
+
+   NIR_PASS_V(nir, nir_lower_explicit_io,
+              nir_var_mem_ubo | nir_var_mem_ssbo,
+              nir_address_format_32bit_index_offset);
+
    NIR_PASS_V(nir, nir_lower_load_const_to_scalar);
 
    /* Lower a bunch of stuff */