asahi: Set GPR count accurately for background/EOT

Better occupancy, which is especially important when the background shader
does memory access (for reloads). On my 4K monitor, glmark2 -bdesktop fullscreen
from 95fps to 133fps.

At default settings, glmark2 -bterrain from 63fps to 71fps.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19997>

src/asahi/lib/agx_meta.c

@@ -14,7 +14,6 @@ agx_compile_meta_shader(struct agx_meta_cache *cache, nir_shader *shader,
                         struct agx_shader_key *key,
                         struct agx_tilebuffer_layout *tib)
 {
-   struct agx_shader_info info = { 0 };
    struct util_dynarray binary;
    util_dynarray_init(&binary, NULL);
 
@@ -22,9 +21,9 @@ agx_compile_meta_shader(struct agx_meta_cache *cache, nir_shader *shader,
    if (tib)
       agx_nir_lower_tilebuffer(shader, tib);
 
-   agx_compile_shader_nir(shader, key, NULL, &binary, &info);
-
    struct agx_meta_shader *res = rzalloc(cache->ht, struct agx_meta_shader);
+   agx_compile_shader_nir(shader, key, NULL, &binary, &res->info);
+
    res->ptr = agx_pool_upload_aligned_with_bo(&cache->pool, binary.data,
                                               binary.size, 128,
                                               &res->bo);

src/asahi/lib/agx_meta.h

@@ -6,6 +6,7 @@
 #ifndef __AGX_META_H
 #define __AGX_META_H
 
+#include "asahi/compiler/agx_compile.h"
 #include "agx_tilebuffer.h"
 #include "pool.h"
 
@@ -29,6 +30,7 @@ struct agx_meta_key {
 };
 
 struct agx_meta_shader {
+   struct agx_shader_info info;
    struct agx_bo *bo;
    uint32_t ptr;
 };

src/gallium/drivers/asahi/agx_state.c

@@ -1532,7 +1532,7 @@ agx_build_meta(struct agx_batch *batch, bool store, bool partial_render)
       cfg.unk_2 = 0;
    }
 
-   agx_usc_pack(&b, REGISTERS, cfg) cfg.register_count = 256;
+   agx_usc_pack(&b, REGISTERS, cfg) cfg.register_count = shader->info.nr_gprs;
    agx_usc_pack(&b, NO_PRESHADER, cfg);
 
    return agx_usc_fini(&b);