Mesa (main): nir/lower_tex: Add a lower_txs_cube_array option

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Module: Mesa
Branch: main
Commit: 60b5faf57237a8cb61cabedaedbdfef256d2a9db
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=60b5faf57237a8cb61cabedaedbdfef256d2a9db

Author: Jason Ekstrand <jason at jlekstrand.net>
Date:   Wed Jul 21 16:39:15 2021 -0500

nir/lower_tex: Add a lower_txs_cube_array option

Several bits of hardware require the division by 6 to happen in the
shader.  May as well have common lowering for it.

Reviewed-by: Emma Anholt <emma at anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12005>

---

 src/compiler/nir/nir.h           |  6 ++++++
 src/compiler/nir/nir_lower_tex.c | 26 ++++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index abd1495be9d..76515498c5e 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -4913,6 +4913,12 @@ typedef struct nir_lower_tex_options {
     */
    bool lower_txs_lod;
 
+   /**
+    * If true, lower nir_texop_txs for cube arrays to a nir_texop_txs with a
+    * 2D array type followed by a nir_idiv by 6.
+    */
+   bool lower_txs_cube_array;
+
    /**
     * If true, apply a .bagr swizzle on tg4 results to handle Broadcom's
     * mixed-up tg4 locations.
diff --git a/src/compiler/nir/nir_lower_tex.c b/src/compiler/nir/nir_lower_tex.c
index cf8275c5786..6a47851478f 100644
--- a/src/compiler/nir/nir_lower_tex.c
+++ b/src/compiler/nir/nir_lower_tex.c
@@ -1155,6 +1155,25 @@ nir_lower_txs_lod(nir_builder *b, nir_tex_instr *tex)
    return true;
 }
 
+static void
+nir_lower_txs_cube_array(nir_builder *b, nir_tex_instr *tex)
+{
+   assert(tex->sampler_dim == GLSL_SAMPLER_DIM_CUBE && tex->is_array);
+   tex->sampler_dim = GLSL_SAMPLER_DIM_2D;
+
+   b->cursor = nir_after_instr(&tex->instr);
+
+   assert(tex->dest.is_ssa);
+   assert(tex->dest.ssa.num_components == 3);
+   nir_ssa_def *size = &tex->dest.ssa;
+   size = nir_vec3(b, nir_channel(b, size, 0),
+                      nir_channel(b, size, 1),
+                      nir_idiv(b, nir_channel(b, size, 2),
+                                  nir_imm_int(b, 6)));
+
+   nir_ssa_def_rewrite_uses_after(&tex->dest.ssa, size, size->parent_instr);
+}
+
 static bool
 nir_lower_tex_block(nir_block *block, nir_builder *b,
                     const nir_lower_tex_options *options,
@@ -1346,6 +1365,13 @@ nir_lower_tex_block(nir_block *block, nir_builder *b,
          continue;
       }
 
+      if (options->lower_txs_cube_array && tex->op == nir_texop_txs &&
+          tex->sampler_dim == GLSL_SAMPLER_DIM_CUBE && tex->is_array) {
+         nir_lower_txs_cube_array(b, tex);
+         progress = true;
+         continue;
+      }
+
       /* has to happen after all the other lowerings as the original tg4 gets
        * replaced by 4 tg4 instructions.
        */