nir_to_tgsi: Add support for TXP.

This doesn't perfectly emit all the TXPs we might be able to (if you get
any non-TXP-able projectors, that whole sampler dim gets lowered), but it
should be a big boost to i915g.

softpipe shader-db:
total instructions in shared programs: 2953625 -> 2951201 (-0.08%)
instructions in affected programs: 108901 -> 106477 (-2.23%)
total temps in shared programs: 565869 -> 566632 (0.13%)
temps in affected programs: 8922 -> 9685 (8.55%)

i915g shader-db:
total instructions in shared programs: 372570 -> 370254 (-0.62%)
instructions in affected programs: 39825 -> 37509 (-5.82%)
total tex_indirect in shared programs: 11420 -> 11074 (-3.03%)
tex_indirect in affected programs: 913 -> 567 (-37.90%)
LOST:   0
GAINED: 12

Closes: #4984
Reviewed-by: Adam Jackson <ajax@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11912>

src/gallium/auxiliary/nir/nir_to_tgsi.c

@@ -1895,7 +1895,11 @@ ntt_emit_texture(struct ntt_compile *c, nir_tex_instr *instr)
 
    switch (instr->op) {
    case nir_texop_tex:
-      tex_opcode = TGSI_OPCODE_TEX;
+      if (nir_tex_instr_src_size(instr, nir_tex_instr_src_index(instr, nir_tex_src_backend1)) >
+         instr->coord_components + instr->is_shadow)
+         tex_opcode = TGSI_OPCODE_TXP;
+      else
+         tex_opcode = TGSI_OPCODE_TEX;
       break;
    case nir_texop_txf:
    case nir_texop_txf_ms:
@@ -2705,6 +2709,7 @@ nir_to_tgsi_lower_tex_instr(nir_builder *b, nir_instr *instr, void *data)
 
    /* XXX: LZ */
    nir_to_tgsi_lower_tex_instr_arg(b, tex, nir_tex_src_lod, &s);
+   nir_to_tgsi_lower_tex_instr_arg(b, tex, nir_tex_src_projector, &s);
 
    /* No need to pack undefs in unused channels of the tex instr */
    while (!s.channels[s.i - 1])
@@ -2775,6 +2780,45 @@ ntt_fix_nir_options(struct pipe_screen *screen, struct nir_shader *s)
    }
 }
 
+/* Lowers texture projectors if we can't do them as TGSI_OPCODE_TXP. */
+static void
+nir_to_tgsi_lower_txp(nir_shader *s)
+{
+   nir_lower_tex_options lower_tex_options = {
+       .lower_txp = 0,
+   };
+
+   nir_foreach_block(block, nir_shader_get_entrypoint(s)) {
+      nir_foreach_instr(instr, block) {
+         if (instr->type != nir_instr_type_tex)
+            continue;
+         nir_tex_instr *tex = nir_instr_as_tex(instr);
+
+         if (nir_tex_instr_src_index(tex, nir_tex_src_projector) < 0)
+            continue;
+
+         bool has_compare = nir_tex_instr_src_index(tex, nir_tex_src_comparator) >= 0;
+         bool has_lod = nir_tex_instr_src_index(tex, nir_tex_src_lod) >= 0 || s->info.stage != MESA_SHADER_FRAGMENT;
+         bool has_offset = nir_tex_instr_src_index(tex, nir_tex_src_offset) >= 0;
+
+         /* We can do TXP for any tex (not txg) where we can fit all the
+          * coordinates and comparator and projector in one vec4 without any
+          * other modifiers to add on.
+          *
+          * nir_lower_tex() only handles the lowering on a sampler-dim basis, so
+          * if we get any funny projectors then we just blow them all away.
+          */
+         if (tex->op != nir_texop_tex || has_lod || has_offset || (tex->coord_components >= 3 && has_compare))
+            lower_tex_options.lower_txp |= 1 << tex->sampler_dim;
+      }
+   }
+
+   /* nir_lower_tex must be run even if no options are set, because we need the
+    * LOD to be set for query_levels and for non-fragment shaders.
+    */
+   NIR_PASS_V(s, nir_lower_tex, &lower_tex_options);
+}
+
 /**
  * Translates the NIR shader to TGSI.
  *
@@ -2801,12 +2845,7 @@ nir_to_tgsi(struct nir_shader *s,
               type_size, (nir_lower_io_options)0);
    NIR_PASS_V(s, nir_lower_regs_to_ssa);
 
-   const nir_lower_tex_options lower_tex_options = {
-      /* XXX: We could skip lowering of TXP for TEX with <=3 coord_compoennts.
-       */
-      .lower_txp = ~0,
-   };
-   NIR_PASS_V(s, nir_lower_tex, &lower_tex_options);
+   nir_to_tgsi_lower_txp(s);
    NIR_PASS_V(s, nir_to_tgsi_lower_tex);
 
    if (!original_options->lower_uniforms_to_ubo) {

src/gallium/drivers/i915/ci/piglit-i915-g33-fails.txt

@@ -279,7 +279,8 @@ spec@arb_texture_rectangle@glsl-fs-shadow2drectproj,Fail
 spec@arb_texture_rectangle@tex-miplevel-selection gl2:texture() 2drectshadow,Fail
 spec@arb_texture_rectangle@tex-miplevel-selection gl2:textureproj 2drectshadow,Fail
 
-# Too many texture phases, would be avoided if nir_to_tgsi did TXP or if we scheduled.
+# Too many texture phases and regs, because nir_to_tgsi emits MOV TEMP[n],
+# IN[x].xyxw setting up the TXP coords.
 spec@arb_texture_rectangle@texrect-many,Fail
 
 spec@arb_texture_rectangle@texwrap rect bordercolor,Fail