nir/lower_tex: Make the adding a 0 LOD to nir_op_tex in the VS optional.

This controls the whole lowering of "make tex ops with implicit
derivatives on non-implicit-derivative stages be tex ops with an explicit
lod of 0 instead", but it's really hard to describe that in a git commit
summary.

All existing callers get it added except:
- nir_to_tgsi which didn't want it.
- nouveau, which didn't want it (fixes regressions in shadowcube and
  shadow2darray with NIR, since the shading languages don't expose txl of
  those sampler types and thus it's not supported in HW)
- optional lowering passes in mesa/st (lower_rect, YUV lowering, etc)

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Jason Ekstrand <jason.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16156>

src/compiler/nir/nir.h

@@ -5022,6 +5022,12 @@ typedef struct nir_lower_tex_options {
     */
    bool lower_lod_zero_width;
 
+   /* Turns nir_op_tex and other ops with an implicit derivative, in stages
+    * without implicit derivatives (like the vertex shader) to have an explicit
+    * LOD with a value of 0.
+    */
+   bool lower_invalid_implicit_lod;
+
    /**
     * Payload data to be sent to callback / filter functions.
     */

src/compiler/nir/nir_lower_tex.c

@@ -1480,7 +1480,8 @@ nir_lower_tex_block(nir_block *block, nir_builder *b,
        * use an explicit LOD of 0.
        * But don't touch RECT samplers because they don't have mips.
        */
-      if (nir_tex_instr_has_implicit_derivative(tex) &&
+      if (options->lower_invalid_implicit_lod &&
+          nir_tex_instr_has_implicit_derivative(tex) &&
           tex->sampler_dim != GLSL_SAMPLER_DIM_RECT &&
           !nir_shader_supports_implicit_lod(b->shader)) {
          lower_zero_lod(b, tex);