ac/llvm: add use_waterfall_for_divergent_tex_samplers option

GLSL says that indexing in a samplers array should be done with
a dynamically uniform value.

If the app doesn't obey this constraint, it'll get incorrect
results.

But there's one case where the app might be correct and yet
get incorrect result: if 2 consecutive draws are used, with no
state changes in between, the hardware might run them in the
same wave and the app will get incorrect result as-if it was
using non-dynamically uniform index.

To prevent this, this commit takes advantage of the divergence
analysis pass - if the index is marked as divergent, then it will
have the same effect as using ACCESS_NON_UNIFORM in SPIR-V.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16709>

src/amd/llvm/ac_shader_abi.h

@@ -129,6 +129,10 @@ struct ac_shader_abi {
 
    /* Whether to inline the compute dispatch size in user sgprs. */
    bool load_grid_size_from_user_sgpr;
+
+   /* Whether to detect divergent textures/samplers index and apply
+    * waterfall to avoid incorrect rendering. */
+   bool use_waterfall_for_divergent_tex_samplers;
 };
 
 #endif /* AC_SHADER_ABI_H */