nir_to_tgsi: Lower FS input array indexing since we don't declare input arrays.

We can't declare input arrays because mesa/st lowers NIR VS output
declarations to elements no matter what, and virgl has depended on
matching array sizes of declarations between producers and consumers.  So,
we have to lower it away (which is fine because hardware drivers will
generally be lowering anyway).

Reviewed-by: Gert Wollny <gert.wollny@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13295>

src/gallium/auxiliary/nir/nir_to_tgsi.c

@@ -3743,6 +3743,18 @@ const void *nir_to_tgsi_options(struct nir_shader *s,
 
    ntt_fix_nir_options(screen, s, options);
 
+   /* Lower array indexing on FS inputs.  Since we don't set
+    * ureg->supports_any_inout_decl_range, the TGSI input decls will be split to
+    * elements by ureg, and so dynamically indexing them would be invalid.
+    * Ideally we would set that ureg flag based on
+    * PIPE_SHADER_CAP_TGSI_ANY_INOUT_DECL_RANGE, but can't due to mesa/st
+    * splitting NIR VS outputs to elements even if the FS doesn't get the
+    * corresponding splitting, and virgl depends on TGSI across link boundaries
+    * having matching declarations.
+    */
+   if (s->info.stage == MESA_SHADER_FRAGMENT)
+      NIR_PASS_V(s, nir_lower_indirect_derefs, nir_var_shader_in, UINT32_MAX);
+
    NIR_PASS_V(s, nir_lower_io, nir_var_shader_in | nir_var_shader_out,
               type_size, (nir_lower_io_options)0);
    NIR_PASS_V(s, nir_lower_regs_to_ssa);