brw: Limit maximum push UBO ranges to 64 registers in the NIR pass.

anv already does this limiting, since it needs to handle non-UBO push
constants as well.  iris treats everything as a UBO, but doesn't have
a limiter and was relying on the backend to handle it.

Do this in the NIR pass so that we can eliminate the backend code.
It's not necessary for anv, but handling it here is simple and less
error prone for iris, which calls this in a number of places.  We know
we need to limit things to this much; anv can limit more if needed.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/32841>

src/intel/compiler/brw_nir_analyze_ubo_ranges.c

@@ -276,17 +276,27 @@ brw_nir_analyze_ubo_ranges(const struct brw_compiler *compiler,
 
    struct ubo_range_entry *entries = ranges.data;
 
-   /* Return the top 4.
+   /* Return the top 4, limited to the maximum number of push registers.
     *
-    * The backend may need to shrink these ranges to ensure that they
-    * don't exceed the maximum push constant limits.  It can simply drop
-    * the tail of the list, as that's the least valuable portion.  We
-    * unfortunately can't truncate it here, because we don't know what
-    * the backend is planning to do with regular uniforms.
+    * The Vulkan driver sets up additional non-UBO push constants, so it may
+    * need to shrink these ranges further (see anv_nir_compute_push_layout.c).
+    * The OpenGL driver treats legacy uniforms as a UBO, so this is enough.
+    *
+    * To limit further, simply drop the tail of the list, as that's the least
+    * valuable portion.
     */
    const int max_ubos = 4;
    nr_entries = MIN2(nr_entries, max_ubos);
 
+   const unsigned max_push_regs = 64;
+   unsigned total_push_regs = 0;
+
+   for (unsigned i = 0; i < nr_entries; i++) {
+      if (total_push_regs + entries[i].range.length > max_push_regs)
+         entries[i].range.length = max_push_regs - total_push_regs;
+      total_push_regs += entries[i].range.length;
+   }
+
    for (int i = 0; i < nr_entries; i++) {
       out_ranges[i] = entries[i].range;