i965/fs: Support arbitrarily large sampler indices on Broadwell+.

I added support for these on Haswell, but forgot to update the Broadwell
code before landing it.  Partially fixes Piglit's max-samplers test.

v2: Use get_element_ud() consistently, rather than using it for the
    source but using brw_vec1_grf for the destination..

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>

src/mesa/drivers/dri/i965/gen8_fs_generator.cpp

@@ -252,6 +252,23 @@ gen8_fs_generator::generate_tex(fs_inst *ir,
                  brw_imm_ud(ir->texture_offset));
       }
 
+      if (ir->sampler >= 16) {
+         /* The "Sampler Index" field can only store values between 0 and 15.
+          * However, we can add an offset to the "Sampler State Pointer"
+          * field, effectively selecting a different set of 16 samplers.
+          *
+          * The "Sampler State Pointer" needs to be aligned to a 32-byte
+          * offset, and each sampler state is only 16-bytes, so we can't
+          * exclusively use the offset - we have to use both.
+          */
+         gen8_instruction *add =
+            ADD(get_element_ud(src, 3),
+                get_element_ud(brw_vec8_grf(0, 0), 3),
+                brw_imm_ud(16 * (ir->sampler / 16) *
+                           sizeof(gen7_sampler_state)));
+         gen8_set_mask_control(add, BRW_MASK_DISABLE);
+      }
+
       default_state.exec_size = save_exec_size;
    }
 
@@ -263,7 +280,7 @@ gen8_fs_generator::generate_tex(fs_inst *ir,
    gen8_set_src0(brw, inst, src);
    gen8_set_sampler_message(brw, inst,
                             surf_index,
-                            ir->sampler,
+                            ir->sampler % 16,
                             msg_type,
                             rlen,
                             ir->mlen,