i965/fs/nir: fix the number of register written by FS_OPCODE_GET_BUFFER_SIZE

FS_OPCODE_GET_BUFFER_SIZE is calculated with a resinfo's sampler message.

This patch adjusts the number of registers written by the opcode
following what the PRM spec says about the number of registers written
by the SIMD8 and SIMD16's writeback messages for sampler messages.

Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>

1 files changed, 14 insertions, 2 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
index 52d5ad1..73b09f5 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
@@ -2433,16 +2433,28 @@ fs_visitor::nir_emit_intrinsic(const fs_builder &bld, nir_intrinsic_instr *instr
       fs_reg source = fs_reg(0);
 
       int mlen = 1 * reg_width;
+
+      /* A resinfo's sampler message is used to get the buffer size.
+       * The SIMD8's writeback message consists of four registers and
+       * SIMD16's writeback message consists of 8 destination registers
+       * (two per each component), although we are only interested on the
+       * first component, where resinfo returns the buffer size for
+       * SURFTYPE_BUFFER.
+       */
+      int regs_written = 4 * mlen;
       fs_reg src_payload = fs_reg(GRF, alloc.allocate(mlen),
                                   BRW_REGISTER_TYPE_UD);
       bld.LOAD_PAYLOAD(src_payload, &source, 1, 0);
-
+      fs_reg buffer_size = fs_reg(GRF, alloc.allocate(regs_written),
+                                  BRW_REGISTER_TYPE_UD);
       const unsigned index = prog_data->binding_table.ssbo_start + ssbo_index;
-      fs_inst *inst = bld.emit(FS_OPCODE_GET_BUFFER_SIZE, dest,
+      fs_inst *inst = bld.emit(FS_OPCODE_GET_BUFFER_SIZE, buffer_size,
                                src_payload, fs_reg(index));
       inst->header_size = 0;
       inst->mlen = mlen;
+      inst->regs_written = regs_written;
       bld.emit(inst);
+      bld.MOV(retype(dest, buffer_size.type), buffer_size);
 
       brw_mark_surface_used(prog_data, index);
       break;