i965/vec4: Use the replicated fdot instruction in NIR

Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Reviewed-by: Eduardo Lima Mitev <elima@igalia.com>

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

@@ -96,6 +96,14 @@ brw_compiler_create(void *mem_ctx, const struct brw_device_info *devinfo)
     */
    nir_options->lower_ffma = true;
    nir_options->lower_sub = true;
+   /* In the vec4 backend, our dpN instruction replicates its result to all
+    * the components of a vec4.  We would like NIR to give us replicated fdot
+    * instructions because it can optimize better for us.
+    *
+    * For the FS backend, it should be lowered away by the scalarizing pass so
+    * we should never see fdot anyway.
+    */
+   nir_options->fdot_replicates = true;
 
    /* We want the GLSL compiler to emit code that uses condition codes */
    for (int i = 0; i < MESA_SHADER_STAGES; i++) {

src/mesa/drivers/dri/i965/brw_vec4_nir.cpp

@@ -1254,17 +1254,17 @@ vec4_visitor::nir_emit_alu(nir_alu_instr *instr)
       inst->predicate = BRW_PREDICATE_NORMAL;
       break;
 
-   case nir_op_fdot2:
+   case nir_op_fdot_replicated2:
       inst = emit(BRW_OPCODE_DP2, dst, op[0], op[1]);
       inst->saturate = instr->dest.saturate;
       break;
 
-   case nir_op_fdot3:
+   case nir_op_fdot_replicated3:
       inst = emit(BRW_OPCODE_DP3, dst, op[0], op[1]);
       inst->saturate = instr->dest.saturate;
       break;
 
-   case nir_op_fdot4:
+   case nir_op_fdot_replicated4:
       inst = emit(BRW_OPCODE_DP4, dst, op[0], op[1]);
       inst->saturate = instr->dest.saturate;
       break;