i965/vec4: Pass const references to vec4_instruction().

text	   data	    bss	    dec	    hex	filename
4244821	 123200	  39648	4407669	 434175	i965_dri.so
4231165	 123200	  39648	4394013	 430c1d	i965_dri.so

Cuts 13k of .text and saves a bunch of useless struct copies.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/brw_vec4.h

@@ -233,10 +233,10 @@ public:
    DECLARE_RALLOC_CXX_OPERATORS(vec4_instruction)
 
    vec4_instruction(vec4_visitor *v, enum opcode opcode,
-		    dst_reg dst = dst_reg(),
-		    src_reg src0 = src_reg(),
-		    src_reg src1 = src_reg(),
-		    src_reg src2 = src_reg());
+                    const dst_reg &dst = dst_reg(),
+                    const src_reg &src0 = src_reg(),
+                    const src_reg &src1 = src_reg(),
+                    const src_reg &src2 = src_reg());
 
    struct brw_reg get_dst(void);
    struct brw_reg get_src(const struct brw_vec4_prog_data *prog_data, int i);

src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp

@@ -30,8 +30,9 @@ extern "C" {
 namespace brw {
 
 vec4_instruction::vec4_instruction(vec4_visitor *v,
-				   enum opcode opcode, dst_reg dst,
-				   src_reg src0, src_reg src1, src_reg src2)
+                                   enum opcode opcode, const dst_reg &dst,
+                                   const src_reg &src0, const src_reg &src1,
+                                   const src_reg &src2)
 {
    this->opcode = opcode;
    this->dst = dst;