[965] Avoid emitting dead code for DPx/math instructions.

The pass1 optimization stage clears out writemasks and registers, but the
instructions themselves are still being processed at this stage, and could
have resulted in them still being emitted.

src/mesa/drivers/dri/i965/brw_wm_emit.c

@@ -504,6 +504,9 @@ static void emit_dp3( struct brw_compile *p,
 		      const struct brw_reg *arg0,
 		      const struct brw_reg *arg1 )
 {
+   if (!(mask & WRITEMASK_XYZW))
+      return; /* Do not emit dead code*/
+
    assert((mask & WRITEMASK_XYZW) == WRITEMASK_X);
 
    brw_MUL(p, brw_null_reg(), arg0[0], arg1[0]);
@@ -521,6 +524,9 @@ static void emit_dp4( struct brw_compile *p,
 		      const struct brw_reg *arg0,
 		      const struct brw_reg *arg1 )
 {
+   if (!(mask & WRITEMASK_XYZW))
+      return; /* Do not emit dead code*/
+
    assert((mask & WRITEMASK_XYZW) == WRITEMASK_X);
 
    brw_MUL(p, brw_null_reg(), arg0[0], arg1[0]);
@@ -539,6 +545,9 @@ static void emit_dph( struct brw_compile *p,
 		      const struct brw_reg *arg0,
 		      const struct brw_reg *arg1 )
 {
+   if (!(mask & WRITEMASK_XYZW))
+      return; /* Do not emit dead code*/
+
    assert((mask & WRITEMASK_XYZW) == WRITEMASK_X);
 
    brw_MUL(p, brw_null_reg(), arg0[0], arg1[0]);
@@ -582,6 +591,9 @@ static void emit_math1( struct brw_compile *p,
 			GLuint mask,
 			const struct brw_reg *arg0 )
 {
+   if (!(mask & WRITEMASK_XYZW))
+      return; /* Do not emit dead code*/
+
    //assert((mask & WRITEMASK_XYZW) == WRITEMASK_X ||
    //	  function == BRW_MATH_FUNCTION_SINCOS);
    
@@ -606,6 +618,9 @@ static void emit_math2( struct brw_compile *p,
 			const struct brw_reg *arg0,
 			const struct brw_reg *arg1)
 {
+   if (!(mask & WRITEMASK_XYZW))
+      return; /* Do not emit dead code*/
+
    assert((mask & WRITEMASK_XYZW) == WRITEMASK_X);
 
    brw_push_insn_state(p);