Store r(0) and x(0) in the same location

As part of improving code generation for clang, we want to
eliminate the special variable that stores the content of X
register zero most of the time. In a future, that will allow us
to eliminate the special case of handling r(0) for most
instructions, thus reducing the code size and allow other
simplifcations.

Therefore, in this commit, eliminate the variable that is used
to store r(0) and make r(0) as synonym for x(0). I have chosen
to keep the r(0) define to keep the size of the diff managable.

1 files changed, 7 insertions, 93 deletions

diff --git a/erts/emulator/beam/beam_emu.c b/erts/emulator/beam/beam_emu.c
index 0f9bfa1871..9a34d5f11a 100644
--- a/erts/emulator/beam/beam_emu.c
+++ b/erts/emulator/beam/beam_emu.c
@@ -99,10 +99,7 @@ do {									\
 do {                                     \
   int i_;                                \
   int Arity_ = PC[-1];                   \
-  if (Arity_ > 0) {                      \
-	CHECK_TERM(r(0));                \
-  }                                      \
-  for (i_ = 1; i_ < Arity_; i_++) {      \
+  for (i_ = 0; i_ < Arity_; i_++) {      \
 	CHECK_TERM(x(i_));               \
   }                                      \
 } while (0)
@@ -293,7 +290,7 @@ void** beam_ops;
 #define Ib(N) (N)
 #define x(N) reg[N]
 #define y(N) E[N]
-#define r(N) x##N
+#define r(N) x(N)
 
 /*
  * Makes sure that there are StackNeed + HeapNeed + 1 words available
@@ -309,12 +306,10 @@ void** beam_ops;
      needed = (StackNeed) + 1; \
      if (E - HTOP < (needed + (HeapNeed))) { \
            SWAPOUT; \
-           reg[0] = r(0); \
            PROCESS_MAIN_CHK_LOCKS(c_p); \
            FCALLS -= erts_garbage_collect(c_p, needed + (HeapNeed), reg, (M)); \
            ERTS_VERIFY_UNUSED_TEMP_ALLOC(c_p); \
            PROCESS_MAIN_CHK_LOCKS(c_p); \
-           r(0) = reg[0]; \
            SWAPIN; \
      } \
      E -= needed; \
@@ -363,12 +358,10 @@ void** beam_ops;
     unsigned need = (Nh);                                       		\
     if ((E - HTOP < need) || (MSO(c_p).overhead + (VNh) >= BIN_VHEAP_SZ(c_p))) {\
        SWAPOUT;                                                 		\
-       reg[0] = r(0);                                           		\
        PROCESS_MAIN_CHK_LOCKS(c_p);                             		\
        FCALLS -= erts_garbage_collect(c_p, need, reg, (Live));  		\
        ERTS_VERIFY_UNUSED_TEMP_ALLOC(c_p);					\
        PROCESS_MAIN_CHK_LOCKS(c_p);                             		\
-       r(0) = reg[0];                                           		\
        SWAPIN;                                                  		\
     }                                                           		\
     HEAP_SPACE_VERIFIED(need);                                                  \
@@ -386,12 +379,10 @@ void** beam_ops;
     unsigned need = (Nh);                                       \
     if (E - HTOP < need) {                                      \
        SWAPOUT;                                                 \
-       reg[0] = r(0);                                           \
        PROCESS_MAIN_CHK_LOCKS(c_p);                             \
        FCALLS -= erts_garbage_collect(c_p, need, reg, (Live));  \
        ERTS_VERIFY_UNUSED_TEMP_ALLOC(c_p);			\
        PROCESS_MAIN_CHK_LOCKS(c_p);                             \
-       r(0) = reg[0];                                           \
        SWAPIN;                                                  \
     }                                                           \
     HEAP_SPACE_VERIFIED(need);                             \
@@ -408,15 +399,11 @@ void** beam_ops;
     unsigned need = (Nh);						\
     if (E - HTOP < need) {						\
        SWAPOUT;								\
-       reg[0] = r(0);							\
        reg[Live] = Extra;						\
        PROCESS_MAIN_CHK_LOCKS(c_p);					\
        FCALLS -= erts_garbage_collect(c_p, need, reg, (Live)+1);	\
        ERTS_VERIFY_UNUSED_TEMP_ALLOC(c_p);				\
        PROCESS_MAIN_CHK_LOCKS(c_p);					\
-       if (Live > 0) {							\
-	   r(0) = reg[0];						\
-       }								\
        Extra = reg[Live];						\
        SWAPIN;								\
     }									\
@@ -439,7 +426,6 @@ void** beam_ops;
 #define MakeFun(FunP, NumFree)					\
   do {								\
      SWAPOUT;							\
-     reg[0] = r(0);						\
      r(0) = new_fun(c_p, reg, (ErlFunEntry *) FunP, NumFree);	\
      SWAPIN;							\
   } while (0)
@@ -992,7 +978,6 @@ init_emulator(void)
  */
 
 #if defined(__GNUC__) && defined(sparc) && !defined(DEBUG)
-#  define REG_x0 asm("%l0")
 #  define REG_xregs asm("%l1")
 #  define REG_htop asm("%l2")
 #  define REG_stop asm("%l3")
@@ -1001,7 +986,6 @@ init_emulator(void)
 #  define REG_tmp_arg1 asm("%l6")
 #  define REG_tmp_arg2 asm("%l7")
 #else
-#  define REG_x0
 #  define REG_xregs
 #  define REG_htop
 #  define REG_stop
@@ -1126,11 +1110,6 @@ void process_main(void)
     ERTS_DECLARE_DUMMY(Eterm pid);
 #endif
 
-    /*
-     * X register zero; also called r(0)
-     */
-    register Eterm x0 REG_x0 = NIL;
-
     /* Pointer to X registers: x(1)..x(N); reg[0] is used when doing GC,
      * in all other cases x0 is used.
      */
@@ -1262,7 +1241,7 @@ void process_main(void)
 	int i;
 
 	argp = c_p->arg_reg;
-	for (i = c_p->arity - 1; i > 0; i--) {
+	for (i = c_p->arity - 1; i >= 0; i--) {
 	    reg[i] = argp[i];
 	    CHECK_TERM(reg[i]);
 	}
@@ -1286,12 +1265,6 @@ void process_main(void)
 	}
 
 	next = (BeamInstr *) *I;
-	r(0) = c_p->arg_reg[0];
-#ifdef HARDDEBUG
-	if (c_p->arity > 0) {
-	    CHECK_TERM(r(0));
-	}
-#endif
 	SWAPIN;
 	ASSERT(VALID_INSTR(next));
 
@@ -1365,11 +1338,9 @@ void process_main(void)
 
 	    live = Arg(2);
 	    SWAPOUT;
-	    reg[0] = r(0);
 	    reg[live] = increment_reg_val;
 	    reg[live+1] = make_small(increment_val);
 	    result = erts_gc_mixed_plus(c_p, reg, live);
-	    r(0) = reg[0];
 	    SWAPIN;
 	    ERTS_HOLE_CHECK(c_p);
 	    if (is_value(result)) {
@@ -1383,11 +1354,9 @@ void process_main(void)
     do {                                 \
         Uint live = Arg(1);              \
         SWAPOUT;                         \
-        reg[0] = r(0);                   \
         reg[live] = (Arg1);              \
         reg[live+1] = (Arg2);            \
         result = (Func)(c_p, reg, live); \
-        r(0) = reg[0];                   \
         SWAPIN;                          \
         ERTS_HOLE_CHECK(c_p);            \
         if (is_value(result)) {          \
@@ -1706,7 +1675,6 @@ void process_main(void)
 
      PRE_BIF_SWAPOUT(c_p);
      c_p->fcalls = FCALLS - 1;
-     reg[0] = r(0);
      result = erl_send(c_p, r(0), x(1));
      PreFetch(0, next);
      ERTS_VERIFY_UNUSED_TEMP_ALLOC(c_p);
@@ -1714,7 +1682,6 @@ void process_main(void)
      PROCESS_MAIN_CHK_LOCKS(c_p);
      if (c_p->mbuf || MSO(c_p).overhead >= BIN_VHEAP_SZ(c_p)) {
 	 result = erts_gc_after_bif_call(c_p, result, reg, 2);
-	 r(0) = reg[0];
 	 E = c_p->stop;
      }
      HTOP = HEAP_TOP(c_p);
@@ -1727,7 +1694,6 @@ void process_main(void)
 	 SET_CP(c_p, I+1);
 	 SET_I(c_p->i);
 	 SWAPIN;
-	 r(0) = reg[0];
 	 Dispatch();
      }
      goto find_func_info;
@@ -1935,13 +1901,11 @@ void process_main(void)
      ErtsMoveMsgAttachmentIntoProc(msgp, c_p, E, HTOP, FCALLS,
 				   {
 				       SWAPOUT;
-				       reg[0] = r(0);
 				       PROCESS_MAIN_CHK_LOCKS(c_p);
 				   },
 				   {
 				       ERTS_VERIFY_UNUSED_TEMP_ALLOC(c_p);
 				       PROCESS_MAIN_CHK_LOCKS(c_p);
-				       r(0) = reg[0];
 				       SWAPIN;
 				   });
      if (is_non_value(ERL_MESSAGE_TERM(msgp))) {
@@ -2448,11 +2412,9 @@ void process_main(void)
  OpCase(new_map_dII): {
      Eterm res;
 
-     x(0) = r(0);
      SWAPOUT;
      res = new_map(c_p, reg, I-1);
      SWAPIN;
-     r(0) = x(0);
      StoreResult(res, Arg(0));
      Next(3+Arg(2));
  }
@@ -2543,12 +2505,10 @@ do {								\
      Eterm map;
 
      GetArg1(1, map);
-     x(0) = r(0);
      SWAPOUT;
      res = update_map_assoc(c_p, reg, map, I);
      SWAPIN;
      if (is_value(res)) {
-	 r(0) = x(0);
 	 StoreResult(res, Arg(2));
 	 Next(5+Arg(4));
      } else {
@@ -2567,12 +2527,10 @@ do {								\
      Eterm map;
 
      GetArg1(1, map);
-     x(0) = r(0);
      SWAPOUT;
      res = update_map_exact(c_p, reg, map, I);
      SWAPIN;
      if (is_value(res)) {
-	 r(0) = x(0);
 	 StoreResult(res, Arg(2));
 	 Next(5+Arg(4));
      } else {
@@ -2659,7 +2617,6 @@ do {								\
 	Uint live = (Uint) Arg(3);
 
 	GetArg1(2, arg);
-	reg[0] = r(0);
 	reg[live] = arg;
 	bf = (GcBifFunction) Arg(1);
 	c_p->fcalls = FCALLS;
@@ -2671,7 +2628,6 @@ do {								\
 	ERTS_SMP_REQ_PROC_MAIN_LOCK(c_p);
 	PROCESS_MAIN_CHK_LOCKS(c_p);
 	SWAPIN;
-	r(0) = reg[0];
 	ERTS_HOLE_CHECK(c_p);
 	FCALLS = c_p->fcalls;
 	if (is_value(result)) {
@@ -2694,7 +2650,6 @@ do {								\
 	Eterm result;
 	Uint live = (Uint) Arg(2);
 
-	reg[0] = r(0);
 	reg[live++] = tmp_arg1;
 	reg[live] = tmp_arg2;
 	bf = (GcBifFunction) Arg(1);
@@ -2707,7 +2662,6 @@ do {								\
 	ERTS_SMP_REQ_PROC_MAIN_LOCK(c_p);
 	PROCESS_MAIN_CHK_LOCKS(c_p);
 	SWAPIN;
-	r(0) = reg[0];
 	ERTS_HOLE_CHECK(c_p);
 	FCALLS = c_p->fcalls;
 	if (is_value(result)) {
@@ -2732,7 +2686,6 @@ do {								\
 	Uint live = (Uint) Arg(3);
 
 	GetArg1(2, arg);
-	reg[0] = r(0);
 	reg[live++] = arg;
 	reg[live++] = tmp_arg1;
 	reg[live] = tmp_arg2;
@@ -2746,7 +2699,6 @@ do {								\
 	ERTS_SMP_REQ_PROC_MAIN_LOCK(c_p);
 	PROCESS_MAIN_CHK_LOCKS(c_p);
 	SWAPIN;
-	r(0) = reg[0];
 	ERTS_HOLE_CHECK(c_p);
 	FCALLS = c_p->fcalls;
 	if (is_value(result)) {
@@ -2835,7 +2787,6 @@ do {								\
 	PreFetch(1, next);
 	ASSERT(!ERTS_PROC_IS_EXITING(c_p));
 	ERTS_VERIFY_UNUSED_TEMP_ALLOC(c_p);
-	reg[0] = r(0);
 	result = (*bf)(c_p, reg, I);
 	ASSERT(!ERTS_PROC_IS_EXITING(c_p) || is_non_value(result));
 	ERTS_VERIFY_UNUSED_TEMP_ALLOC(c_p);
@@ -2857,7 +2808,6 @@ do {								\
 	    SET_CP(c_p, I+2);
 	    SET_I(c_p->i);
 	    SWAPIN;
-	    r(0) = reg[0];
 	    Dispatch();
 	}
 
@@ -2967,11 +2917,9 @@ do {								\
      Uint live = Arg(1);
 
      SWAPOUT;
-     reg[0] = r(0);
      reg[live] = tmp_arg1;
      reg[live+1] = tmp_arg2;
      result = arith_func(c_p, reg, live);
-     r(0) = reg[0];
      SWAPIN;
      ERTS_HOLE_CHECK(c_p);
      if (is_value(result)) {
@@ -3166,10 +3114,8 @@ do {								\
      } else {
 	 Uint live = Arg(2);
 	 SWAPOUT;
-	 reg[0] = r(0);
 	 reg[live] = bnot_val;
 	 bnot_val = erts_gc_bnot(c_p, reg, live);
-	 r(0) = reg[0];
 	 SWAPIN;
 	 ERTS_HOLE_CHECK(c_p);
 	 if (is_nil(bnot_val)) {
@@ -3189,7 +3135,6 @@ do {								\
      next = apply(c_p, r(0), x(1), x(2), reg);
      SWAPIN;
      if (next != NULL) {
-	 r(0) = reg[0];
 	 SET_CP(c_p, I+1);
 	 SET_I(next);
 	 Dispatch();
@@ -3204,7 +3149,6 @@ do {								\
      next = apply(c_p, r(0), x(1), x(2), reg);
      SWAPIN;
      if (next != NULL) {
-	 r(0) = reg[0];
 	 SET_CP(c_p, (BeamInstr *) E[0]);
 	 E = ADD_BYTE_OFFSET(E, Arg(0));
 	 SET_I(next);
@@ -3220,7 +3164,6 @@ do {								\
      next = apply(c_p, r(0), x(1), x(2), reg);
      SWAPIN;
      if (next != NULL) {
-	 r(0) = reg[0];
 	 SET_I(next);
 	 Dispatch();
      }
@@ -3231,12 +3174,10 @@ do {								\
  OpCase(apply_I): {
      BeamInstr *next;
 
-     reg[0] = r(0);
      SWAPOUT;
      next = fixed_apply(c_p, reg, Arg(0));
      SWAPIN;
      if (next != NULL) {
-	 r(0) = reg[0];
 	 SET_CP(c_p, I+2);
 	 SET_I(next);
 	 Dispatch();
@@ -3248,12 +3189,10 @@ do {								\
  OpCase(apply_last_IP): {
      BeamInstr *next;
 
-     reg[0] = r(0);
      SWAPOUT;
      next = fixed_apply(c_p, reg, Arg(0));
      SWAPIN;
      if (next != NULL) {
-	 r(0) = reg[0];
 	 SET_CP(c_p, (BeamInstr *) E[0]);
 	 E = ADD_BYTE_OFFSET(E, Arg(1));
 	 SET_I(next);
@@ -3270,7 +3209,6 @@ do {								\
      next = apply_fun(c_p, r(0), x(1), reg);
      SWAPIN;
      if (next != NULL) {
-	 r(0) = reg[0];
 	 SET_CP(c_p, I+1);
 	 SET_I(next);
 	 Dispatchfun();
@@ -3285,7 +3223,6 @@ do {								\
      next = apply_fun(c_p, r(0), x(1), reg);
      SWAPIN;
      if (next != NULL) {
-	 r(0) = reg[0];
 	 SET_CP(c_p, (BeamInstr *) E[0]);
 	 E = ADD_BYTE_OFFSET(E, Arg(0));
 	 SET_I(next);
@@ -3301,7 +3238,6 @@ do {								\
      next = apply_fun(c_p, r(0), x(1), reg);
      SWAPIN;
      if (next != NULL) {
-	 r(0) = reg[0];
 	 SET_I(next);
 	 Dispatchfun();
      }
@@ -3312,12 +3248,9 @@ do {								\
      BeamInstr *next;
 
      SWAPOUT;
-     reg[0] = r(0);
-
      next = call_fun(c_p, Arg(0), reg, THE_NON_VALUE);
      SWAPIN;
      if (next != NULL) {
-	 r(0) = reg[0];
 	 SET_CP(c_p, I+2);
 	 SET_I(next);
 	 Dispatchfun();
@@ -3329,11 +3262,9 @@ do {								\
      BeamInstr *next;
 
      SWAPOUT;
-     reg[0] = r(0);
      next = call_fun(c_p, Arg(0), reg, THE_NON_VALUE);
      SWAPIN;
      if (next != NULL) {
-	r(0) = reg[0];
 	SET_CP(c_p, (BeamInstr *) E[0]);
 	E = ADD_BYTE_OFFSET(E, Arg(1));
 	SET_I(next);
@@ -3418,10 +3349,9 @@ do {								\
       */
 
      argp = c_p->arg_reg;
-     for (i = c_p->arity - 1; i > 0; i--) {
+     for (i = c_p->arity - 1; i >= 0; i--) {
 	 argp[i] = reg[i];
      }
-     c_p->arg_reg[0] = r(0);
      SWAPOUT;
      c_p->i = I;
      goto do_schedule1;
@@ -3531,7 +3461,6 @@ do {								\
  /* Fall through here */
 
  find_func_info: {
-     reg[0] = r(0);
      SWAPOUT;
      I = handle_error(c_p, I, reg, NULL);
      goto post_error_handling;
@@ -3549,9 +3478,7 @@ do {								\
      * code[4]: Not used
      */
     SWAPOUT;
-    reg[0] = r(0);
     I = call_error_handler(c_p, I-3, reg, am_undefined_function);
-    r(0) = reg[0];
     SWAPIN;
     if (I) {
 	Goto(*I);
@@ -3560,14 +3487,12 @@ do {								\
  /* Fall through */
  OpCase(error_action_code): {
     handle_error:
-     reg[0] = r(0);
      SWAPOUT;
      I = handle_error(c_p, NULL, reg, NULL);
  post_error_handling:
      if (I == 0) {
 	 goto do_schedule;
      } else {
-	 r(0) = reg[0];
 	 ASSERT(!is_value(r(0)));
 	 if (c_p->mbuf) {
 	     erts_garbage_collect(c_p, 0, reg+1, 3);
@@ -3610,7 +3535,6 @@ do {								\
 		NifF* fp = vbf = (NifF*) I[1];
 		struct enif_environment_t env;
 		erts_pre_nif(&env, c_p, (struct erl_module_nif*)I[2]);
-		reg[0] = r(0);
 		nif_bif_result = (*fp)(&env, bif_nif_arity, reg);
 		if (env.exception_thrown)
 		    nif_bif_result = THE_NON_VALUE;
@@ -3649,7 +3573,7 @@ do {								\
 	    bif_nif_arity = I[-1];
             ASSERT(bif_nif_arity <= 4);
 	    ERTS_SMP_UNREQ_PROC_MAIN_LOCK(c_p);
-	    reg[0] = r(0);
+	    ERTS_VERIFY_UNUSED_TEMP_ALLOC(c_p);
 	    {
 		Eterm (*bf)(Process*, Eterm*, BeamInstr*) = vbf;
 		ASSERT(!ERTS_PROC_IS_EXITING(c_p));
@@ -3679,7 +3603,6 @@ do {								\
 		Goto(*I);
 	    } else if (c_p->freason == TRAP) {
 		SET_I(c_p->i);
-		r(0) = reg[0];
 		if (c_p->flags & F_HIBERNATE_SCHED) {
 		    c_p->flags &= ~F_HIBERNATE_SCHED;
 		    goto do_schedule;
@@ -4126,10 +4049,8 @@ do {								\
      Uint res;
 
      SWAPOUT;
-     reg[0] = r(0);
      reg[live] = tmp_arg2;
      res = erts_bs_append(c_p, reg, live, tmp_arg1, Arg(1), Arg(3));
-     r(0) = reg[0];
      SWAPIN;
      if (is_non_value(res)) {
 	 /* c_p->freason is already set (may be either BADARG or SYSTEM_LIMIT). */
@@ -4706,7 +4627,7 @@ do {								\
      Uint hole_size;
 
      OpCase(bs_context_to_binary_r): {
-	 context_to_binary_context = x0;
+	 context_to_binary_context = r(0);
 	 I -= 2;
 	 goto do_context_to_binary;
      }
@@ -4737,7 +4658,7 @@ do {								\
      Next(2);
 
      OpCase(i_bs_get_binary_all_reuse_rfI): {
-	 context_to_binary_context = x0;
+	 context_to_binary_context = r(0);
 	 goto do_bs_get_binary_all_reuse;
      }
 
@@ -4883,9 +4804,7 @@ do {								\
      BeamInstr real_I;
      ASSERT(I[-5] == (BeamInstr) BeamOp(op_i_func_info_IaaI));
      SWAPOUT;
-     reg[0] = r(0);
      real_I = erts_generic_breakpoint(c_p, I, reg);
-     r(0) = reg[0];
      SWAPIN;
      ASSERT(VALID_INSTR(real_I));
      Goto(real_I);
@@ -5103,7 +5022,6 @@ do {								\
      SWAPOUT;
      c_p->fcalls = FCALLS;
      c_p->def_arg_reg[4] = -neg_o_reds;
-     reg[0] = r(0);
      c_p = hipe_mode_switch(c_p, cmd, reg);
      reg = ERTS_PROC_GET_SCHDATA(c_p)->x_reg_array;
      freg = ERTS_PROC_GET_SCHDATA(c_p)->f_reg_array;
@@ -5120,7 +5038,6 @@ do {								\
 	 /*fall through*/
        case HIPE_MODE_SWITCH_RES_CALL_BEAM:
 	 SET_I(c_p->i);
-	 r(0) = reg[0];
 	 Dispatch();
        case HIPE_MODE_SWITCH_RES_CALL_CLOSURE:
 	 /* This can be used to call any function value, but currently it's
@@ -5131,7 +5048,6 @@ do {								\
 	     next = call_fun(c_p, c_p->arity - 1, reg, THE_NON_VALUE);
 	     SWAPIN;
 	     if (next != NULL) {
-		 r(0) = reg[0];
 		 SET_I(next);
 		 Dispatchfun();
 	     }
@@ -5191,9 +5107,7 @@ do {								\
 
  OpCase(i_debug_breakpoint): {
      SWAPOUT;
-     reg[0] = r(0);
      I = call_error_handler(c_p, I-3, reg, am_breakpoint);
-     r(0) = reg[0];
      SWAPIN;
      if (I) {
 	 Goto(*I);