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File 3851-emulator-Remove-vestiges-of-special-handling-of-x-0.patch of Package erlang (Revision 54461a2357af3de1f765489d2fd0ee14)

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From f53c6f4fc8da66fadd90f6a2d85b317cc52641e8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Sat, 10 Jun 2023 13:21:55 +0200
Subject: [PATCH] emulator: Remove vestiges of special handling of x(0)

In the BEAM emulator, X register 0 (`x(0)`) used to be specially
handled by the macro `r(0)` so that it could be placed in a CPU
register.

That made sense for platforms with many registers such as Sparc and
PowerPC. For the register-starved x86_64 platform it is not possible
to allocate a CPU register for `x(0)`. Therefore, in
1f996cc46a8c93 (part of Erlang/OTP 19), the special handling of `x(0)`
was removed. Removing that special case simplified the code in many
places.

Get rid of the vestiges of the special handling of `x(0)`. While at
it, also re-introduce the `REG_xregs` attribute for the variable
holding the pointer to the X registers.
---
 erts/emulator/beam/beam_common.h        |  1 -
 erts/emulator/beam/emu/beam_emu.c       |  8 ++++----
 erts/emulator/beam/emu/bif_instrs.tab   | 22 +++++++++++-----------
 erts/emulator/beam/emu/bs_instrs.tab    |  2 +-
 erts/emulator/beam/emu/instrs.tab       | 16 ++++++++--------
 erts/emulator/beam/emu/msg_instrs.tab   |  2 +-
 erts/emulator/beam/emu/trace_instrs.tab |  6 +++---
 erts/emulator/utils/beam_makeops        |  2 +-
 8 files changed, 29 insertions(+), 30 deletions(-)

diff --git a/erts/emulator/beam/beam_common.h b/erts/emulator/beam/beam_common.h
index ee7a41c9b8..3c93d580a6 100644
--- a/erts/emulator/beam/beam_common.h
+++ b/erts/emulator/beam/beam_common.h
@@ -111,7 +111,6 @@ do {									\
 
 #define x(N) reg[N]
 #define y(N) E[N]
-#define r(N) x(N)
 #define Q(N) (N*sizeof(Eterm *))
 #define l(N) (freg[N].fd)
 
diff --git a/erts/emulator/beam/emu/beam_emu.c b/erts/emulator/beam/emu/beam_emu.c
index 0c91c1ec83..c2081ab3d0 100644
--- a/erts/emulator/beam/emu/beam_emu.c
+++ b/erts/emulator/beam/emu/beam_emu.c
@@ -266,10 +266,10 @@ void process_main(ErtsSchedulerData *esdp)
     ERTS_DECLARE_DUMMY(Eterm pid);
 #endif
 
-    /* Pointer to X registers: x(1)..x(N); reg[0] is used when doing GC,
-     * in all other cases x0 is used.
+    /*
+     * Pointer to X registers: x(0)..x(N).
      */
-    register Eterm* reg = NULL;
+    register Eterm* reg REG_xregs = NULL;
 
     /*
      * Top of heap (next free location); grows upwards.
@@ -552,7 +552,7 @@ void process_main(ErtsSchedulerData *esdp)
      if (I == 0) {
 	 goto do_schedule;
      } else {
-	 ASSERT(!is_value(r(0)));
+	 ASSERT(!is_value(x(0)));
 	 SWAPIN;
 	 Goto(*I);
      }
diff --git a/erts/emulator/beam/emu/bif_instrs.tab b/erts/emulator/beam/emu/bif_instrs.tab
index d1ec68168a..ef26fd4756 100644
--- a/erts/emulator/beam/emu/bif_instrs.tab
+++ b/erts/emulator/beam/emu/bif_instrs.tab
@@ -281,8 +281,8 @@ call_light_bif(Bif, Exp) {
     }
     ERTS_MSACC_SET_STATE_CACHED_M_X(ERTS_MSACC_STATE_EMULATOR);
     if (ERTS_LIKELY(is_value(result))) {
-        r(0) = result;
-        CHECK_TERM(r(0));
+        x(0) = result;
+        CHECK_TERM(x(0));
         $NEXT0();
     } else if (c_p->freason == TRAP) {
         /*
@@ -385,8 +385,8 @@ call_light_bif_only(Bif, Exp) {
         /*
          * Success. Store the result and return to the caller.
          */
-        r(0) = result;
-        CHECK_TERM(r(0));
+        x(0) = result;
+        CHECK_TERM(x(0));
         $return();
     } else if (c_p->freason == TRAP) {
         /*
@@ -426,15 +426,15 @@ send() {
 
     PRE_BIF_SWAPOUT(c_p);
     c_p->fcalls = FCALLS - 1;
-    result = erl_send(c_p, r(0), x(1));
+    result = erl_send(c_p, x(0), x(1));
     ERTS_VERIFY_UNUSED_TEMP_ALLOC(c_p);
     ERTS_REQ_PROC_MAIN_LOCK(c_p);
     PROCESS_MAIN_CHK_LOCKS(c_p);
     HTOP = HEAP_TOP(c_p);
     FCALLS = c_p->fcalls;
     if (ERTS_LIKELY(is_value(result))) {
-        r(0) = result;
-        CHECK_TERM(r(0));
+        x(0) = result;
+        CHECK_TERM(x(0));
     } else if (c_p->freason == TRAP) {
         $SAVE_CONTINUATION_POINTER($NEXT_INSTRUCTION);
         SET_I(c_p->i);
@@ -605,8 +605,8 @@ nif_bif.epilogue() {
     FCALLS = c_p->fcalls;
     ERTS_DBG_CHK_REDS(c_p, FCALLS);
     if (ERTS_LIKELY(is_value(nif_bif_result))) {
-        r(0) = nif_bif_result;
-        CHECK_TERM(r(0));
+        x(0) = nif_bif_result;
+        CHECK_TERM(x(0));
         $RETURN();
         Goto(*I);
     } else if (c_p->freason == TRAP) {
@@ -632,13 +632,13 @@ i_load_nif() {
         Eterm result;
 
         PRE_BIF_SWAPOUT(c_p);
-        result = erts_load_nif(c_p, I, r(0), r(1));
+        result = erts_load_nif(c_p, I, x(0), x(1));
         erts_release_code_mod_permission();
         ERTS_REQ_PROC_MAIN_LOCK(c_p);
         SWAPIN;
 
         if (ERTS_LIKELY(is_value(result))) {
-            r(0) = result;
+            x(0) = result;
             $NEXT0();
         } else {
             static ErtsCodeMFA mfa = {am_erlang, am_load_nif, 2};
diff --git a/erts/emulator/beam/emu/bs_instrs.tab b/erts/emulator/beam/emu/bs_instrs.tab
index a42c2eb331..9a1360c26e 100644
--- a/erts/emulator/beam/emu/bs_instrs.tab
+++ b/erts/emulator/beam/emu/bs_instrs.tab
@@ -738,7 +738,7 @@ i_bs_private_append(Fail, Unit, Size, Src, Dst) {
 
 bs_init_writable() {
     HEAVY_SWAPOUT;
-    r(0) = erts_bs_init_writable(c_p, r(0));
+    x(0) = erts_bs_init_writable(c_p, x(0));
     HEAVY_SWAPIN;
 }
 
diff --git a/erts/emulator/beam/emu/instrs.tab b/erts/emulator/beam/emu/instrs.tab
index 88e6da9bf1..e675eadf99 100644
--- a/erts/emulator/beam/emu/instrs.tab
+++ b/erts/emulator/beam/emu/instrs.tab
@@ -311,7 +311,7 @@ apply_last(Arity, Deallocate) {
 
 APPLY_FUN(Next) {
     HEAVY_SWAPOUT;
-    $Next = apply_fun(c_p, r(0), x(1), reg);
+    $Next = apply_fun(c_p, x(0), x(1), reg);
     HEAVY_SWAPIN;
 
     if (ERTS_UNLIKELY(next == NULL)) {
@@ -378,7 +378,7 @@ return() {
     //| -no_next
     DTRACE_RETURN_FROM_PC(c_p, I);
     $RETURN();
-    CHECK_TERM(r(0));
+    CHECK_TERM(x(0));
     HEAP_SPACE_VERIFIED(0);
 
     $DISPATCH_RETURN();
@@ -1129,11 +1129,11 @@ catch_end(Y) {
      *    x3 = Exception class
      */
     $try_end($Y);
-    if (is_non_value(r(0))) {
+    if (is_non_value(x(0))) {
         ASSERT(c_p->fvalue == NIL);
         ASSERT(c_p->ftrace == NIL);
         if (x(3) == am_throw) {
-            r(0) = x(1);
+            x(0) = x(1);
         } else {
             if (x(3) == am_error) {
                 SWAPOUT;
@@ -1150,11 +1150,11 @@ catch_end(Y) {
                 SWAPIN;
                 $MAYBE_EXIT_AFTER_GC();
             }
-            r(0) = TUPLE2(HTOP, am_EXIT, x(1));
+            x(0) = TUPLE2(HTOP, am_EXIT, x(1));
             HTOP += 3;
         }
     }
-    CHECK_TERM(r(0));
+    CHECK_TERM(x(0));
 }
 
 try_end(Y) {
@@ -1164,10 +1164,10 @@ try_end(Y) {
 
 try_case(Y) {
     $try_end($Y);
-    ASSERT(is_non_value(r(0)));
+    ASSERT(is_non_value(x(0)));
     ASSERT(c_p->fvalue == NIL);
     ASSERT(c_p->ftrace == NIL);
-    r(0) = x(3);
+    x(0) = x(3);
 }
 
 try_case_end(Src) {
diff --git a/erts/emulator/beam/emu/msg_instrs.tab b/erts/emulator/beam/emu/msg_instrs.tab
index ef733ae80a..00c7291257 100644
--- a/erts/emulator/beam/emu/msg_instrs.tab
+++ b/erts/emulator/beam/emu/msg_instrs.tab
@@ -136,7 +136,7 @@ i_loop_rec(Dest) {
     ASSERT(msgp == erts_msgq_peek_msg(c_p));
     ASSERT(ERTS_SIG_IS_INTERNAL_MSG(msgp));
 
-    r(0) = ERL_MESSAGE_TERM(msgp);
+    x(0) = ERL_MESSAGE_TERM(msgp);
 }
 
 remove_message() {
diff --git a/erts/emulator/beam/emu/trace_instrs.tab b/erts/emulator/beam/emu/trace_instrs.tab
index 9b0b377ed7..14ac98a311 100644
--- a/erts/emulator/beam/emu/trace_instrs.tab
+++ b/erts/emulator/beam/emu/trace_instrs.tab
@@ -24,7 +24,7 @@ return_trace() {
 
     SWAPOUT;		/* Needed for shared heap */
     ERTS_UNREQ_PROC_MAIN_LOCK(c_p);
-    erts_trace_return(c_p, mfa, r(0), ERTS_TRACER_FROM_ETERM(E+2)/* tracer */);
+    erts_trace_return(c_p, mfa, x(0), ERTS_TRACER_FROM_ETERM(E+2)/* tracer */);
     ERTS_REQ_PROC_MAIN_LOCK(c_p);
     SWAPIN;
     E += 3;
@@ -135,10 +135,10 @@ i_perf_counter() {
 
     ts = erts_sys_perf_counter();
     if (IS_SSMALL(ts)) {
-        r(0) = make_small((Sint)ts);
+        x(0) = make_small((Sint)ts);
     } else {
         $GC_TEST(0, ERTS_SINT64_HEAP_SIZE(ts), 0);
-        r(0) = make_big(HTOP);
+        x(0) = make_big(HTOP);
 #if defined(ARCH_32)
         if (ts >= (((Uint64) 1) << 32)) {
             *HTOP = make_pos_bignum_header(2);
diff --git a/erts/emulator/utils/beam_makeops b/erts/emulator/utils/beam_makeops
index 796fff7182..a3d18bfbe0 100755
--- a/erts/emulator/utils/beam_makeops
+++ b/erts/emulator/utils/beam_makeops
@@ -1728,7 +1728,7 @@ sub code_gen {
                 last SWITCH;
             };
 	    /r/ and do {
-                push(@f, "r(0)");
+                push(@f, "x(0)");
                 last SWITCH;
             };
 	    /[lxyS]/ and do {
-- 
2.35.3

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File 3851-emulator-Remove-vestiges-of-special-handling-of-x-0.patch of Package erlang (Revision 54461a2357af3de1f765489d2fd0ee14)

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