Make the swap instruction known to the compiler

BEAM has had a `swap` instruction for several releases, but it was not
known to the compiler. The loader would translate a sequence of three
`move` instructions to the `swap` instructions, but only when it was
possible to determine that it would be safe.

By making `swap` known to the compiler, it can be applied in more
situations since it is easier for the compiler than for the loader
to ensure that the usage is safe, and the loader shenanigans can be
eliminated.

3 files changed, 9 insertions, 100 deletions

diff --git a/erts/emulator/beam/beam_load.c b/erts/emulator/beam/beam_load.c
index 941c3ebbbe..0de694f449 100644
--- a/erts/emulator/beam/beam_load.c
+++ b/erts/emulator/beam/beam_load.c
@@ -3131,27 +3131,6 @@ mixed_types(LoaderState* stp, GenOpArg Size, GenOpArg* Rest)
     return 0;
 }
 
-static int
-is_killed_apply(LoaderState* stp, GenOpArg Reg, GenOpArg Live)
-{
-    return Reg.type == TAG_x && Live.type == TAG_u &&
-	Live.val+2 <= Reg.val;
-}
-
-static int
-is_killed(LoaderState* stp, GenOpArg Reg, GenOpArg Live)
-{
-    return Reg.type == TAG_x && Live.type == TAG_u &&
-	Live.val <= Reg.val;
-}
-
-static int
-is_killed_by_call_fun(LoaderState* stp, GenOpArg Reg, GenOpArg Live)
-{
-    return Reg.type == TAG_x && Live.type == TAG_u &&
-	Live.val+1 <= Reg.val;
-}
-
 /*
  * Test whether register Reg is killed by make_fun instruction that
  * creates the fun given by index idx.
@@ -3172,16 +3151,6 @@ is_killed_by_make_fun(LoaderState* stp, GenOpArg Reg, GenOpArg idx)
 }
 
 /*
- * Test whether register Reg is killed by the send instruction that follows.
- */
-
-static int
-is_killed_by_send(LoaderState* stp, GenOpArg Reg)
-{
-    return Reg.type == TAG_x && 2 <= Reg.val;
-}
-
-/*
  * Generate an instruction for element/2.
  */
 
diff --git a/erts/emulator/beam/instrs.tab b/erts/emulator/beam/instrs.tab
index 462ee77e6f..c77e5eae58 100644
--- a/erts/emulator/beam/instrs.tab
+++ b/erts/emulator/beam/instrs.tab
@@ -683,10 +683,11 @@ swap(R1, R2) {
     $R2 = V;
 }
 
-swap_temp(R1, R2, Tmp) {
-    Eterm V = $R1;
-    $R1 = $R2;
-    $R2 = $Tmp = V;
+swap2(R1, R2, R3) {
+    Eterm V = $R2;
+    $R2 = $R1;
+    $R1 = $R3;
+    $R3 = V;
 }
 
 test_heap(Nh, Live) {
diff --git a/erts/emulator/beam/ops.tab b/erts/emulator/beam/ops.tab
index 10ca74cd60..1beeb67c1f 100644
--- a/erts/emulator/beam/ops.tab
+++ b/erts/emulator/beam/ops.tab
@@ -324,76 +324,15 @@ move_src_window2 y x x
 move_src_window3 y x x x
 move_src_window4 y x x x x
 
-# Swap registers.
-move R1=xy Tmp=x | move R2=xy R1 | move Tmp R2 => swap_temp R1 R2 Tmp
-
-# The compiler uses x(1022) when swapping registers. It will definitely
-# not be used again.
-swap_temp R1 R2 Tmp=x==1022 => swap R1 R2
-
-swap_temp R1 R2 Tmp | move Src Tmp => swap R1 R2 | move Src Tmp
-
-swap_temp R1 R2 Tmp | line Loc | apply Live | is_killed_apply(Tmp, Live) => \
-  swap R1 R2 | line Loc | apply Live
-swap_temp R1 R2 Tmp | line Loc | apply_last Live D | is_killed_apply(Tmp, Live) => \
-  swap R1 R2 | line Loc | apply_last Live D
-
-swap_temp R1 R2 Tmp | line Loc | call_fun Live | is_killed_by_call_fun(Tmp, Live) => \
-  swap R1 R2 | line Loc | call_fun Live
-swap_temp R1 R2 Tmp | make_fun2 OldIndex=u | is_killed_by_make_fun(Tmp, OldIndex) => \
-  swap R1 R2 | make_fun2 OldIndex
-
-swap_temp R1 R2 Tmp | line Loc | call Live Addr | is_killed(Tmp, Live) => \
-  swap R1 R2 | line Loc | call Live Addr
-swap_temp R1 R2 Tmp | call_only Live Addr | \
-  is_killed(Tmp, Live) => swap R1 R2 | call_only Live Addr
-swap_temp R1 R2 Tmp | call_last Live Addr D | \
-  is_killed(Tmp, Live) => swap R1 R2 | call_last Live Addr D
-
-swap_temp R1 R2 Tmp | line Loc | call_ext Live Addr | is_killed(Tmp, Live) => \
-  swap R1 R2 | line Loc | call_ext Live Addr
-swap_temp R1 R2 Tmp | line Loc | call_ext_only Live Addr | \
-  is_killed(Tmp, Live) => swap R1 R2 | line Loc | call_ext_only Live Addr
-swap_temp R1 R2 Tmp | line Loc | call_ext_last Live Addr D | \
-  is_killed(Tmp, Live) => swap R1 R2 | line Loc | call_ext_last Live Addr D
-
-swap_temp R1 R2 Tmp | call_ext Live Addr | is_killed(Tmp, Live) => \
-  swap R1 R2 | call_ext Live Addr
-swap_temp R1 R2 Tmp | call_ext_only Live Addr | is_killed(Tmp, Live) => \
-  swap R1 R2 | call_ext_only Live Addr
-swap_temp R1 R2 Tmp | call_ext_last Live Addr D | is_killed(Tmp, Live) => \
-  swap R1 R2 | call_ext_last Live Addr D
-
-swap_temp R1 R2 Tmp | move Src Any | line Loc | call Live Addr | \
-  is_killed(Tmp, Live) | distinct(Tmp, Src) => \
-     swap R1 R2 | move Src Any | line Loc | call Live Addr
-swap_temp R1 R2 Tmp | move Src Any | line Loc | call_ext Live Addr | \
-  is_killed(Tmp, Live) | distinct(Tmp, Src) => \
-     swap R1 R2 | move Src Any | line Loc | call_ext Live Addr
-swap_temp R1 R2 Tmp | move Src Any | call_only Live Addr | \
-  is_killed(Tmp, Live) | distinct(Tmp, Src) => \
-    swap R1 R2 | move Src Any | call_only Live Addr
-swap_temp R1 R2 Tmp | move Src Any | line Loc | call_ext_only Live Addr | \
-  is_killed(Tmp, Live) | distinct(Tmp, Src) => \
-    swap R1 R2 | move Src Any | line Loc | call_ext_only Live Addr
-swap_temp R1 R2 Tmp | move Src Any | line Loc | call_fun Live | \
-  is_killed(Tmp, Live) | distinct(Tmp, Src) => \
-    swap R1 R2 | move Src Any | line Loc | call_fun Live
-
-swap_temp R1 R2 Tmp | line Loc | send | is_killed_by_send(Tmp) => \
-  swap R1 R2 | line Loc | send
-
-# swap_temp/3 with Y register operands are rare.
-swap_temp R1 R2=y Tmp => swap R1 R2 | move R2 Tmp
-swap_temp R1=y R2 Tmp => swap R1 R2 | move R2 Tmp
-
 swap R1=x R2=y => swap R2 R1
 
-swap_temp x x x
-
 swap xy x
 swap y y
 
+swap R1=x R2=x | swap R3=x R1 => swap2 R1 R2 R3
+
+swap2 x x x
+
 # move_shift
 
 move SD=x    D=x | move Src=cxy SD=x  | distinct(D, Src) => move_shift Src SD D