Introduce swap_temp/3 and swap/2

Sequences of three move instructionst that effectively swap the
contents of two registers are fairly common. We can replace them
with a swap_temp/3 instruction. The third operand is the temporary
register to be used for swapping, since the temporary register
may actually be used.

If swap_temp/3 instruction is followed by a call, the temporary
register will often (but not always) be killed by the call. If
it is killed, we can replace the swap_temp/3 instruction with a
slightly cheaper swap/2 instruction.

1 files changed, 14 insertions, 0 deletions

diff --git a/erts/emulator/beam/beam_emu.c b/erts/emulator/beam/beam_emu.c
index 2c10e7ae7c..4e6e7aa48a 100644
--- a/erts/emulator/beam/beam_emu.c
+++ b/erts/emulator/beam/beam_emu.c
@@ -545,6 +545,20 @@ void** beam_ops;
    HTOP += 2;                      \
   } while (0)
 
+#define Swap(R1, R2)				\
+  do {						\
+    Eterm V = R1;				\
+    R1 = R2;					\
+    R2 = V;					\
+  } while (0)
+
+#define SwapTemp(R1, R2, Tmp)			\
+  do {						\
+    Eterm V = R1;				\
+    R1 = R2;					\
+    R2 = Tmp = V;				\
+  } while (0)
+
 #define Move(Src, Dst, Store)      \
    do {                            \
        Eterm term = (Src);         \