Stop trying to maximize the use of x(0)

X register 0 used to be mapped to a hardware register, and therefore
faster than the other registers. Because of that, the compiler
tried to use x(0) as much as possible as a temporary register.

That was changed a few releases ago. X register 0 is now placed
in the array of all X registers and has no special speed
advantage compared to the other registers.

Remove the code in the compiler that attempts to use x(0) as
much as possible. As a result, the following type of instruction
will be much less frequent:

 {put_list,Src,{x,0},{x,0}}

Instead, the following type of instruction will be more frequent:

 {put_list,Src,{x,X},{x,X}}

(Where X is an arbitrary X register.)

Update the runtime system to specialize that kind of put_list
instruction.

1 files changed, 7 insertions, 0 deletions

diff --git a/erts/emulator/beam/instrs.tab b/erts/emulator/beam/instrs.tab
index c17d1a8f69..d934abb217 100644
--- a/erts/emulator/beam/instrs.tab
+++ b/erts/emulator/beam/instrs.tab
@@ -542,6 +542,13 @@ put_list(Hd, Tl, Dst) {
     HTOP += 2;
 }
 
+update_list(Hd, Dst) {
+    HTOP[0] = $Hd;
+    HTOP[1] = $Dst;
+    $Dst = make_list(HTOP);
+    HTOP += 2;
+}
+
 i_put_tuple := i_put_tuple.make.fill;
 
 i_put_tuple.make(Dst) {