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.

2 files changed, 12 insertions, 2 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) {
diff --git a/erts/emulator/beam/ops.tab b/erts/emulator/beam/ops.tab
index 3df91056cb..c30af029ce 100644
--- a/erts/emulator/beam/ops.tab
+++ b/erts/emulator/beam/ops.tab
@@ -503,6 +503,10 @@ i_put_tuple xy I
 #
 put_list Const=c n Dst => move Const x | put_list x n Dst
 
+put_list Src Dst=x Dst => update_list Src Dst
+
+update_list xyc x
+
 put_list x n x
 put_list y n x
 put_list x x x
@@ -525,8 +529,6 @@ put_list c y x
 
 # The following put_list instructions using x(0) are frequently used.
 
-put_list y r r
-put_list x r r
 put_list r n r
 put_list r n x
 put_list r x x
@@ -537,6 +539,7 @@ put_list x x r
 put_list s s d
 %hot
 
+
 #
 # Some more only used by the emulator
 #