From 4fe3f3b8be4825726fab6d4ea7515adf5b5df1ac Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Fri, 6 Oct 2017 08:52:32 +0200
Subject: Slightly speed up try/catch

The try_end and try_case instructions are implemented the same way
(try_case is translated to try_end by the loader).

We can do better than that. We know that try_case will only be executed
when an exception has been caught. Therefore, we know that x(0) is
the non-value and that x(1) through x(3) need to be shifted down to
x(0) through x(2). There is no need to test x(0) before shifting down.

try_end does not need the register shifting code at all.
---
 erts/emulator/beam/instrs.tab | 18 ++++++++++--------
 erts/emulator/beam/ops.tab    |  3 ++-
 2 files changed, 12 insertions(+), 9 deletions(-)

(limited to 'erts')

diff --git a/erts/emulator/beam/instrs.tab b/erts/emulator/beam/instrs.tab
index 07cc4bd527..20d356a81d 100644
--- a/erts/emulator/beam/instrs.tab
+++ b/erts/emulator/beam/instrs.tab
@@ -857,8 +857,7 @@ catch(Y, Fail) {
 }
 
 catch_end(Y) {
-    c_p->catches--;
-    make_blank($Y);
+    $try_end($Y);
     if (is_non_value(r(0))) {
         c_p->fvalue = NIL;
         if (x(1) == am_throw) {
@@ -888,12 +887,15 @@ catch_end(Y) {
 try_end(Y) {
     c_p->catches--;
     make_blank($Y);
-    if (is_non_value(r(0))) {
-        c_p->fvalue = NIL;
-        r(0) = x(1);
-        x(1) = x(2);
-        x(2) = x(3);
-    }
+}
+
+try_case(Y) {
+    $try_end($Y);
+    ASSERT(is_non_value(r(0)));
+    c_p->fvalue = NIL;
+    r(0) = x(1);
+    x(1) = x(2);
+    x(2) = x(3);
 }
 
 try_case_end(Src) {
diff --git a/erts/emulator/beam/ops.tab b/erts/emulator/beam/ops.tab
index 4a915c7762..7a2c39b3a8 100644
--- a/erts/emulator/beam/ops.tab
+++ b/erts/emulator/beam/ops.tab
@@ -188,7 +188,8 @@ catch_end y
 
 # Try/catch.
 try Y F => catch Y F
-try_case Y => try_end Y
+
+try_case y
 try_end y
 
 %cold
-- 
cgit v1.2.3