* insns.def (opt_plus): use `- 1` instead of `& (~1)` to allow

  compilers to use x86 LEA instruction (3 operand).
  Even if 3 operand LEA's latency is 3 cycle after SandyBridge,
  it reduces code size and can be faster because of super scalar.

* insns.def (opt_plus): calculate and use rb_int2big.
  On positive Fixnum overflow, `recv - 1 + obj` doesn't carry
  because recv's msb and obj's msb are 0, and resulted msb is 1.
  Therefore simply rshift and cast as signed long works fine.
  On negative Fixnum overflow, it will carry because both arguments'
  msb are 1, and resulted msb is also 1.
  In this case it needs to restore carried sign bit after rshift.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@55515 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 15 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index cd43b4a272..6be1c45802 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,18 @@
+Tue Jun 28 02:41:32 2016  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* insns.def (opt_plus): use `- 1` instead of `& (~1)` to allow
+	  compilers to use x86 LEA instruction (3 operand).
+	  Even if 3 operand LEA's latency is 3 cycle after SandyBridge,
+	  it reduces code size and can be faster because of super scalar.
+
+	* insns.def (opt_plus): calculate and use rb_int2big.
+	  On positive Fixnum overflow, `recv - 1 + obj` doesn't carry
+	  because recv's msb and obj's msb are 0, and resulted msb is 1.
+	  Therefore simply rshift and cast as signed long works fine.
+	  On negative Fixnum overflow, it will carry because both arguments'
+	  msb are 1, and resulted msb is also 1.
+	  In this case it needs to restore carried sign bit after rshift.
+
 Mon Jun 27 16:58:32 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* lib/fileutils.rb (FileUtils#install): accecpt symbolic mode, as