From ac6f08df231d6f4972de75461a2a835c54fe1270 Mon Sep 17 00:00:00 2001
From: naruse <naruse@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Tue, 7 Mar 2017 03:35:47 +0000
Subject: Use ADD instead of MUL

* On recent CPUs, 2-operand MUL's latency is 3 cycle but ADD is 1 cycle.
* clang Optimizes `MUL rax,2` into `ADD rax,rax` but gcc7 doesn't.
* LONG2FIX is compiled into `lea r14,[r15+r15*1+0x1]`; this is 1cycle
  and run in parallel if the branch prediction is correct.
* Note that old (RB_POSFIXABLE(f) && RB_NEGFIXABLE(f)) is usually uses
  following instructions.
  * movabs rax,0x4000000000000000
  * add    rax,rdi
  * js
  It needs large immediate and Macro-Fusion is not applied.
  ADD and JO is much smaller though it is also Macro-Fusion unfriendly.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57793 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
---
 bignum.c            | 10 ----------
 include/ruby/ruby.h | 17 +++++------------
 2 files changed, 5 insertions(+), 22 deletions(-)

diff --git a/bignum.c b/bignum.c
index 50700b4c4a..0e15e58c12 100644
--- a/bignum.c
+++ b/bignum.c
@@ -4436,18 +4436,8 @@ rb_ull2inum(unsigned LONG_LONG n)
 VALUE
 rb_ll2inum(LONG_LONG n)
 {
-#ifdef HAVE_BUILTIN___BUILTIN_MUL_OVERFLOW
-    SIGNED_VALUE v;
-    if (__builtin_mul_overflow(n, 2, &v)) {
-	return rb_ll2big(n);
-    }
-    else {
-	return ((VALUE)v) | RUBY_FIXNUM_FLAG;
-    }
-#else
     if (FIXABLE(n)) return LONG2FIX(n);
     return rb_ll2big(n);
-#endif
 }
 
 #endif  /* HAVE_LONG_LONG */
diff --git a/include/ruby/ruby.h b/include/ruby/ruby.h
index 0cd88fb002..1cc9937acb 100644
--- a/include/ruby/ruby.h
+++ b/include/ruby/ruby.h
@@ -359,7 +359,11 @@ rb_fix2ulong(VALUE x)
 #define RB_FIXNUM_P(f) (((int)(SIGNED_VALUE)(f))&RUBY_FIXNUM_FLAG)
 #define RB_POSFIXABLE(f) ((f) < RUBY_FIXNUM_MAX+1)
 #define RB_NEGFIXABLE(f) ((f) >= RUBY_FIXNUM_MIN)
-#define RB_FIXABLE(f) (RB_POSFIXABLE(f) && RB_NEGFIXABLE(f))
+#if defined HAVE_BUILTIN___BUILTIN_ADD_OVERFLOW
+# define RB_FIXABLE(f) ({SIGNED_VALUE a=(f),c; !__builtin_add_overflow(a, a, &c);})
+#else
+# define RB_FIXABLE(f) (RB_POSFIXABLE(f) && RB_NEGFIXABLE(f))
+#endif
 #define FIX2LONG(x) RB_FIX2LONG(x)
 #define FIX2ULONG(x) RB_FIX2ULONG(x)
 #define FIXNUM_P(f) RB_FIXNUM_P(f)
@@ -1507,16 +1511,6 @@ rb_integer_type_p(VALUE obj)
 static inline int
 rb_long2fix_overflow(long l, VALUE *ptr)
 {
-#ifdef HAVE_BUILTIN___BUILTIN_MUL_OVERFLOW
-    SIGNED_VALUE v;
-    if (__builtin_mul_overflow(l, 2, &v)) {
-	return 1;
-    }
-    else {
-	*ptr = ((VALUE)v) | RUBY_FIXNUM_FLAG;
-	return 0;
-    }
-#else
     if (RB_FIXABLE(l)) {
 	*ptr = RB_LONG2FIX(l);
 	return 0;
@@ -1524,7 +1518,6 @@ rb_long2fix_overflow(long l, VALUE *ptr)
     else {
 	return 1;
     }
-#endif
 }
 
 #if SIZEOF_INT < SIZEOF_LONG
-- 
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