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

1 files changed, 0 insertions, 10 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 */