Ruby

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