1
0
Fork 0
mirror of https://github.com/ruby/ruby.git synced 2022-11-09 12:17:21 -05:00
ruby--ruby/include
naruse ac6f08df23 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
2017-03-07 03:35:47 +00:00
..
ruby Use ADD instead of MUL 2017-03-07 03:35:47 +00:00
ruby.h