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authornaruse <naruse@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>2017-03-07 03:35:47 +0000
committernaruse <naruse@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>2017-03-07 03:35:47 +0000
commitac6f08df231d6f4972de75461a2a835c54fe1270 (patch)
tree0444aa77572bfb96a5b17e172486a8f8580eef0c /ext/readline
parentd4c598c441ef408fbab3db544d30525b5bc9c1e9 (diff)
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
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