On Fri, Mar 6, 2015 at 2:24 PM, Andi Kleen <[email protected]> wrote: > Denys Vlasenko <[email protected]> writes: > >> By the nature of TEST operation, it is often possible >> to test a narrower part of the operand: >> "testl $3, mem" -> "testb $3, mem", >> "testq $3, %rcx" -> "testb $3, %cl" >> This results in shorter insns, because TEST insn has no >> sign-entending byte-immediate forms unlike other ALU ops. > > It also results in expensive LCP stalls. Please don't do it. > If you feel the need to change instructions around like this read > the optimization manuals first.
Is this true for register access or just memory? --Andy > > -Andi > > -- > [email protected] -- Speaking for myself only -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
