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Re: MIPS assembler branch relaxations


On Sep 14, 2002, Thiemo Seufer <ica2_ts@csv.ica.uni-stuttgart.de> wrote:

>> Why beqzl?  Admittedly, I don't know much about MIPS hardware, but I'd
>> think that just "b" would probably be faster, since that's the normal
>> unconditional branch.

> "b" isn't a valid opcode. :-)

Right.  `b foo' is just a shorthand for `beq $0, $0, foo'

> Btw, "beqzl" also isn't one.

Huh?  Please check your ISA manual again.  It surely is there.

> In this special case I'd prefer "beq".

Then other branch prediction forms would kick in, and the branch would
probably be considered unlikely for being a forward branch.  I don't
know whether mips has any such considerations, but indicating the
branch is likely if there is a way to do so is an obvious improvement
to me.

-- 
Alexandre Oliva   Enjoy Guarana', see http://www.ic.unicamp.br/~oliva/
Red Hat GCC Developer                 aoliva@{redhat.com, gcc.gnu.org}
CS PhD student at IC-Unicamp        oliva@{lsd.ic.unicamp.br, gnu.org}
Free Software Evangelist                Professional serial bug killer


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