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Re: Power4 should treat mftb as extended mfspr mnemonic

On Sun, Nov 30, 2014 at 12:02:09PM -0600, Segher Boessenkool wrote:
> On Sun, Nov 30, 2014 at 01:36:55PM +1030, Alan Modra wrote:
> > On Fri, Nov 28, 2014 at 02:34:54PM +1030, Alan Modra wrote:
> > > mftb is marked phased out in the architecture manual, but we can keep
> > > it as an extended mnemonic for mftbl.
> > 
> > On further reading of ISA manual it appears gas should have been
> > treating mftb and mftbu as extended mnemonics for mfspr, for ISA 2.03
> > and later.  The 31,371 opcode is phased out, not the mnemonic.
> > 
> > opcodes/
> > 	* ppc-opc.c (powerpc_opcodes): Make mftb* generate mfspr for
> > 	power4 and later.
> Does that work with current GCC (for its mftb builtins)?  I.e. what
> does this do with -many, does it generate mftb or mfspr insns?

It depends on what cpu option is passed to gas before -many.  So for
instance -mpower7 -many will get you mfspr, -mppc64 -many will give
you mftb.

> > - 4b4:	(7c 6c 42 e6|e6 42 6c 7c) 	mftbl   r3
> > + 4b4:	(7c 6c 42 a6|a6 42 6c 7c) 	mftb    r3
> Nice to see this nuisance finally fixed.  Although, only for 476 and a2?

No, like the changelog says, for power4 and later.  We lack testsuite

grep mftb *.s
476.s:	mftb	3
a2.s:	mftb	10,268
a2.s:	mftb	10,269
titan.s:	mftbl		4
titan.s:	mftb		4
titan.s:	mftbu		4

Alan Modra
Australia Development Lab, IBM

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