Re: PPC questions

[Ian Lance Taylor <iant at google dot com>]

"Jan Beulich" <jbeulich@novell.com> writes:

> Two (technically unrelated, but they came up in the same context) questions:
>
> 1) The recent Power7 commit adds support for new instructions utilizing
> new registers. While the disassembler shows them as vs{0-63}, using
> register names in the assembler isn't possible (i.e. one has to use plain
> numbers). Is this simply an oversight, for which a patch would be accepted,
> or is there a reason? (Btw., I always found it quite confusing that the
> assembler doesn't really care what register kind gets used with instructions,
> as they are all just getting converted to numbers, but I assume that has
> some [perhaps historical] reason.)

When I first wrote the PowerPC assembler port, it only accepted
numbers, because that was how the AIX assembler behaved.  If you
wanted names you needed to use .S files and #define (the header file
with the #define's is gcc/config/rs6000/ppc-asm.h).  Somebody later
added the ability to use register names, along with the -mregnames and
-mno-regnames options.

I don't know anything about the Power7 patch, but I assume it was an
oversight that the new register names were not listed in the
pre_defined_registers table.


> 2) While the assembler (by default) requires % to precede register names,
> the disassembler doesn't produce similar output - there's not even a switch
> to make it do. Is that intentional?

That is also historical.  I think that my original code just printed
numbers, but people rebelled (those darn users).  When people used
#define with the assembler, naturally no % was required.  So the
disassembler is essentially printing the kind of assembler code you
might write after a #include of ppc-asm.h.

Ian