MS/CW-style inline assembly for GCC

[Andrew Pinski]

On May 3, 2004, at 18:16, Stan Shebs wrote:

> However, the syntax has also been somewhat inaccessible. Those
> constraint letters were often undocumented, and are still somewhat
> mysterious to users, while the use of strings for instructions makes
> the construction of longer assembly sequences a rather difficult
> undertaking. In addition, the "capture" of GCC's constraint letters
> and pattern syntax into source code has the potential to reduce our
> flexibility to change compiler internals later.

If the constraint letters are undocumented either they should be removed
or documented.  Or really documented better as they are documented 
weakly
now.

Now on the other hand operand operators are not documented but most 
people
do not use them and should not be used at all.

I have the view now that any use of inline-asm is usually wrong except 
when
the instruction is not avialable to compiler to use such as mftbu/mftb 
and
instructions which implement atomic operations (but then again there is
already a request for builtins for the atomic operations, PR 14311).
And there could be target dependent builtins for most other things such 
as
mftbu/mftb.

And if the people wants to program in asm, they should not be using a
compiler to do the work.

And then only the few will need ever inline-asm. In fact for IA64, 
inline-asm
is discerned as getting the instruction packet just right is very prone 
to bugs.

Also the MS/CW style of inline-asm will cause more problems as how 
would you know
what registers to mark as clobber and if the memory is clobbered?  Do 
you mark them
all as clobbered except for a select few or do you need to parse the 
asm too which
in that case we really need to start thinking about integrating gas 
into GCC
like any commercial compiler already does.  I think this is best 
approach any ways
except that some targets are not yet supported by fully gas (like 
Darwin and IIRC AIX).

Thanks,
Andrew Pinski