Re: Visual C++ style inline asms

[Richard Henderson <rth at redhat dot com>]

On Tue, Jun 14, 2005 at 09:26:11PM -0400, Andrew Pinski wrote:
> On Jun 14, 2005, at 9:25 PM, Mike Stump wrote:
> >Any objections to adding Visual C++ style inline asms?
> 
> Didn't RTH objected the last time?

One has to do a less gross job of it than Red Hat did.  I suppose
I could be prodded into pulling out the code so that you can see
where the bar is.

You'll need and EXTREMELY large testsuite.  You'll find that the MS
documentation is useless, and you'll have to deduce the desired
semantics from customer code bases.  Presumably Apple can find 
large customers who will want this kind of thing and can arrange
to code exchanges in some way, if only NDA.  But if NDA, I expect
reduced test cases to make their way into our testsuite.

Expect to want to implement "naked" functions as well, because MS
does, and quite a lot of VC++ inline asm code expects to use them.
Expect me to barf on your shoes.

I don't recall if Darwin uses %ebx for pic code like ELF.  If you
do, expect to find that lots of user code expects to be able to
clobber it, because Windows doesn't do pic code at all, and so
reserves no such register.

I suspect that one could get quite a lot of milage out of parsing
the assembly code and turning most of it into straight GIMPLE, rather
than into ASM_EXPRs.  A great many examples of VC++ inline asms that
I've seen were completely and utterly trivial; the compiler could have
done a better job.  Of course there will be cases that you either
can't understand, or use instructions that don't map to an EXPR or a
builtin.  But I expect that more often than not, you can reduce the
inline asm block to one such insn, and expose all the rest of the
data movement to the compiler.



r~