[cfe-commits] [patch][commit-after-review] asm comma-separated clobberlists

[Eli Friedman]

On Wed, Aug 12, 2009 at 9:51 AM, Ryan Flynn<parseerror at gmail.com> wrote:
> patch to handle commas in clobberlists like gcc does. i.e. "=A,A"
>
> the form "=AA" already appears to work, but the commas were causing
> trouble in semantic validation ("," unrecognized) and in parsing
> canonicalized asm (which already uses "," to separate constraints)
>
> error found in FreeBSD driver, but examples found elsewhere for 32-bit
> targets handling 64-bit math, i.e.
> http://gcc.gnu.org/ml/gcc-bugs/2000-02/msg00104.html (search for
> "=A,A")
>
> passes all clang tests; i wanted a review because my asm-fu is weak.
> let me know if this is horrible. thanks!

This patch simply isn't correct.  Take something like the following on x86:

int x,y;
void a() {
asm("add %0,%1" : "+r,m"(x) : "rm,r"(y));
}

With this patch, if I'm not mistaken, both operands will end up in
memory, which is illegal.

If you haven't seen them, docs are at
http://gcc.gnu.org/onlinedocs/gcc/Multi_002dAlternative.html .

-Eli