On Tuesday 17 August 2010 16:15:40 you wrote:
> Job Noorman <jobnoorman@xxxxxxxxx> writes:
> > Consider the following code snippet:
> > struct Foo
> > {
> >
> > void foobar() {}
> >
> > };
> >
> > typedef void (*plain_foobar_t)(Foo*);
> >
> > void test()
> > {
> >
> > asm("push %0;"
> >
> > : "i"((plain_foobar_t)&Foo::foobar));
> >
> > }
> >
> > int main(){}
> >
> > If I compile this with
> >
> > g++ -Wno-pmf-conversions main.cpp
> >
> > I get the following;
> >
> > main.cpp: In function ‘void test()’:
> > main.cpp:12: warning: asm operand 0 probably doesn’t match
> > constraints main.cpp:12: error: impossible constraint in ‘asm’
>
> I would not expect this kind of thing to work when not optimizing. You
> are requiring the compiler to see that the value is an integer constant,
> which the compiler can't reliably do when not optimizing.
>
> It should work reliably with or without optimization if you use an "r"
> constraint, though of course that will introduce an additional
> instruction.
>
> Ian
When I use the "r" constraint, it indeed works and GCC emits the following
code:
movl $_ZN3Foo6foobarEv, %eax
push %eax;
What I find strange about this is that GCC has converted
"(plain_foobar_t)&Foo::foobar" in a constant value ($_ZN3Foo6foobarEv) without
using optimizations. So why can't it do the same when using the "i"
constraint?
Job
