[cfe-dev] MRV on x86_64

[Arushi Aggarwal]

On Thu, Mar 10, 2011 at 3:40 PM, Eli Friedman <eli.friedman at gmail.com>wrote:

> On Thu, Mar 10, 2011 at 1:09 PM, Arushi Aggarwal <arushi987 at gmail.com>
> wrote:
> > Hi,
> >
> > I am using clang on the following code,
> >
> > struct S {
> >   float a,b,c;
> > };
> >
> > void foo(struct S obj) {
> >   obj.a = 1.2;
> > }
> >
> > int main() {
> >   struct S s;
> >   s.a = 1.0;
> >   s.b = 1.0;
> >   s.c = 1.0;
> >   foo(s);
> >   return 0;
> > }
> >
> > The generated code for foo, changes the type of the argument to foo to be
> > {double, double} .
> >
> > llvm-gcc was converting this to {double, float} which was an ABI
> > requirement, as par an older
> > discussion(
> http://lists.cs.uiuc.edu/pipermail/llvmdev/2010-January/028870.html)
> >
> > Why does clang change it to a struct with a different size?
>
> clang uses different code written from scratch, so there are
> differences in the output.  In this case, it's a missed optimization;
> ideally, I think the signature of foo would be @_Z3foo1S(<2 x float>,
> float).
>

Is this something that I should maybe file a bug for?

Thanks!
Arushi

>
> -Eli
>
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