On Sat, Aug 05, 2017 at 01:56:49PM +0200, Thomas Petazzoni wrote:
> On Sat, 5 Aug 2017 00:25:00 +0200, Ralf Baechle wrote:
>
> > > Great! However, looking at the functions that end up calling __multi3,
> > > I'm wondering why suddenly gcc 7.x needs to call such a function, while
> > > the same code was compiling without __multi3 in libgcc with gcc 6.x.
> >
> > Chances are it's something specific to MIPS64 R6. Before trying your
> > config file I also tried a number of other defconfigs and all built
> > well.
> >
> > Here's a test case which generates a reference to __multi3:
> >
> > unsigned long func(unsigned long a, unsigned long b)
> > {
> > return a > (~0UL) / b;
> > }
> >
> > GCC rearanges above statement to:
> >
> > return (unsigned __int128)a * (unsigned __int128) b > 0xffffffff;
>
> And this is normal/expected ?
Without consideration of performance, It's certainly is valid code. And
with that I can't drop the issue as a GCC code generation bug.
However it seems GCC itself doesn't seem to have a __multi3 in its
libgcc2 - which indeed would be a GCC issue - at least none I was easily
able to find with grep so I'm adding Matthew Fortune to cc in the hope he
can shed some light on this.
Ralf
