On Wed, 20 Jan 2021, Jakub Jelinek wrote:
> On Wed, Jan 20, 2021 at 01:15:12PM +0100, Richard Biener wrote:
> > OK, fixed. Guess we could also use __builtin_mul_overflow directly
> > if supported via a GCC_VERSION check. Looks like it's present
> > since GCC 5 at least. So sth like (incremental)
> >
> > diff --git a/gcc/hwint.h b/gcc/hwint.h
> > index 53f4ed5dcad..6d2d491acfa 100644
> > --- a/gcc/hwint.h
> > +++ b/gcc/hwint.h
> > @@ -354,12 +354,19 @@ add_hwi (HOST_WIDE_INT a, HOST_WIDE_INT b, bool
> > *overflow)
> > inline HOST_WIDE_INT
> > mul_hwi (HOST_WIDE_INT a, HOST_WIDE_INT b, bool *overflow)
> > {
> > +#if GCC_VERSION < 5001
> > unsigned HOST_WIDE_INT result = a * (unsigned HOST_WIDE_INT)b;
> > - if (a != 0 && (HOST_WIDE_INT)result / a != b)
> > + if ((a == -1 && b == HOST_WIDE_INT_MIN)
> > + || (a != 0 && (HOST_WIDE_INT)result / a != b))
> > *overflow = true;
> > else
> > *overflow = false;
> > return result;
> > +#else
> > + HOST_WIDE_INT result;
> > + *overflow = __builtin_mul_overflow (a, b, &result);
> > + return result;
> > +#endif
> > }
> >
> > for the add case we should match all of the function I guess.
>
> Yeah, sure.
> Maybe bump somewhat the GCC_VERSION number in there, we've had bugs in
> __builtin_mul_overflow expansion too.
Wow, a bugzilla search finds wrong-code that's only fixed in 9.3+.
So I guess I'll check for GCC 11+ then and not worry for stage1,
non-bootstrapped GCC or crosses with host != GCC 11.
Richard.
