On Fri, 19 May 2017, Alexander Monakov wrote:
> On Fri, 19 May 2017, Joseph Myers wrote:
> > On Fri, 19 May 2017, Alexander Monakov wrote:
> > > (to be precise, if the multiplication is done in a signed type and the
> > > middle
> > > constant factor was a negated power of two, the sign change ne
On Fri, 19 May 2017, Joseph Myers wrote:
> On Fri, 19 May 2017, Alexander Monakov wrote:
> > (to be precise, if the multiplication is done in a signed type and the
> > middle
> > constant factor was a negated power of two, the sign change needs to remain:
> >
> > a * -4 * b * 2
> >
> > needs
On Fri, 19 May 2017, Alexander Monakov wrote:
> On Fri, 19 May 2017, Marek Polacek wrote:
> > > I think it's possible to keep this folding, note that it's valid to
> > > transform to
> > >
> > > (n * 1 * z) * 50
> > >
> > > (i.e. accumulate multiplications on the outermost factor)
>
>
On May 19, 2017 5:47:10 PM GMT+02:00, Alexander Monakov
wrote:
>On Fri, 19 May 2017, Marek Polacek wrote:
>> > I think it's possible to keep this folding, note that it's valid to
>transform to
>> >
>> > (n * 1 * z) * 50
>> >
>> > (i.e. accumulate multiplications on the outermost factor)
On Fri, 19 May 2017, Marek Polacek wrote:
> > I think it's possible to keep this folding, note that it's valid to
> > transform to
> >
> > (n * 1 * z) * 50
> >
> > (i.e. accumulate multiplications on the outermost factor)
(to be precise, if the multiplication is done in a signed type an
On Fri, May 19, 2017 at 01:57:24PM +0300, Alexander Monakov wrote:
> On Fri, 19 May 2017, Richard Biener wrote:
>
> > On Fri, 19 May 2017, Marek Polacek wrote:
> >
> > > On Fri, May 19, 2017 at 09:58:45AM +0200, Richard Biener wrote:
> > > > On Fri, 19 May 2017, Marek Polacek wrote:
> > > >
> >
On Fri, 19 May 2017, Richard Biener wrote:
> On Fri, 19 May 2017, Marek Polacek wrote:
>
> > On Fri, May 19, 2017 at 09:58:45AM +0200, Richard Biener wrote:
> > > On Fri, 19 May 2017, Marek Polacek wrote:
> > >
> > > > extract_muldiv folds
> > > >
> > > > (n * 1 * z) * 50
> > > >
> > >
On Fri, 19 May 2017, Marek Polacek wrote:
> On Fri, May 19, 2017 at 09:58:45AM +0200, Richard Biener wrote:
> > On Fri, 19 May 2017, Marek Polacek wrote:
> >
> > > extract_muldiv folds
> > >
> > > (n * 1 * z) * 50
> > >
> > > to
> > >
> > > (n * 50) * z
> > >
> > > which is a wro
On Fri, May 19, 2017 at 09:58:45AM +0200, Richard Biener wrote:
> On Fri, 19 May 2017, Marek Polacek wrote:
>
> > extract_muldiv folds
> >
> > (n * 1 * z) * 50
> >
> > to
> >
> > (n * 50) * z
> >
> > which is a wrong transformation to do, because it may introduce an overflow.
> >
On Fri, 19 May 2017, Marek Polacek wrote:
> extract_muldiv folds
>
> (n * 1 * z) * 50
>
> to
>
> (n * 50) * z
>
> which is a wrong transformation to do, because it may introduce an overflow.
> This resulted in a ubsan false positive. So we should just disable this
> folding altog
extract_muldiv folds
(n * 1 * z) * 50
to
(n * 50) * z
which is a wrong transformation to do, because it may introduce an overflow.
This resulted in a ubsan false positive. So we should just disable this
folding altogether. Does the approach I took make sense?
Bootstrapped/regtes
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