https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90578
anlauf at gcc dot gnu.org changed:
What |Removed |Added
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CC| |anlauf at gcc dot gnu.org
--- Comment #4 from anlauf at gcc dot gnu.org ---
(In reply to rguent...@suse.de from comment #3)
> On Thu, 23 May 2019, dominiq at lps dot ens.fr wrote:
> > I don't see any mention of "left-shift by negative value is undefined".
>
> But it doesn't define what happens either ;) Thus it is "undefined" :P
>
> So, if the GNU extension would document it as "A LSHIFT by a
> negative value is treated as a RSHIFT" then the frontend has
> to emit y < 0 ? x >> y : x << y since what I am saying is that
> the middle-end follows the C standard here and treats negative
> shift amounts as undefined.
The gfortran documentation of LSHIFT (and RSHIFT) mentions:
"This function has been superseded by the ISHFT intrinsic, which is standard in
Fortran 95 and later."
The natural solution would be to implement LSHIFT/RSHIFT in terms of ISHFT,
which does handle positive and negative shifts.
I might have a look at it.
