Re: [PATCH, GCC/ARM/gcc-7-branch] Backport PR71607

[Prakhar Bahuguna <prakhar.bahuguna@arm.com>]

On 31/05/2017 14:11:43, Richard Sandiford wrote:
> Prakhar Bahuguna <prakhar.bahuguna@arm.com> writes:
> > On 31/05/2017 09:19:40, Richard Sandiford wrote:
> >> const_ints are supposed to be stored in sign-extended form, so a 32-bit
> >> integer with the MSB set should be 0xffffffff80000000|x instead of
> >> 0x80000000|x.  It's a bug if you have one where that isn't true.
> >> 
> >> In the patch it looks like this could come from:
> >> ...these two splits, where the GEN_INTs should probably be:
> >> 
> >>   gen_int_mode (..., SImode);
> >> 
> >> instead.
> >
> > Hi Richard, thanks for the tip. Is there a test case that could produce an
> > incorrect result? I've attempted to create one using negative doubles and
> > floats but haven't succeeded.
> 
> Just to check, are you testing with --enable-checking=yes,rtl?
> 
> When the values you tried were split, did you get the sign-extended form
> or the zero-extended form?
> 
> Thanks,
> Richard

I've now rebuilt with --enable-checking=yes,rtl and it appears that the split
values are being correctly sign-extended in the rtl and appear correctly in the
assembly.

However, if you believe it is safer to use gen_int_mode(), I'll respin the
patch accordingly.

-- 

Prakhar Bahuguna