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Re: [PATCH, GCC/ARM/gcc-7-branch] Backport PR71607
- From: Richard Sandiford <richard dot sandiford at linaro dot org>
- To: Prakhar Bahuguna <prakhar dot bahuguna at arm dot com>
- Cc: <gcc-patches at gcc dot gnu dot org>, <nd at arm dot com>
- Date: Thu, 01 Jun 2017 07:15:47 +0100
- Subject: Re: [PATCH, GCC/ARM/gcc-7-branch] Backport PR71607
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Prakhar Bahuguna <email@example.com> writes:
> On 31/05/2017 14:11:43, Richard Sandiford wrote:
>> Prakhar Bahuguna <firstname.lastname@example.org> 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?
> 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
> However, if you believe it is safer to use gen_int_mode(), I'll respin the
> patch accordingly.
Yeah, I think it would be safer. But if they were already correctly
sign-extended, then what did you mean by:
Also the pattern for splitting 32-bit immediates had to be changed, it
was not accepting unsigned 32-bit unsigned integers with the MSB
set. I believe const_int_operand expects the mode of the operand to be
set to VOIDmode and not SImode. I have only changed it in the patterns
that were affecting this code, though I suggest looking into changing
it in the rest of the ARM backend.