This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Re: patch to fix constant math -5th patch, rtl
- From: Richard Sandiford <rdsandiford at googlemail dot com>
- To: Richard Biener <richard dot guenther at gmail dot com>
- Cc: Kenneth Zadeck <zadeck at naturalbridge dot com>, Mike Stump <mikestump at comcast dot net>, gcc-patches <gcc-patches at gcc dot gnu dot org>, Lawrence Crowl <crowl at google dot com>, Ian Lance Taylor <iant at google dot com>
- Date: Wed, 24 Apr 2013 15:29:03 +0100
- Subject: Re: patch to fix constant math -5th patch, rtl
- References: <506C72C7 dot 7090207 at naturalbridge dot com> <CAFiYyc1=8=LffiZ=EDBOy_uzn_ARdXk1OWxT=abYd8ot+iFp5Q at mail dot gmail dot com> <50891AAC dot 8090301 at naturalbridge dot com> <CAFiYyc15kmhRWhN3tsZqJDbZ5Uh6tVa45ssiYdsytLEfqaZ4zw at mail dot gmail dot com> <87y5im3orb dot fsf at sandifor-thinkpad dot stglab dot manchester dot uk dot ibm dot com> <CAFiYyc2buJtu8RMKnLnvvb-A2=aYwopO+RBLPO6iJ3gKnq-hvg at mail dot gmail dot com> <87pq3y3kyk dot fsf at sandifor-thinkpad dot stglab dot manchester dot uk dot ibm dot com> <CAFiYyc3NjOxpQ-Y9GDrQOET+dc3LXWuiuM=DxqmyASE8urRoWw at mail dot gmail dot com> <50912D85 dot 1070002 at naturalbridge dot com> <CAFiYyc2Q2UQPmkhExi2c8f-BSGLv+Rq1rOy4NdPQmTqSRE1A0A at mail dot gmail dot com> <5091331C dot 3030504 at naturalbridge dot com> <CAFiYyc1L6zuehE75dEfd_fB1-81F1fDHpL3kS=tbk6qAK3Texg at mail dot gmail dot com> <512D686B dot 90000 at naturalbridge dot com> <515EC4E7 dot 7040907 at naturalbridge dot com> <516DB1F3 dot 8090908 at naturalbridge dot com> <CAFiYyc3P8sFfFQT95yr_UZSOs-JOUefvCm0bxQe1ZSUDgcMg_A at mail dot gmail dot com> <871ua0qer8 dot fsf at sandifor-thinkpad dot stglab dot manchester dot uk dot ibm dot com> <CAFiYyc2kotJXQKT8sWu7UXKd5bYccpZKegMajRSt6BesAx-=ZA at mail dot gmail dot com> <87y5c8nhz2 dot fsf at sandifor-thinkpad dot stglab dot manchester dot uk dot ibm dot com> <CAFiYyc15V9NDk2dAJ9kZZ8wwoxts7bEm5eA5Lk8Tk2Erk9LWKg at mail dot gmail dot com>
Richard Biener <richard.guenther@gmail.com> writes:
> I suppose the above should use immed_double_int_const (v, mode), too,
In practice it doesn't matter, because...
> which oddly only ever truncates to mode for modes <= HOST_BITS_PER_WIDE_INT
> via gen_int_mode.
...right. That's because there's not really any proper support for
non-power-of-2 modes. Partial modes like PDI are specified by things like:
PARTIAL_INT_MODE (DI);
which is glaringly absent of any bit width. So if the constant is big
enough to need 2 HWIs, it in practice must be exactly 2 HWIs wide.
One of the advantages of wide_int is that it allows us to relax this
restriction: we can have both (a) mode widths greater than
HOST_BITS_PER_WIDE_INT*2 and (b) mode widths that are greater than
HOST_BITS_PER_WIDE_INT while not being a multiple of it.
In other words, one of the reasons wide_int can't be exactly 1:1
in practice is because it is clearing out these mistakes (GEN_INT
rather than gen_int_mode) and missing features (non-power-of-2 widths).
Richard