From: Richard Sandiford <rdsandiford@googlemail.com>
To: Mikael Pettersson <mikpe@it.uu.se>
Cc: John David Anglin <dave.anglin@nrc-cnrc.gc.ca>,
Eric Botcazou <ebotcazou@adacore.com>,
gcc-patches@gcc.gnu.org
Subject: Re: [5/8] Tweak bitfield alignment handling
Date: Tue, 20 Nov 2012 10:32:00 -0000 [thread overview]
Message-ID: <87y5hwva2d.fsf@sandifor-thinkpad.stglab.manchester.uk.ibm.com> (raw)
In-Reply-To: <20651.15580.299904.594975@pilspetsen.it.uu.se> (Mikael Pettersson's message of "Tue, 20 Nov 2012 09:18:36 +0100")
Mikael Pettersson <mikpe@it.uu.se> writes:
> John David Anglin writes:
> > On Sun, 18 Nov 2012, Richard Sandiford wrote:
> >
> > > HOST_WIDE_INT start = bitpos_ - (bitpos_ % unit);
> > > if (bitregion_start_ && start < bitregion_start_)
> > > break;
> > > - if (bitregion_end_ && start + unit > bitregion_end_ + 1)
> > > + if (start + unit > bitregion_end_ + 1)
> >
> > This causes:
> >
> > /home/dave/gnu/gcc/objdir/./prev-gcc/g++ -B/home/dave/gnu/gcc/objdir/./prev-gcc/ -B/home/dave/opt/gnu/gcc/gcc-4.8.0/hppa-linux-gnu/bin/ -nostdinc++ -B/home/dave/gnu/gcc/objdir/prev-hppa-linux-gnu/libstdc++-v3/src/.libs -B/home/dave/gnu/gcc/objdir/prev-hppa-linux-gnu/libstdc++-v3/libsupc++/.libs -I/home/dave/gnu/gcc/objdir/prev-hppa-linux-gnu/libstdc++-v3/include/hppa-linux-gnu -I/home/dave/gnu/gcc
> > /objdir/prev-hppa-linux-gnu/libstdc++-v3/include -I/home/dave/gnu/gcc/gcc/libstdc++-v3/libsupc++ -L/home/dave/gnu/gcc/objdir/prev-hppa-linux-gnu/libstdc++-v3/sr
> > c/.libs -L/home/dave/gnu/gcc/objdir/prev-hppa-linux-gnu/libstdc++-v3/libsupc++/.libs -c -g -O2 -DIN_GCC -fno-exceptions -fno-rtti -fasynchronous-unwind-tabl
> > es -W -Wall -Wno-narrowing -Wwrite-strings -Wcast-qual -Wmissing-format-attribut
> > e -pedantic -Wno-long-long -Wno-variadic-macros -Wno-overlength-strings -Werror
> > -fno-common -DHAVE_CONFIG_H -I. -I. -I../../gcc/gcc -I../../gcc/gcc/. -I../../g
> > cc/gcc/../include -I../../gcc/gcc/../libcpp/include -I../../gcc/gcc/../libdecnu
> > mber -I../../gcc/gcc/../libdecnumber/dpd -I../libdecnumber -I../../gcc/gcc/../li
> > bbacktrace ../../gcc/gcc/stor-layout.c -o stor-layout.o../../gcc/gcc/stor-layout.c: In member function 〘bool bit_field_mode_iterator::n
> > ext_mode(machine_mode*)〙:
> > ../../gcc/gcc/stor-layout.c:2690:43: error: comparison between signed and unsign
> > ed integer expressions [-Werror=sign-compare]
> > if (start + unit > bitregion_end_ + 1)
> > ^
> > cc1plus: all warnings being treated as errors
>
> This error also breaks m68k-linux bootstrap.
>
> HWI32 issue?
Yeah, I expect so, sorry.
Logically, everything here would be unsigned arithmetic, but as the
comment says:
/* We use signed values here because the bit position can be negative
for invalid input such as gcc.dg/pr48335-8.c. */
This is the patch I'm testing. There are three things being checked here:
- "unit", the size of the mode in isolation. This really is an unsigned
value, and is compared to unsigned values like GET_MODE_PRECISION.
- bitpos_ % unit (+ bitsize_), the start and end positions of the bitfield
relative to the start of the mode. The start position is supposed to be
[0, unit), so the modulus and result should be unsigned. (Using unsigned
modulus doesn't cope with negative bit positions combined with
non-power-of-2 units, but I don't think we support that.)
- bitregion_start_ and bitregion_end_. bitpos_ is signed and can be
negative, so the bitregion comparison should continue to be signed.
OK to commit if testing succeeds?
Richard
gcc/
* stor-layout.c (bit_field_mode_iterator::next_mode): Fix signedness.
Index: gcc/stor-layout.c
===================================================================
--- gcc/stor-layout.c 2012-11-20 10:15:39.000000000 +0000
+++ gcc/stor-layout.c 2012-11-20 10:15:39.464712715 +0000
@@ -2670,10 +2670,6 @@ bit_field_mode_iterator::next_mode (enum
if (unit != GET_MODE_PRECISION (mode_))
continue;
- /* Skip modes that are too small. */
- if ((bitpos_ % unit) + bitsize_ > unit)
- continue;
-
/* Stop if the mode is too wide to handle efficiently. */
if (unit > MAX_FIXED_MODE_SIZE)
break;
@@ -2683,11 +2679,18 @@ bit_field_mode_iterator::next_mode (enum
if (count_ > 0 && unit > BITS_PER_WORD)
break;
+ /* Skip modes that are too small. */
+ unsigned HOST_WIDE_INT substart = (unsigned HOST_WIDE_INT) bitpos_ % unit;
+ unsigned HOST_WIDE_INT subend = substart + bitsize_;
+ if (subend > unit)
+ continue;
+
/* Stop if the mode goes outside the bitregion. */
- HOST_WIDE_INT start = bitpos_ - (bitpos_ % unit);
+ HOST_WIDE_INT start = bitpos_ - substart;
if (bitregion_start_ && start < bitregion_start_)
break;
- if (start + unit > bitregion_end_ + 1)
+ HOST_WIDE_INT end = start + unit;
+ if (end > bitregion_end_ + 1)
break;
/* Stop if the mode requires too much alignment. */
next prev parent reply other threads:[~2012-11-20 10:32 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-03 11:10 [0/8] Add optabs alternatives for insv, extv and extzv Richard Sandiford
2012-11-03 11:13 ` [1/8] Handle TRUNCATE in make_extraction Richard Sandiford
2012-11-10 15:52 ` Eric Botcazou
2012-11-03 11:14 ` [2/8] Add adjust_bitfield_address_size Richard Sandiford
2012-11-10 15:53 ` Eric Botcazou
2012-11-03 11:16 ` [3/8] Add narrow_bit_field_mem Richard Sandiford
2012-11-10 16:02 ` Eric Botcazou
2012-11-03 11:21 ` [4/8] Add bit_field_mode_iterator Richard Sandiford
2012-11-13 12:44 ` Eric Botcazou
2012-11-13 21:46 ` Richard Henderson
2012-11-13 22:05 ` Eric Botcazou
2012-11-15 12:11 ` Richard Sandiford
2012-11-15 20:39 ` Richard Henderson
2012-11-18 17:34 ` Richard Sandiford
2012-11-18 17:36 ` Richard Sandiford
2012-11-03 11:27 ` [5/8] Tweak bitfield alignment handling Richard Sandiford
2012-11-13 13:52 ` Eric Botcazou
2012-11-18 17:36 ` Richard Sandiford
2012-11-20 2:57 ` John David Anglin
2012-11-20 8:21 ` Mikael Pettersson
2012-11-20 10:32 ` Richard Sandiford [this message]
2012-11-20 19:56 ` Richard Sandiford
2012-11-20 22:11 ` Eric Botcazou
2012-11-03 11:28 ` [6/8] Add strict volatile handling to bit_field_mode_iterator Richard Sandiford
2012-11-13 13:57 ` Eric Botcazou
2012-11-15 12:25 ` Richard Sandiford
2012-11-15 17:10 ` Eric Botcazou
2012-11-15 17:47 ` Richard Sandiford
2012-11-15 19:32 ` Eric Botcazou
2012-11-18 17:36 ` Richard Sandiford
2012-11-03 11:39 ` [7/8] Replace mode_for_extraction with new interface Richard Sandiford
2012-11-03 11:41 ` [8/8] Add new optabs and use them for MIPS Richard Sandiford
2012-11-27 17:11 ` [0/8] Add optabs alternatives for insv, extv and extzv Ramana Radhakrishnan
2012-11-27 20:22 ` Richard Sandiford
2012-11-27 22:45 ` Ramana Radhakrishnan
2012-11-28 10:25 ` Richard Biener
2012-11-28 12:06 ` Ramana Radhakrishnan
2012-11-28 12:51 ` Richard Biener
2012-11-28 13:58 ` Richard Sandiford
2012-11-28 23:19 ` Eric Botcazou
2012-11-29 10:31 ` Richard Sandiford
2012-11-29 15:31 ` Eric Botcazou
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87y5hwva2d.fsf@sandifor-thinkpad.stglab.manchester.uk.ibm.com \
--to=rdsandiford@googlemail.com \
--cc=dave.anglin@nrc-cnrc.gc.ca \
--cc=ebotcazou@adacore.com \
--cc=gcc-patches@gcc.gnu.org \
--cc=mikpe@it.uu.se \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).