[Bug c/41673] New: 4.5.0 20091008 variable-length array dereference inside sizeof gives "warning: dereferencing type-punned pointer will break strict-aliasing rules"
A variable-length array pointer 'dereference' inside sizeof() is causing GCC to
give an aliasing warning. I can think of no reason why completely
compiletime-static sizeof() activity could create an aliasing violation.
I've included a contrived example showing 4.5.0 producing the warning while
4.4.1 does not complain:
[gmaxw...@floodlamp tmp]$ cat test.c
#include
int main(int argc, char *argv[])
{
float x[argc];
float y[argc];
return NULL == memcpy(y, x, argc * sizeof(*x));
}
[gmaxw...@floodlamp tmp]$ /usr/local/bin/gcc -std=gnu99 -O2 -Wall -o test
test.c
test.c: In function main:
test.c:6:5: warning: dereferencing type-punned pointer will break
strict-aliasing rules
[gmaxw...@floodlamp tmp]$ /usr/local/bin/gcc -v
Using built-in specs.
COLLECT_GCC=/usr/local/bin/gcc
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-unknown-linux-gnu/4.5.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ./configure --with-ppl --with-cloog --with-gmp --enable-lto
Thread model: posix
gcc version 4.5.0 20091008 (experimental) (GCC)
[gmaxw...@floodlamp tmp]$ /usr/bin/gcc -std=gnu99 -O2 -Wall -o test test.c
[gmaxw...@floodlamp tmp]$ /usr/bin/gcc -v
Using built-in specs.
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla
--enable-bootstrap --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk
--disable-dssi --enable-plugin
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--enable-libgcj-multifile --enable-java-maintainer-mode
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib
--with-ppl --with-cloog --with-tune=generic --with-arch_32=i586
--build=x86_64-redhat-linux
Thread model: posix
gcc version 4.4.1 20090725 (Red Hat 4.4.1-2) (GCC)
The -O2 plus sizeof(*x) anywhere where x is a var-array is necessary and
sufficient to trigger this. Switching to a statically sized array avoids the
warning.
The actual use-case where I hit this is where sizeof() is used in this manner
when a type is selected by some compile time configuration and manually
restating the type in sizeof() would require a great many more ifdefs.
--
Summary: 4.5.0 20091008 variable-length array dereference inside
sizeof gives "warning: dereferencing type-punned pointer
will break strict-aliasing rules"
Product: gcc
Version: 4.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: gmaxwell at gmail dot com
GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41673
[Bug c/50286] New: Missed optimization, fails to propagate bool
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50286
Bug #: 50286
Summary: Missed optimization, fails to propagate bool
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: minor
Priority: P3
Component: c
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: gmaxw...@gmail.com
GCC 4.7.0 (and prior) are unable to determine maximum loop counts in code that
looks like:
#include
int main(int argc, char **argv)
{
int i;
const int flag=argc>1;
i=0;
do{
printf("%d\n",i*i);
}while(++i<1+flag);
return 0;
}
and so it doesn't unroll the loop.
If 1+flag is changed to 1+!!flag, 1+(bool)flag, or 1+(argc>1) then -O3 unrolls
the loop.
Interestingly, making flag type bool doesn't fix it and also doesn't unroll in
the 1+!!flag case.
[Bug middle-end/50333] New: internal compiler error: in extract_ops_from_tree, at gimple.h:1909
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50333 Bug #: 50333 Summary: internal compiler error: in extract_ops_from_tree, at gimple.h:1909 Classification: Unclassified Product: gcc Version: 4.7.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: middle-end AssignedTo: unassig...@gcc.gnu.org ReportedBy: gmaxw...@gmail.com Created attachment 25230 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25230 trigger case Compiling libopus http://git.xiph.org/?p=opus.git;a=snapshot;h=f329fa6f0f1e08506a210608bc6de34b5949ec6b;sf=tgz libcelt/cwrs.c: In function 'encode_pulses': libcelt/cwrs.c:589:6: internal compiler error: in extract_ops_from_tree, at gimple.h:1909 $ gcc -v Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/home/gmaxwell/gcc/libexec/gcc/x86_64-unknown-linux-gnu/4.7.0/lto-wrapper Target: x86_64-unknown-linux-gnu Configured with: ./configure --enable-lto --prefix=/home/gmaxwell/gcc/ --enable-cloog-backend=isl --disable-java --disable-libgcj --enable-lipo --enable-graphite --enable-languages=c --disable-bootstrap --enable-stage1-languages=c --disable-libstdcxx-v3 Thread model: posix gcc version 4.7.0 20110908 (experimental) (GCC) CFLAGS='-O2 -ftree-vectorize' ; make (-O3 fails too, -O2 + -ftree-vectorize seems to me the minimal failure case) Preprocessed file attached.
[Bug middle-end/50335] New: ICE in psct_dynamic_dim, at graphite-poly.h:659
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50335 Bug #: 50335 Summary: ICE in psct_dynamic_dim, at graphite-poly.h:659 Classification: Unclassified Product: gcc Version: 4.7.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: middle-end AssignedTo: unassig...@gcc.gnu.org ReportedBy: gmaxw...@gmail.com Created attachment 25231 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25231 preprocessed case that reproduces it Compiling libopus http://git.xiph.org/?p=opus.git;a=snapshot;h=f329fa6f0f1e08506a210608bc6de34b5949ec6b;sf=tgz libcelt/pitch.c: In function 'pitch_search': libcelt/pitch.c:152:6: internal compiler error: in psct_dynamic_dim, at graphite-poly.h:659 $ gcc -v Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/home/gmaxwell/gcc/libexec/gcc/x86_64-unknown-linux-gnu/4.7.0/lto-wrapper Target: x86_64-unknown-linux-gnu Configured with: ./configure --enable-lto --prefix=/home/gmaxwell/gcc/ --enable-cloog-backend=isl --disable-java --disable-libgcj --enable-lipo --enable-graphite --enable-languages=c --disable-bootstrap --enable-stage1-languages=c --disable-libstdcxx-v3 Thread model: posix gcc version 4.7.0 20110908 (experimental) (GCC) CFLAGS='-Ofast -floop-flatten' ; make (doesn't fail with -O3 -floop-flatten) Preprocessed file attached.
[Bug middle-end/50335] ICE in psct_dynamic_dim, at graphite-poly.h:659
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50335 --- Comment #1 from Gregory Maxwell 2011-09-17 00:31:43 UTC --- Still failing in r178925.
[Bug middle-end/50335] ICE in psct_dynamic_dim, at graphite-poly.h:659
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50335 --- Comment #2 from Gregory Maxwell 2011-10-07 14:52:37 UTC --- Still failing in r179659.
[Bug middle-end/50335] ICE in psct_dynamic_dim, at graphite-poly.h:659
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50335 --- Comment #4 from Gregory Maxwell 2011-10-07 15:29:42 UTC --- Ha, indeed. Well, I don't want it to be forgotten just because its become old and potentially inapplicable. I test GCC development periodically on all the software I work on— most of the time anything I find is fixed quickly, it's not something urgent for me. (I once reported a bug in a proprietary compiler: reporting bugs in GCC is my penance ;) )
[Bug middle-end/50335] ICE in psct_dynamic_dim, at graphite-poly.h:659
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50335 --- Comment #11 from Gregory Maxwell 2012-02-14 17:15:23 UTC --- Still crashing in, r184217.
[Bug middle-end/50335] ICE in psct_dynamic_dim, at graphite-poly.h:659
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50335 --- Comment #12 from Gregory Maxwell 2012-02-22 09:19:54 UTC --- _Not_ failing in r184458. Perhaps fixed by r184265?
[Bug middle-end/50335] ICE in psct_dynamic_dim, at graphite-poly.h:659
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50335 --- Comment #13 from Gregory Maxwell 2012-02-22 09:39:51 UTC --- Okay, it doesn't ICE now— but now I have cases where it apparently runs forever and cases where it produces incorrect code with -floop-flatten.
[Bug middle-end/50335] ICE in psct_dynamic_dim, at graphite-poly.h:659
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50335 --- Comment #5 from Gregory Maxwell 2011-11-14 06:19:44 UTC --- Still failing with r181345
[Bug middle-end/50335] ICE in psct_dynamic_dim, at graphite-poly.h:659
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50335 --- Comment #6 from Gregory Maxwell 2011-12-06 04:51:47 UTC --- Still failing in r182038
