[Bug c/56977] New: gcc -Og incorrectly warns about 'constant zero length parameter'

[baugesta at cisco dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56977

 Bug #: 56977
   Summary: gcc -Og incorrectly warns about 'constant zero length
parameter'
Classification: Unclassified
   Product: gcc
   Version: 4.8.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: bauge...@cisco.com


Created attachment 29881
  -- http://gcc.gnu.org/bugzilla/attachment.cgi?id=29881
Preprocessed version of snippet in the Description field.

Compiling this tiny snippet with the command 'gcc -v -Og' produces an incorrect
warning about zero length parameter:

#include string.h

void foo(char *buf, size_t w, size_t h)
{
size_t n = w * h;
if (n  0)
memset(buf, 123, n);
}

The warning looks like this:
/usr/include/bits/string3.h:81:30: warning: call to ‘__warn_memset_zero_len’
declared with attribute warning: memset used with constant zero length
parameter; this could be due to transposed parameters [enabled by default]
   __warn_memset_zero_len ();


Output from gcc -v:
$ gcc -v
Using built-in specs.
COLLECT_GCC=/usr/x86_64-pc-linux-gnu/gcc-bin/4.8.0/gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/4.8.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /var/tmp/portage/sys-devel/gcc-4.8.0/work/gcc-4.8.0/configure
--prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/4.8.0
--includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.8.0/include
--datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.8.0
--mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.8.0/man
--infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.8.0/info
--with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.8.0/include/g++-v4
--host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --disable-altivec
--disable-fixed-point --without-ppl --without-cloog --enable-lto --enable-nls
--without-included-gettext --with-system-zlib --enable-obsolete
--disable-werror --enable-secureplt --enable-multilib
--with-multilib-list=m32,m64 --enable-libmudflap --disable-libssp
--enable-libgomp
--with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/4.8.0/python
--enable-checking=release --disable-libgcj --enable-libstdcxx-time
--disable-libquadmath --enable-languages=c,c++,objc --enable-shared
--enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu
--enable-targets=all --with-bugurl=http://bugs.gentoo.org/
--with-pkgversion='Gentoo 4.8.0 p1.1, pie-0.5.5'
Thread model: posix
gcc version 4.8.0 (Gentoo 4.8.0 p1.1, pie-0.5.5)

[Bug c/52326] New: float result incorrect with -O1 and calling external function.

[baugesta at cisco dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52326

 Bug #: 52326
   Summary: float result incorrect with -O1 and calling external
function.
Classification: Unclassified
   Product: gcc
   Version: 4.6.2
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: bauge...@cisco.com


Created attachment 26713
  -- http://gcc.gnu.org/bugzilla/attachment.cgi?id=26713
Two source files, one header file and a Makefile

The sample program attached fails when built with -O1, but not with any other
optimization levels (0,2,3). Unfortunately it only fails when we call an
external function, therefore we had to attach a tgz file instead of a
preprocessed file. 

The tar file contains four files: main.c, foo.c, foo.h and a Makefile. The 
Makefile, which builds two targets (fail and success) can be used to re-create
the problem as well as to build a non-failing version. 

Also, the error only occurs when certain other conditions are met. We've
written a C comment for every condition we found in the source file named
main.c. Please search for the text NOTE. 

GCC Version:

Our GCC version is 4.6.2. It fails on multiple versions/builds of 4.6.2, both
the one provided with Gentoo and the one provided by Centos 6. The info below
is from my Gentoo host:

COLLECT_GCC=/usr/x86_64-pc-linux-gnu/gcc-bin/4.6.2/gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/4.6.2/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /var/tmp/portage/sys-devel/gcc-4.6.2/work/gcc-4.6.2/configure
--prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/4.6.2
--includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.6.2/include
--datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.6.2
--mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.6.2/man
--infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.6.2/info
--with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.6.2/include/g++-v4
--host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --disable-altivec
--disable-fixed-point --without-ppl --without-cloog --enable-lto --enable-nls
--without-included-gettext --with-system-zlib --disable-werror
--enable-secureplt --enable-multilib --enable-libmudflap --disable-libssp
--enable-libgomp
--with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/4.6.2/python
--enable-checking=release --disable-libgcj --disable-libquadmath
--enable-languages=c,c++ --enable-shared --enable-threads=posix
--enable-__cxa_atexit --enable-clocale=gnu --enable-targets=all
--with-bugurl=http://bugs.gentoo.org/ --with-pkgversion='Gentoo 4.6.2 p1.4,
pie-0.5.0'
Thread model: posix
gcc version 4.6.2 (Gentoo 4.6.2 p1.4, pie-0.5.0) 

The complete command line that triggers the bug:

gcc -o fail -O1 -Wall -Wextra -Wconversion -Werror -Wshadow
-Wmissing-declarations -std=c89 main.c foo.c  ./fail

(Note that it also fails with less arguments, -O1 is all it takes)

Compiler output:
---
None


Preprocessed file:
--
Due to the nature of the bug, calling an external function, we could not
provide a preprocessed file.