https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117305
Bug ID: 117305
Summary: include files processed differently depending on
directory they were fetched from
Product: gcc
Version: 14.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: joakim.rosqvist at gmail dot com
Target Milestone: ---
Hi.
(I know the reporting instruction says not to submit .h files but I need to do
that as it is the processing of them that seems to be the issue)
The included test program rotates a 64 bit integer a number of steps determined
by the variable d, whose value is not defined in the program. Thus, a warning
about an uninitialized variable is expected.
The rotate function is normally defined in <immintrin.h>. For brevity I have
extracted the relevant parts in myia32intrin.h:
#define _lrotl(a,b) __rolq((a), (b))
unsigned long long __rolq (unsigned long long __X, int __C)
{
__C &= 63;
return (__X << __C) | (__X >> (-__C & 63));
}
The C program that uses the above include file looks like so (foo.c):
#include "myia32intrin.h"
int main(int , char *[])
{
int d;
return _lrotl(1, d+1);
}
Let's compile it:
>gcc -O -Wuninitialized -o foo foo.c
myia32intrin.h:2:33: warning: ‘d’ is used uninitialized [-Wuninitialized]
2 | #define _lrotl(a,b) __rolq((a), (b))
| ^~~~~~~~~~~~~~~~
foo.c:7:12: note: in expansion of macro ‘_lrotl’
7 | return _lrotl(1, d+1);
| ^~~~~~
foo.c:5:9: note: ‘d’ was declared here
5 | int d;
| ^
Indeed, I did get the expected warning about 'd' being used uninitialized.
However, now I move myia32intrin.h to
/usr/lib/gcc/x86_64-linux-gnu/14/include/ (i.e. where <immintrin.h> an friends
live) and change the C program to find the include file among the system
headers by using angle brackets:
#include <myia32intrin.h>
int main(int , char *[])
{
int d;
return _lrotl(1, d+1);
}
And then compile again as above:
>gcc -O -Wuninitialized -o foo foo.c
This time there is no warning about the uninitialized variable!
Here is the preprocessed C file in the case where I include a local file and do
get a warning (foo_works.i):
# 0 "foo.c"
# 0 "<built-in>"
# 0 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 0 "<command-line>" 2
# 1 "foo.c"
# 1 "myia32intrin.h" 1
unsigned long long __rolq (unsigned long long __X, int __C)
{
__C &= 63;
return (__X << __C) | (__X >> (-__C & 63));
}
# 2 "foo.c" 2
int main(int , char *[])
{
int d;
return __rolq((1), (d+1));
}
And here is the preprocessed C file in the case where I include a system header
file and don't get a warning (foo_fail.i):
# 0 "foo.c"
# 0 "<built-in>"
# 0 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 0 "<command-line>" 2
# 1 "foo.c"
# 1 "/usr/lib/gcc/x86_64-linux-gnu/14/include/myia32intrin.h" 1 3 4
# 4 "/usr/lib/gcc/x86_64-linux-gnu/14/include/myia32intrin.h" 3 4
unsigned long long __rolq (unsigned long long __X, int __C)
{
__C &= 63;
return (__X << __C) | (__X >> (-__C & 63));
}
# 2 "foo.c" 2
# 3 "foo.c"
int main(int , char *[])
{
int d;
return
# 7 "foo.c" 3 4
__rolq((
# 7 "foo.c"
1
# 7 "foo.c" 3 4
), (
# 7 "foo.c"
d+1
# 7 "foo.c" 3 4
))
# 7 "foo.c"
;
}
Finally, the output of gcc -v:
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-linux-gnu/14/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 14.2.0-4ubuntu2'
--with-bugurl=file:///usr/share/doc/gcc-14/README.Bugs
--enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2,rust --prefix=/usr
--with-gcc-major-version-only --program-suffix=-14
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/libexec --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-libstdcxx-backtrace
--enable-gnu-unique-object --disable-vtable-verify --enable-plugin
--enable-default-pie --with-system-zlib --enable-libphobos-checking=release
--with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch
--disable-werror --enable-cet --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none=/build/gcc-14-zdkDXv/gcc-14-14.2.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-14-zdkDXv/gcc-14-14.2.0/debian/tmp-gcn/usr
--enable-offload-defaulted --without-cuda-driver --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
--with-build-config=bootstrap-lto-lean --enable-link-serialization=2
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 14.2.0 (Ubuntu 14.2.0-4ubuntu2)
