[Bug c++/35585] New: Miscompiled inline assembly
The project I work on uses an inline assembly part to compute floor and ceil functions of floating point numbers and its seems that in some cases, with gcc-4.2 and optimizations turned on, the computed values are not correct. I attached the smallest testcase that I could come up with to reproduce the error and the preprocessed input. Changing the testcase a little suffices to make the miscompilation disappear. Since I am not an expert on inline assembly in gcc, I am not sure that the iCeil/iFloor functions are completely correct and perhaps this is not a bug... I was unable to reproduce the error with gcc-4.1 and gcc-4.3. The error is still present with gcc-4.2.3. The error only appears with -O2/-O3. Compilation command: g++-4.2 -v -save-temps testcase.cpp -o testcase -O3 Using built-in specs. Target: i486-linux-gnu Configured with: ../src/configure -v --enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr --enable-shared --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --enable-nls --with-gxx-include-dir=/usr/include/c++/4.2 --program-suffix=-4.2 --enable-clocale=gnu --enable-libstdcxx-debug --enable-mpfr --enable-targets=all --enable-checking=release --build=i486-linux-gnu --host=i486-linux-gnu --target=i486-linux-gnu Thread model: posix gcc version 4.2.1 (Ubuntu 4.2.1-5ubuntu4) /usr/lib/gcc/i486-linux-gnu/4.2.1/cc1plus -E -quiet -v -D_GNU_SOURCE testcase.cpp -mtune=generic -O3 -fpch-preprocess -o testcase.ii ignoring nonexistent directory /usr/local/include/i486-linux-gnu ignoring nonexistent directory /usr/lib/gcc/i486-linux-gnu/4.2.1/../../../../i486-linux-gnu/include ignoring nonexistent directory /usr/include/i486-linux-gnu #include ... search starts here: #include ... search starts here: /usr/include/c++/4.2 /usr/include/c++/4.2/i486-linux-gnu /usr/include/c++/4.2/backward /usr/local/include /usr/lib/gcc/i486-linux-gnu/4.2.1/include /usr/include End of search list. /usr/lib/gcc/i486-linux-gnu/4.2.1/cc1plus -fpreprocessed testcase.ii -quiet -dumpbase testcase.cpp -mtune=generic -auxbase testcase -O3 -version -fstack-protector -fstack-protector -o testcase.s GNU C++ version 4.2.1 (Ubuntu 4.2.1-5ubuntu4) (i486-linux-gnu) compiled by GNU C version 4.2.1 (Ubuntu 4.2.1-5ubuntu4). GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 Compiler executable checksum: 44e55ae5d2724830dee11801424b84d8 as --traditional-format -V -Qy -o testcase.o testcase.s GNU assembler version 2.18 (i486-linux-gnu) using BFD version (GNU Binutils for Ubuntu) 2.18 /usr/lib/gcc/i486-linux-gnu/4.2.1/collect2 --eh-frame-hdr -m elf_i386 --hash-style=both -dynamic-linker /lib/ld-linux.so.2 -o testcase /usr/lib/gcc/i486-linux-gnu/4.2.1/../../../../lib/crt1.o /usr/lib/gcc/i486-linux-gnu/4.2.1/../../../../lib/crti.o /usr/lib/gcc/i486-linux-gnu/4.2.1/crtbegin.o -L/usr/lib/gcc/i486-linux-gnu/4.2.1 -L/usr/lib/gcc/i486-linux-gnu/4.2.1 -L/usr/lib/gcc/i486-linux-gnu/4.2.1/../../../../lib -L/lib/../lib -L/usr/lib/../lib -L/usr/lib/gcc/i486-linux-gnu/4.2.1/../../.. testcase.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc /usr/lib/gcc/i486-linux-gnu/4.2.1/crtend.o /usr/lib/gcc/i486-linux-gnu/4.2.1/../../../../lib/crtn.o -- Summary: Miscompiled inline assembly Product: gcc Version: 4.2.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: nicos at maunakeatech dot com GCC target triplet: i486-linux-gnu http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35585
[Bug c++/35585] Miscompiled inline assembly
--- Comment #1 from nicos at maunakeatech dot com 2008-03-14 16:26 --- Created an attachment (id=15317) -- (http://gcc.gnu.org/bugzilla/attachment.cgi?id=15317action=view) Testcase to reproduce the bug -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35585
[Bug c++/35585] Miscompiled inline assembly
--- Comment #2 from nicos at maunakeatech dot com 2008-03-14 16:29 --- Created an attachment (id=15318) -- (http://gcc.gnu.org/bugzilla/attachment.cgi?id=15318action=view) Preprocessed testcase -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35585
[Bug c++/35585] Miscompiled inline assembly
--- Comment #4 from nicos at maunakeatech dot com 2008-03-15 01:07 --- I think I need some help here, I looked to bug 323 and I can't see how it is related to this issue. The assertion at the end of the test case compares integers, and the iFloor function is only applied to 0 in the test. My problem is that the result in sp.bbox[0] seems total garbage. I looked at the assembly code generated by gcc (-S flag), the portion corresponding to: sp.bbox[0] = std::min(sp.bbox[0], iFloor(txcum) ); is: .L201: fld %st(1) fadd%st(2), %st fsubs .LC4 #APP fistpl -44(%ebp) #NO_APP movl-44(%ebp), %edi movl-88(%ebp), %eax sarl%edi cmpl16(%ebx), %edi jge .L204 leal-28(%ebp), %eax .L204: fld %st(0) movl(%eax), %eax fadd%st(1), %st fsubs .LC4 movl%eax, 16(%ebx) The result of iFloor is stored in %edi but whatever the result of cmpl, the value in %edi isn't used (instead the value at -28(%ebp), which appears to be uninitialized, is stored into sp.bbox[0]). -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35585
[Bug c++/25260] [4.0/4.1/4.2 Regression] Forward explicit intantiation declaration doesn't mix well with static integral member
--- Comment #3 from nicos at maunakeatech dot com 2005-12-20 09:20 ---
I was under the belief that out of class definitions of const static integral
members was optional for gcc and that static const N = k; was equivalent to
enum { N = k};, was I wrong ?
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25260
[Bug c++/25260] New: Forward explicit intantiation declaration doesn't mix well with static integral member
Compiling:
templateclass T
class A
{
public:
static const unsigned int n = 1;
void foo ()
{
int i = n;
}
};
extern template class Aint;
int main ()
{
Aint a;
a.foo ();
}
fails with:
foo.cpp: In member function 'void AT::foo() [with T = int]':
foo.cpp:9: instantiated from 'const unsigned int Aint::n'
foo.cpp:9: instantiated from 'void AT::foo() [with T = int]'
foo.cpp:18: instantiated from here
foo.cpp:9: error: explicit instantiation of 'Aint::n' but no definition
available
foo.cpp:9: instantiated from 'const unsigned int Aint::n'
foo.cpp:9: instantiated from 'void AT::foo() [with T = int]'
foo.cpp:18: instantiated from here
foo.cpp:9: error: explicit instantiation of 'Aint::n' but no definition
available
--
Summary: Forward explicit intantiation declaration doesn't mix
well with static integral member
Product: gcc
Version: 4.0.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: nicos at maunakeatech dot com
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25260
[Bug c/23077] New: Invalid code with O2 flag (bad alias analysis?)
Source code:
#include stdio.h
int main (int argc, char * argv[])
{
unsigned int t[2] = {1, 1};
*((double *)t) = 0.0;
printf(%d\n, t[1]);
}
This code prints 1 insted of 0 when with: gcc foo.c -o foo -O2
Output of gcc -v foo.c -o foo2 -O2:
Reading specs from /usr/lib/gcc/i686-pc-linux-gnu/3.4.4/specs
Configured with: /var/tmp/portage/gcc-3.4.4/work/gcc-3.4.4/configure
--enable-version-specific-runtime-libs --prefix=/usr
--bindir=/usr/i686-pc-linux-gnu/gcc-bin/3.4.4
--includedir=/usr/lib/gcc/i686-pc-linux-gnu/3.4.4/include
--datadir=/usr/share/gcc-data/i686-pc-linux-gnu/3.4.4
--mandir=/usr/share/gcc-data/i686-pc-linux-gnu/3.4.4/man
--infodir=/usr/share/gcc-data/i686-pc-linux-gnu/3.4.4/info
--with-gxx-include-dir=/usr/lib/gcc/i686-pc-linux-gnu/3.4.4/include/g++-v3
--host=i686-pc-linux-gnu --build=i686-pc-linux-gnu --disable-altivec
--enable-nls --without-included-gettext --with-system-zlib --disable-checking
--disable-werror --disable-libunwind-exceptions --disable-multilib
--disable-libgcj --enable-languages=c,c++,f77 --enable-shared
--enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu
Thread model: posix
gcc version 3.4.4 (Gentoo 3.4.4, ssp-3.4.4-1.0, pie-8.7.8)
/usr/libexec/gcc/i686-pc-linux-gnu/3.4.4/cc1 -quiet -v foo.c -quiet -dumpbase
foo.c -mtune=pentiumpro -auxbase foo -O2 -version -o /tmp/ccFePbg2.s
ignoring nonexistent directory /usr/local/include
ignoring nonexistent directory
/usr/lib/gcc/i686-pc-linux-gnu/3.4.4/../../../../i686-pc-linux-gnu/include
#include ... search starts here:
#include ... search starts here:
/usr/lib/gcc/i686-pc-linux-gnu/3.4.4/include
/usr/include
End of search list.
GNU C version 3.4.4 (Gentoo 3.4.4, ssp-3.4.4-1.0, pie-8.7.8) (i686-pc-linux-gnu)
compiled by GNU C version 3.4.4 (Gentoo 3.4.4, ssp-3.4.4-1.0,
pie-8.7.8).
GGC heuristics: --param ggc-min-expand=90 --param ggc-min-heapsize=113127
/usr/lib/gcc/i686-pc-linux-gnu/3.4.4/../../../../i686-pc-linux-gnu/bin/as -V
-Qy -o /tmp/ccokr9zW.o /tmp/ccFePbg2.s
GNU assembler version 2.16.1 (i686-pc-linux-gnu) using BFD version 2.16.1
/usr/libexec/gcc/i686-pc-linux-gnu/3.4.4/collect2 --eh-frame-hdr -m elf_i386
-dynamic-linker /lib/ld-linux.so.2 -o foo2
/usr/lib/gcc/i686-pc-linux-gnu/3.4.4/../../../crt1.o
/usr/lib/gcc/i686-pc-linux-gnu/3.4.4/../../../crti.o
/usr/lib/gcc/i686-pc-linux-gnu/3.4.4/crtbegin.o
-L/usr/lib/gcc/i686-pc-linux-gnu/3.4.4 -L/usr/lib/gcc/i686-pc-linux-gnu/3.4.4
-L/usr/lib/gcc/i686-pc-linux-gnu/3.4.4/../../../../i686-pc-linux-gnu/lib
-L/usr/lib/gcc/i686-pc-linux-gnu/3.4.4/../../.. /tmp/ccokr9zW.o -lgcc -lgcc_eh
-lc -lgcc -lgcc_eh /usr/lib/gcc/i686-pc-linux-gnu/3.4.4/crtend.o
/usr/lib/gcc/i686-pc-linux-gnu/3.4.4/../../../crtn.o
I suspect that the alias analysis use an incorrect size for double.
--
Summary: Invalid code with O2 flag (bad alias analysis?)
Product: gcc
Version: 3.4.4
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: nicos at maunakeatech dot com
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23077
