Current mainline gcc appears to miscompile the following code: ======begin======
static void foo (double a, double weight, const double *ring, double *phase) { *phase = *ring * weight; } static void foo2 (void) { foo (0, 1, (double*)0, (double*)0); } static void foo3 (void) { foo2(); } void foo4 (void) { foo3(); } int main(void) { double t1=1, c1; foo(0,1,&t1,&c1); return (c1>0.5) ? 1:0; } =======end======= /scratch/martin/libpsht-0.2>gcc -v -O -ffast-math psht_test.c -lm Using built-in specs. Target: i686-pc-linux-gnu Configured with: /scratch/martin/gcc/configure --prefix=/afs/mpa/data/martin/ugcc --enable-languages=c --enable-checking=release Thread model: posix gcc version 4.3.0 20061115 (experimental) /afs/mpa/data/martin/ugcc/libexec/gcc/i686-pc-linux-gnu/4.3.0/cc1 -quiet -v psht_test.c -quiet -dumpbase psht_test.c -mtune=generic -auxbase psht_test -O -version -ffast-math -o /tmp/ccSNsfEN.s ignoring nonexistent directory "/afs/mpa/data/martin/ugcc/lib/gcc/i686-pc-linux-gnu/4.3.0/../../../../i686-pc-linux-gnu/include" #include "..." search starts here: #include <...> search starts here: /usr/local/include /afs/mpa/data/martin/ugcc/include /afs/mpa/data/martin/ugcc/lib/gcc/i686-pc-linux-gnu/4.3.0/include /usr/include End of search list. GNU C version 4.3.0 20061115 (experimental) (i686-pc-linux-gnu) compiled by GNU C version 4.3.0 20061115 (experimental). GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 Compiler executable checksum: e4c043f86c42a15259a6956a912800d1 as -V -Qy -o /tmp/cc424C9p.o /tmp/ccSNsfEN.s GNU assembler version 2.16.1 (i686-pc-linux-gnu) using BFD version 2.16.1 /afs/mpa/data/martin/ugcc/libexec/gcc/i686-pc-linux-gnu/4.3.0/collect2 --eh-frame-hdr -m elf_i386 -dynamic-linker /lib/ld-linux.so.2 /usr/lib/crt1.o /usr/lib/crti.o /afs/mpa/data/martin/ugcc/lib/gcc/i686-pc-linux-gnu/4.3.0/crtbegin.o -L/afs/mpa/data/martin/ugcc/lib/gcc/i686-pc-linux-gnu/4.3.0 -L/afs/mpa/data/martin/ugcc/lib/gcc/i686-pc-linux-gnu/4.3.0/../../.. /tmp/cc424C9p.o -lm -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /afs/mpa/data/martin/ugcc/lib/gcc/i686-pc-linux-gnu/4.3.0/crtfastmath.o /afs/mpa/data/martin/ugcc/lib/gcc/i686-pc-linux-gnu/4.3.0/crtend.o /usr/lib/crtn.o /scratch/martin/libpsht-0.2>./a.out /scratch/martin/libpsht-0.2>echo $? 0 The correct exit code would be 1. I did some regression hunting, and the problem appears to have been introduced to SVN with revision 118859 (introduction of -mx87regparm by Uros Bizjak). The compiled code behaves correctly if - the "-ffast-math" flag is omitted, and/or - the functions foo2() - foo4() (which are not called anyway) are removed -- Summary: silent miscompilation of argument passing(?) Product: gcc Version: 4.3.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: martin at mpa-garching dot mpg dot de 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=30120