-mstackrealign causes stack corruption on MinGW. And without it the ability
to use SSE instrinsics goes down the drain. Even if we use
__attribute__((force_align_arg_pointer)) for the functions we explicitly
use SSE instrinsics, the SSE code automatically generated by gcc will
cause assertion failures. What a nightmare.
Thankfully LLVM gets this right, so all runtime generated SSE code just
works. rtasm code doesn't assume 16byte alignment. Therefore the bulk of
our performance sensitive code is not affected by this.
Still, intrinsics can be convenient, and it would be nice
to get this working again some day, sp will try to get a reduced test
case.
gprof is useful for shared libraries, hence our drivers. Nevertheless
profilers like oprofile can benefit from disabling some relatively
minor optimizations for more accurate / complete results.
gcc-4.2's optimizer has a strange bug where it looses code from inner
loops in certain situations. For example, if the appearently innocent
looking code below is compiled with gcc-4.2 -S -O1, the inner loop's
code is missing from the outputed assembly.
struct Size {
unsigned width;
};
struct Command {
unsigned length;
struct Size sizes[32];
};
extern void emit_command(void *command, unsigned length);
void
create_surface( struct Size size, unsigned faces, unsigned levels)
{
struct Command cmd;
unsigned face;
unsigned level;
cmd.length = faces*levels*sizeof(cmd.sizes[0]);
for(face = 0; face < faces; ++face) {
for(level = 0; level < levels; ++level) {
cmd.sizes[face*levels + level] = size;
// This should generate a shrl statement, but the whole for body
// disappears in gcc-4.2 -O1/-O2/-O3!
size.width >>= 1;
}
}
emit(&cmd, sizeof cmd.length + cmd.length);
}
Note that this is not specific to MinGW's gcc-4.2 crosscompiler (the
version typically found in debian/ubuntu's mingw32 packages). gcc-4.2 on
Linux also displays the same error. gcc-4.3 and above gets this
correctly though.
Updated MinGW debian packages with gcc-4.3 are available from
http://people.freedesktop.org/~jrfonseca/debian/pool/main/m/
This prevents the error
relocation R_X86_64_PC32 against symbol `_gl_DispatchTSD' can not be used when making a shared object; recompile with -fPIC
when building on x86_64 architecture.
Have to use LINK /LIB instead. The biggest problem is when the command
line is very long and all the options are included in a argument file --
link doesn't like if /LIB is included in the argument file.
José Fonseca
Vinson Lee
Brian Paul
Jakob Bornecrantz
Michel Dänzer
Keith Whitwell