On Mon, May 17, 2010 at 3:21 PM, Jack Howarth <howa...@bromo.med.uc.edu> wrote: > On Mon, May 17, 2010 at 02:50:27PM +0200, Richard Guenther wrote: > .... >> >> For example the C++ frontend sets flag_exceptions to 1 but the >> command-line does not contain -fexceptions. Or the Fortran >> frontend might set flag_no_signed_zeros but the command-line >> does not contain -fno-signed-zeros. Similar the Java frontend >> sets flag_wrapv but it's not on the command-line either. >> >> Looking at the command-line for exactly those options we try >> to match (as they change semantics) does not work reliably >> because of that issue. >> >> And for those that would work (optimization options) it doesn't >> really matter (and we don't care at the moment). >> >> The only thing where it might actually work sort-of is for >> target options, but even that's fragile as we don't merge options >> but take those of the first (or last) TU (so if one unit selects >> -msse2 and one -mavx we don't necessarily get -mavx for the >> link step). >> >> Richard. >> > > Richard, > In the case of xplor-nih, there are linkages of shared libraries > which contain a mix of c, c++ and fortran code. In these cases, I am > worried about flags like -fno-second-underscore and -fdefault-integer-8 > which are passed only on FFLAGS. So I guess I need to explicitly look > at the linker command outputted using -v to insure that the proper > flags are being retained. Whether they are actually being passed > properly for the final lto compilations is yet another question.
These are Frontend flags and they should take effect during the compile-stage and thus be not necessary for the link stage. > Jack > ps It would be really nice if lto were smart enough to tag the > lto information in the object files with the some of the optimization > flags such that the lowest common denominator could be used. For > instance, if you had a.o, b.o and c.o where a.o was compiled with -O1, > b.o with -O2 and c.o with -O3, when lto with -fwhole-program tried to > inline between a.o and c.o, the optimization would be dropped to -O1. > Likewise of inlining was shared between b.o and c.o, the optimization > would be dropped to -02. The trick would be to trigger this only in > those cases of inlining so as to not pessimize the code generation > unnecessarily, Well, something would be nice, but not magically choosing something, only complaining if the result won't work as expected. Richard.
