On Sat, 19 Nov 2005, Chris Lattner wrote: > This is a direct result of the representation that you are proposing to use > for IPA. LLVM is *always* capable of merging two translation units correctly,
So compilation options which change the semantics of GIMPLE are translated into local flags on the relevant code in LLVM (or failing that combined to the most conservative settings, but not all such options have such settings) - or it will be extended so that they are? Examples: -ftrapv -fwrapv -fno-math-errno -funsafe-math-optimizations -funsafe-loop-optimizations -ffinite-math-only -fno-trapping-math -frounding-math -ffloat-store -fsignaling-nans -fcx-limited-range. That sounds good if so; good implementation of C99 pragmas requires some of these settings to be appliable locally to particular blocks of code, which we don't currently have the infrastructure to do. (*Any* combining of separately compiled translation units needs some way to deal with this problem - semantics depending on global variables - as well as for the places where the semantics of GIMPLE depend on langhooks which are different for different languages. Of course all globals and hooks should be audited for such implicit effect on semantics.) That said, while in cases of such different options combining is desirable, there are cases where refusing to combine is a feature not a bug - if the user program can be detected to have incompatible translation units (e.g. where the same named function takes different types of arguments) then telling the user is useful, and if the program has some of the stranger combinations of types that may or may not be valid in C (DR#314 and subsequent discussion in Mt Tremblant minutes) then diagnosing this is also useful. Of course it's not the optimizer's job to diagnose such things, but infrastructure to diagnose them (possibly quite separate from that for optimization) can be useful. -- Joseph S. Myers http://www.srcf.ucam.org/~jsm28/gcc/ [EMAIL PROTECTED] (personal mail) [EMAIL PROTECTED] (CodeSourcery mail) [EMAIL PROTECTED] (Bugzilla assignments and CCs)
