On 17 Sep 14:12, Jakub Jelinek wrote: > On Tue, Sep 17, 2013 at 01:56:39PM +0200, Richard Biener wrote: > > > > Are you sure we have the same IL for all targets and the same targets > > for all functions? That would certainly simplify things, but you still need > > a way to tell the target compiler which symbol to emit the function on > > as the compile-stage will already necessarily refer to all target > > variant symbols. > > This has been discussed to some extent during Cauldron. > Yes, there are various target dependencies in the GIMPLE IL, many of them > very early. > Some of the dependencies are there already during preprocessing, there is > nothing to do about those. > For some things we will just rely on the host and target having the same > properties, stuff like BITS_PER_UNIT, type layout/alignment, endianity, > the OpenMP (and I believe OpenACC too) model effectively requires that, > while you don't need to have shared address space between host and target > (but can have that), for the mapping/unmapping it is assumed that you can > simply take host portions of memory and copy them over to the target device > or back, as sequence of bytes, there is no form of RPC or similar that would > tweak endianity, differently sized types, padding, etc. > While you can say have 64-bit host and 32-bit target or vice versa, the > target IL will simply contain precision info, alignment, structure layout > etc. and just will have to generate right code for that (something that is > native long on the host can be native long long on the target or vice versa > etc.). > Then there are dependencies we'd ideally get rid of, at least pre-IPA, > stuff like BRANCH_COST, but generally that is just an optimization issue and > thus not that big deal. > Bigger issue are target specific builtins, I guess we'll either have to just > sorry on those, or have some helper targhook that will translate a subset of > md builtins from selected hosts to selected targets. > Preferrably, before IPA we'd introduce as few target dependencies into the > IL as possible, and gradually towards RTL can add more dependencies (e.g. > the vectorizer adds so many target dependencies that at that point trying to > use the IL for a different target is practically impossible). > > Jakub
Do I understand correctly that GIMPLE IL is target dependent, but we will emit the same IL for all targets? -- Ilya
