On Tue, Apr 03, 2012 at 07:49:04PM +0100, Richard Sandiford wrote: > Alan Modra <amo...@gmail.com> writes: > > Now that we are back in stage1, I'd like to apply > > http://gcc.gnu.org/ml/gcc-patches/2011-09/msg00304.html, a change to > > toc reference rtl in order to properly specify r2 dependencies. More > > commentary in that url. I'm reposting the patch here since the old > > one no longer applies cleanly, and I've added some ENABLE_CHECKING > > code in rs6000_delegitimize_address. > > Sorry to be a pain, but I don't think HIGH is supposed contain > regs either. Both HIGH and CONST are supposed to be true constants.
Eh, so the existing use of CONST is wrong then. ;-) I'm proposing (unspec [(symbol_ref sym) (reg r2)] UNSPEC_TOCREL) for the small model, and (high (unspec [(symbol_ref sym) (reg r2)] UNSPEC_TOCREL))) (lo_sum (reg hi) (unspec [(symbol_ref sym) (reg r2)] UNSPEC_TOCREL)) for medium/large model. You can see why I'd like to keep it this way; The medium/large rtl is a natural split of the small rtl. (I'm going to experiment with splitting the small rtl after reload for medium/large to see whether that helps our usage of call-saved regs in loops.) I'm not wedded to the representation, *but* we do want gcc to treat the high part as a constant. That's important because we don't ever want reload saving the high part to a stack slot! Which is what does happen if you don't somehow tell gcc it is a constant. Besides, the high part *is* a constant within any given function. So is the low part for that matter. The only reason I want r2 mentioned in this rtl is for register liveness, eg. so that a load of a function pointer (which loads r2) for an indirect call doesn't get scheduled before any uses of the old r2. The alternative of removing r2 from the unspec and attaching a (use (reg r2)) to all instructions that have this addressing form might be clean but will require major duplication of patterns in rs6000.md, won't it? -- Alan Modra Australia Development Lab, IBM
