On Thursday 2 August 2007 02:55:57 Chris Lattner wrote: > > On Jul 31, 2007, at 3:08 PM, Evan Cheng wrote: > > >>> Also, isn't the static chain register described in > >>> X86CallingConv.td? > >> > >> It is, but it's hard to use here. The problem is that when > >> lowering the > >> init.trampoline intrinsic you only have a pointer to the target > >> function. > >> From this pointer you would like to find out which register a certain > >> parameter will be passed in for that function. Not so easy! It's > >> like > >> having a call instruction without having the arguments. In order to > >> exploit X86CallingConv.td, you have to use all the lowering > >> machinery, > >> which isn't adapted to this case. For example, you could try to > >> synthesize > >> a fake call. Or you could pretend to be lowering the target > >> function. I > >> tried it, and it can be done with a lot of horrible hacking. But > >> it's not > >> worth it. It's much simpler to simply grab the calling convention > >> and use > >> that, which unfortunately means keeping LowerTRAMPOLINE and > >> X86CallingConv.td in sync. Personally I can live with that, > >> especially since > >> I've seen the alternative and it still wakes me up screaming at > >> night :) > >> But maybe you can see a reasonable way of doing it? > > > > Seems like a deficiency in CCState class. Chris, your thoughts? > > Isn't the argument always a pointer, and thus always the same thing > for a particular calling conv?
It is, but that's not the problem: the problem is that you need to know how the *other* arguments are lowered in order to know whether there was a register left for the static chain argument, or whether an argument that would have been passed in a register if the static chain wasn't there is not passed in a register if the static chain is there (these are all error conditions). Only a problem on X86. Ciao, Duncan. _______________________________________________ llvm-commits mailing list llvm-commits@cs.uiuc.edu http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
