[LLVMdev] hash_map issues with Visual Studio

[Morten Ofstad]

I have spent some time examining the llvm code now, and it seems most of 
  the hash_maps are keyed with pointers, and a few with ints. There is 
also one place where the keys are std::string. All these are 
unproblematic with the Visual Studio std_ext::hash_map since it provides 
hash_value functions for all these types (note, it hashes char * as 
pointers, not as strings - but char * is not used as a key anywhere in 
LLVM). This means that although the way of adding your own hashing 
functions is different, the default implementation works for 99% of all 
the cases and the ADT/HashExtras.h file is not necessary.

BUT there is one place where llvm defines it's own hashing function, in 
include/llvm/Target/TargetSchedInfo.h

   template <> struct hash<llvm::OpCodePair> {
     size_t operator()(const llvm::OpCodePair& pair) const {
       return hash<long>()(pair.val);
     }
   };

which for Visual Studio can be replaced with:

     const size_t hash_value(const llvm::OpCodePair& pair) {
       return hash_value((long)pair.val);
     }

however, it seems the OpCodePair class is never used - and specifically 
never used for hash keys. Should this code be deleted? Also, Paolo is 
building LLVM with Visual C, but using a GNU compatible STL. I don't 
know how to detect which of these libraries is used, so it's a bit 
tricky to make sure the right version is compiled.

I would like some input on these issues before submitting a patch. This 
  is the last issue remaining before the core of LLVM compiles 
unmodified with Visual C...

m.