hacking clang IdentifierTable

Hi all,

Clang use a hash table to store all its identifiers. The hash table definition is:

typedef llvm::StringMap<IdentifierInfo*, llvm::BumpPtrAllocator> HashTableTy;
HashTableTy HashTable;

Can anyone explain the mechnism of handling the name string key collision for me? Is there a IdentifierInfo objects chain or list for
variable or function with the same name?

Thanks very much!


This hash table is just used to unique IdentifierInfos. IdentifierInfo itself holds a client-specific pointer of storage; Sema uses that pointer to hold either a NamedDecl* or an IdDeclInfo*, which we distinguish with the usual low-bit tagging trick. IdDeclInfo is basically a SmallVector<NamedDecl*,2>. There's some extra magic to make macros/PCH not require redundant hashes, but that's the basic idea.

Anyway, this is all sufficient to implement unqualified lookup in C and Objective C, but our C++ implementation can only get away with relying on IdentifierInfo when looking in a function; we have to fall back on DeclContext lookups (i.e. rehashing the string in different hash tables) when looking into pretty much any other kind of scope.


Queries about Clang should be sent to clang-dev, not llvm-dev.