[cfe-commits] [patch] Lookup

[John McCall]

This patch refactors and hopefully simplifies and clarifies some of the 
logic in name lookup, mostly for the benefit of C++.  The major 
structural change is that a LookupResult is now a non-POD type which is 
passed by reference to the lookup routines;  this allows us to eliminate 
a lot of unnecessary copies from C++ lookups that reach into multiple 
scopes.  No allocations or extra logic are required in the common case, 
and along the common C paths, where only a single declaration is found.

In addition, the logic to replace declarations in scope chains is now 
identical to that in declarationReplaces, and we no longer rely on the 
ordering of declarations within a single scope to implement C++ tag-name 
shadowing.

In addition, users which assume that lookup will find at most one 
declaration must now explicitly call either LookupSingleName or, if 
working with a LookupResult, getAsSingleDecl().  These methods exist to 
mark users making this assumption.  Users which for some reason are 
certain that at most one declaration can be returned should use 
getFoundDecl() instead.

My performance evaluations show a (very) small gain on the Cocoa.h 
benchmark.

John.
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