Fix some nasty callgraph dangling pointer problems in

argpromotion and structretpromote.  Basically, when replacing
a function, they used the 'changeFunction' api which changes
the entry in the function map (and steals/reuses the callgraph
node).

This has some interesting effects: first, the problem is that it doesn't
update the "callee" edges in any callees of the function in the call graph.
Second, this covers for a major problem in all the CGSCC pass stuff, which 
is that it is completely broken when functions are deleted if they *don't*
reuse a CGN.  (there is a cute little fixme about this though :).

This patch changes the protocol that CGSCC passes must obey: now the CGSCC 
pass manager copies the SCC and preincrements its iterator to avoid passes
invalidating it.  This allows CGSCC passes to mutate the current SCC.  However
multiple passes may be run on that SCC, so if passes do this, they are now
required to *update* the SCC to be current when they return.

Other less interesting parts of this patch are that it makes passes update
the CG more directly, eliminates changeFunction, and requires clients of
replaceCallSite to specify the new callee CGN if they are changing it.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@80527 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CallGraphSCCPass.h

@@ -46,7 +46,10 @@ struct CallGraphSCCPass : public Pass {
   /// non-recursive (or only self-recursive) functions will have an SCC size of
   /// 1, where recursive portions of the call graph will have SCC size > 1.
   ///
-  virtual bool runOnSCC(const std::vector<CallGraphNode *> &SCC) = 0;
+  /// SCC passes that add or delete functions to the SCC are required to update
+  /// the SCC list, otherwise stale pointers may be dereferenced.
+  ///
+  virtual bool runOnSCC(std::vector<CallGraphNode *> &SCC) = 0;
 
   /// doFinalization - This method is called after the SCC's of the program has
   /// been processed, allowing the pass to do final cleanup as necessary.