[C++11] Add range based accessors for the Use-Def chain of a Value.

This requires a number of steps.
1) Move value_use_iterator into the Value class as an implementation
   detail
2) Change it to actually be a *Use* iterator rather than a *User*
   iterator.
3) Add an adaptor which is a User iterator that always looks through the
   Use to the User.
4) Wrap these in Value::use_iterator and Value::user_iterator typedefs.
5) Add the range adaptors as Value::uses() and Value::users().
6) Update *all* of the callers to correctly distinguish between whether
   they wanted a use_iterator (and to explicitly dig out the User when
   needed), or a user_iterator which makes the Use itself totally
   opaque.

Because #6 requires churning essentially everything that walked the
Use-Def chains, I went ahead and added all of the range adaptors and
switched them to range-based loops where appropriate. Also because the
renaming requires at least churning every line of code, it didn't make
any sense to split these up into multiple commits -- all of which would
touch all of the same lies of code.

The result is still not quite optimal. The Value::use_iterator is a nice
regular iterator, but Value::user_iterator is an iterator over User*s
rather than over the User objects themselves. As a consequence, it fits
a bit awkwardly into the range-based world and it has the weird
extra-dereferencing 'operator->' that so many of our iterators have.
I think this could be fixed by providing something which transforms
a range of T&s into a range of T*s, but that *can* be separated into
another patch, and it isn't yet 100% clear whether this is the right
move.

However, this change gets us most of the benefit and cleans up
a substantial amount of code around Use and User. =]

llvm-svn: 203364
diff --git a/llvm/lib/Transforms/Utils/CodeExtractor.cpp b/llvm/lib/Transforms/Utils/CodeExtractor.cpp
index c96c030..b814842 100644
--- a/llvm/lib/Transforms/Utils/CodeExtractor.cpp
+++ b/llvm/lib/Transforms/Utils/CodeExtractor.cpp
@@ -171,9 +171,8 @@
         if (definedInCaller(Blocks, *OI))
           Inputs.insert(*OI);
 
-      for (Value::use_iterator UI = II->use_begin(), UE = II->use_end();
-           UI != UE; ++UI)
-        if (!definedInRegion(Blocks, *UI)) {
+      for (User *U : II->users())
+        if (!definedInRegion(Blocks, U)) {
           Outputs.insert(II);
           break;
         }
@@ -369,7 +368,7 @@
     } else
       RewriteVal = AI++;
 
-    std::vector<User*> Users(inputs[i]->use_begin(), inputs[i]->use_end());
+    std::vector<User*> Users(inputs[i]->user_begin(), inputs[i]->user_end());
     for (std::vector<User*>::iterator use = Users.begin(), useE = Users.end();
          use != useE; ++use)
       if (Instruction* inst = dyn_cast<Instruction>(*use))
@@ -389,7 +388,7 @@
   // Rewrite branches to basic blocks outside of the loop to new dummy blocks
   // within the new function. This must be done before we lose track of which
   // blocks were originally in the code region.
-  std::vector<User*> Users(header->use_begin(), header->use_end());
+  std::vector<User*> Users(header->user_begin(), header->user_end());
   for (unsigned i = 0, e = Users.size(); i != e; ++i)
     // The BasicBlock which contains the branch is not in the region
     // modify the branch target to a new block
@@ -405,13 +404,12 @@
 /// that uses the value within the basic block, and return the predecessor
 /// block associated with that use, or return 0 if none is found.
 static BasicBlock* FindPhiPredForUseInBlock(Value* Used, BasicBlock* BB) {
-  for (Value::use_iterator UI = Used->use_begin(),
-       UE = Used->use_end(); UI != UE; ++UI) {
-     PHINode *P = dyn_cast<PHINode>(*UI);
+  for (Use &U : Used->uses()) {
+     PHINode *P = dyn_cast<PHINode>(U.getUser());
      if (P && P->getParent() == BB)
-       return P->getIncomingBlock(UI);
+       return P->getIncomingBlock(U);
   }
-  
+
   return 0;
 }
 
@@ -502,7 +500,7 @@
     LoadInst *load = new LoadInst(Output, outputs[i]->getName()+".reload");
     Reloads.push_back(load);
     codeReplacer->getInstList().push_back(load);
-    std::vector<User*> Users(outputs[i]->use_begin(), outputs[i]->use_end());
+    std::vector<User*> Users(outputs[i]->user_begin(), outputs[i]->user_end());
     for (unsigned u = 0, e = Users.size(); u != e; ++u) {
       Instruction *inst = cast<Instruction>(Users[u]);
       if (!Blocks.count(inst->getParent()))