[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. =]

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203364 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Bitcode/Reader/BitcodeReader.cpp

@@ -332,7 +332,7 @@ void BitcodeReaderValueList::ResolveConstantForwardRefs() {
     // new value.  If they reference more than one placeholder, update them all
     // at once.
     while (!Placeholder->use_empty()) {
-      Value::use_iterator UI = Placeholder->use_begin();
+      auto UI = Placeholder->user_begin();
       User *U = *UI;
 
       // If the using object isn't uniqued, just update the operands.  This
@@ -3116,8 +3116,8 @@ error_code BitcodeReader::Materialize(GlobalValue *GV) {
   for (UpgradedIntrinsicMap::iterator I = UpgradedIntrinsics.begin(),
        E = UpgradedIntrinsics.end(); I != E; ++I) {
     if (I->first != I->second) {
-      for (Value::use_iterator UI = I->first->use_begin(),
-           UE = I->first->use_end(); UI != UE; ) {
+      for (auto UI = I->first->user_begin(), UE = I->first->user_end();
+           UI != UE;) {
         if (CallInst* CI = dyn_cast<CallInst>(*UI++))
           UpgradeIntrinsicCall(CI, I->second);
       }
@@ -3172,8 +3172,8 @@ error_code BitcodeReader::MaterializeModule(Module *M) {
   for (std::vector<std::pair<Function*, Function*> >::iterator I =
        UpgradedIntrinsics.begin(), E = UpgradedIntrinsics.end(); I != E; ++I) {
     if (I->first != I->second) {
-      for (Value::use_iterator UI = I->first->use_begin(),
-           UE = I->first->use_end(); UI != UE; ) {
+      for (auto UI = I->first->user_begin(), UE = I->first->user_end();
+           UI != UE;) {
         if (CallInst* CI = dyn_cast<CallInst>(*UI++))
           UpgradeIntrinsicCall(CI, I->second);
       }

lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -1807,17 +1807,10 @@ static void WriteUseList(const Value *V, const ValueEnumerator &VE,
     return;
 
   // Make a copy of the in-memory use-list for sorting.
-  unsigned UseListSize = std::distance(V->use_begin(), V->use_end());
-  SmallVector<const User*, 8> UseList;
-  UseList.reserve(UseListSize);
-  for (Value::const_use_iterator I = V->use_begin(), E = V->use_end();
-       I != E; ++I) {
-    const User *U = *I;
-    UseList.push_back(U);
-  }
+  SmallVector<const User*, 8> UserList(V->user_begin(), V->user_end());
 
   // Sort the copy based on the order read by the BitcodeReader.
-  std::sort(UseList.begin(), UseList.end(), bitcodereader_order);
+  std::sort(UserList.begin(), UserList.end(), bitcodereader_order);
 
   // TODO: Generate a diff between the BitcodeWriter in-memory use-list and the
   // sorted list (i.e., the expected BitcodeReader in-memory use-list).

lib/Bitcode/Writer/ValueEnumerator.cpp

@@ -159,12 +159,11 @@ void ValueEnumerator::print(raw_ostream &OS, const ValueMapType &Map,
     V->dump();
 
     OS << " Uses(" << std::distance(V->use_begin(),V->use_end()) << "):";
-    for (Value::const_use_iterator UI = V->use_begin(), UE = V->use_end();
-         UI != UE; ++UI) {
-      if (UI != V->use_begin())
+    for (const Use &U : V->uses()) {
+      if (&U != &*V->use_begin())
         OS << ",";
-      if((*UI)->hasName())
-        OS << " " << (*UI)->getName();
+      if(U->hasName())
+        OS << " " << U->getName();
       else
         OS << " [null]";