[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

1 files changed, 8 insertions, 12 deletions

diff --git a/llvm/lib/Analysis/CaptureTracking.cpp b/llvm/lib/Analysis/CaptureTracking.cpp
index 6097847..3708e60 100644
--- a/llvm/lib/Analysis/CaptureTracking.cpp
+++ b/llvm/lib/Analysis/CaptureTracking.cpp
@@ -85,17 +85,15 @@ void llvm::PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker) {
   SmallSet<const Use *, Threshold> Visited;
   int Count = 0;
 
-  for (Value::const_use_iterator UI = V->use_begin(), UE = V->use_end();
-       UI != UE; ++UI) {
+  for (const Use &U : V->uses()) {
     // If there are lots of uses, conservatively say that the value
     // is captured to avoid taking too much compile time.
     if (Count++ >= Threshold)
       return Tracker->tooManyUses();
 
-    Use *U = &UI.getUse();
-    if (!Tracker->shouldExplore(U)) continue;
-    Visited.insert(U);
-    Worklist.push_back(U);
+    if (!Tracker->shouldExplore(&U)) continue;
+    Visited.insert(&U);
+    Worklist.push_back(&U);
   }
 
   while (!Worklist.empty()) {
@@ -148,17 +146,15 @@ void llvm::PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker) {
     case Instruction::AddrSpaceCast:
       // The original value is not captured via this if the new value isn't.
       Count = 0;
-      for (Instruction::use_iterator UI = I->use_begin(), UE = I->use_end();
-           UI != UE; ++UI) {
+      for (Use &UU : I->uses()) {
         // If there are lots of uses, conservatively say that the value
         // is captured to avoid taking too much compile time.
         if (Count++ >= Threshold)
           return Tracker->tooManyUses();
 
-        Use *U = &UI.getUse();
-        if (Visited.insert(U))
-          if (Tracker->shouldExplore(U))
-            Worklist.push_back(U);
+        if (Visited.insert(&UU))
+          if (Tracker->shouldExplore(&UU))
+            Worklist.push_back(&UU);
       }
       break;
     case Instruction::ICmp: