[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

1 files changed, 8 insertions, 9 deletions

diff --git a/lib/Transforms/Utils/LCSSA.cpp b/lib/Transforms/Utils/LCSSA.cpp
index 18717de6ae..d5381753a2 100644
--- a/lib/Transforms/Utils/LCSSA.cpp
+++ b/lib/Transforms/Utils/LCSSA.cpp
@@ -65,15 +65,14 @@ static bool processInstruction(Loop &L, Instruction &Inst, DominatorTree &DT,
 
   BasicBlock *InstBB = Inst.getParent();
 
-  for (Value::use_iterator UI = Inst.use_begin(), E = Inst.use_end(); UI != E;
-       ++UI) {
-    User *U = *UI;
-    BasicBlock *UserBB = cast<Instruction>(U)->getParent();
-    if (PHINode *PN = dyn_cast<PHINode>(U))
-      UserBB = PN->getIncomingBlock(UI);
+  for (Use &U : Inst.uses()) {
+    Instruction *User = cast<Instruction>(U.getUser());
+    BasicBlock *UserBB = User->getParent();
+    if (PHINode *PN = dyn_cast<PHINode>(User))
+      UserBB = PN->getIncomingBlock(U);
 
     if (InstBB != UserBB && !L.contains(UserBB))
-      UsesToRewrite.push_back(&UI.getUse());
+      UsesToRewrite.push_back(&U);
   }
 
   // If there are no uses outside the loop, exit with no change.
@@ -208,8 +207,8 @@ bool llvm::formLCSSA(Loop &L, DominatorTree &DT, ScalarEvolution *SE) {
       // Reject two common cases fast: instructions with no uses (like stores)
       // and instructions with one use that is in the same block as this.
       if (I->use_empty() ||
-          (I->hasOneUse() && I->use_back()->getParent() == BB &&
-           !isa<PHINode>(I->use_back())))
+          (I->hasOneUse() && I->user_back()->getParent() == BB &&
+           !isa<PHINode>(I->user_back())))
         continue;
 
       Changed |= processInstruction(L, *I, DT, ExitBlocks, PredCache);