[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, 10 deletions

diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
index 9178381..dcb4a95 100644
--- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -1435,16 +1435,15 @@ bool JumpThreading::ThreadEdge(BasicBlock *BB,
   for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
     // Scan all uses of this instruction to see if it is used outside of its
     // block, and if so, record them in UsesToRename.
-    for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
-         ++UI) {
-      Instruction *User = cast<Instruction>(*UI);
+    for (Use &U : I->uses()) {
+      Instruction *User = cast<Instruction>(U.getUser());
       if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
-        if (UserPN->getIncomingBlock(UI) == BB)
+        if (UserPN->getIncomingBlock(U) == BB)
           continue;
       } else if (User->getParent() == BB)
         continue;
 
-      UsesToRename.push_back(&UI.getUse());
+      UsesToRename.push_back(&U);
     }
 
     // If there are no uses outside the block, we're done with this instruction.
@@ -1589,16 +1588,15 @@ bool JumpThreading::DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB,
   for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
     // Scan all uses of this instruction to see if it is used outside of its
     // block, and if so, record them in UsesToRename.
-    for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
-         ++UI) {
-      Instruction *User = cast<Instruction>(*UI);
+    for (Use &U : I->uses()) {
+      Instruction *User = cast<Instruction>(U.getUser());
       if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
-        if (UserPN->getIncomingBlock(UI) == BB)
+        if (UserPN->getIncomingBlock(U) == BB)
           continue;
       } else if (User->getParent() == BB)
         continue;
 
-      UsesToRename.push_back(&UI.getUse());
+      UsesToRename.push_back(&U);
     }
 
     // If there are no uses outside the block, we're done with this instruction.