[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, 11 insertions, 14 deletions

diff --git a/lib/Transforms/Scalar/LoopUnswitch.cpp b/lib/Transforms/Scalar/LoopUnswitch.cpp
index 61de996cff..5954f4af51 100644
--- a/lib/Transforms/Scalar/LoopUnswitch.cpp
+++ b/lib/Transforms/Scalar/LoopUnswitch.cpp
@@ -939,9 +939,8 @@ static void ReplaceUsesOfWith(Instruction *I, Value *V,
       Worklist.push_back(Use);
 
   // Add users to the worklist which may be simplified now.
-  for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
-       UI != E; ++UI)
-    Worklist.push_back(cast<Instruction>(*UI));
+  for (User *U : I->users())
+    Worklist.push_back(cast<Instruction>(U));
   LPM->deleteSimpleAnalysisValue(I, L);
   RemoveFromWorklist(I, Worklist);
   I->replaceAllUsesWith(V);
@@ -991,12 +990,11 @@ void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
       Replacement = ConstantInt::get(Type::getInt1Ty(Val->getContext()),
                                      !cast<ConstantInt>(Val)->getZExtValue());
 
-    for (Value::use_iterator UI = LIC->use_begin(), E = LIC->use_end();
-         UI != E; ++UI) {
-      Instruction *U = dyn_cast<Instruction>(*UI);
-      if (!U || !L->contains(U))
+    for (User *U : LIC->users()) {
+      Instruction *UI = dyn_cast<Instruction>(U);
+      if (!UI || !L->contains(UI))
         continue;
-      Worklist.push_back(U);
+      Worklist.push_back(UI);
     }
 
     for (std::vector<Instruction*>::iterator UI = Worklist.begin(),
@@ -1010,19 +1008,18 @@ void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
   // Otherwise, we don't know the precise value of LIC, but we do know that it
   // is certainly NOT "Val".  As such, simplify any uses in the loop that we
   // can.  This case occurs when we unswitch switch statements.
-  for (Value::use_iterator UI = LIC->use_begin(), E = LIC->use_end();
-       UI != E; ++UI) {
-    Instruction *U = dyn_cast<Instruction>(*UI);
-    if (!U || !L->contains(U))
+  for (User *U : LIC->users()) {
+    Instruction *UI = dyn_cast<Instruction>(U);
+    if (!UI || !L->contains(UI))
       continue;
 
-    Worklist.push_back(U);
+    Worklist.push_back(UI);
 
     // TODO: We could do other simplifications, for example, turning
     // 'icmp eq LIC, Val' -> false.
 
     // If we know that LIC is not Val, use this info to simplify code.
-    SwitchInst *SI = dyn_cast<SwitchInst>(U);
+    SwitchInst *SI = dyn_cast<SwitchInst>(UI);
     if (SI == 0 || !isa<ConstantInt>(Val)) continue;
 
     SwitchInst::CaseIt DeadCase = SI->findCaseValue(cast<ConstantInt>(Val));