[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

3 files changed, 17 insertions, 26 deletions

diff --git a/lib/Transforms/ObjCARC/ObjCARCContract.cpp b/lib/Transforms/ObjCARC/ObjCARCContract.cpp
index b1dc2ec533..1412181766 100644
--- a/lib/Transforms/ObjCARC/ObjCARCContract.cpp
+++ b/lib/Transforms/ObjCARC/ObjCARCContract.cpp
@@ -440,17 +440,17 @@ bool ObjCARCContract::runOnFunction(Function &F) {
 
     // Don't use GetObjCArg because we don't want to look through bitcasts
     // and such; to do the replacement, the argument must have type i8*.
-    const Value *Arg = cast<CallInst>(Inst)->getArgOperand(0);
+    Value *Arg = cast<CallInst>(Inst)->getArgOperand(0);
     for (;;) {
       // If we're compiling bugpointed code, don't get in trouble.
       if (!isa<Instruction>(Arg) && !isa<Argument>(Arg))
         break;
       // Look through the uses of the pointer.
-      for (Value::const_use_iterator UI = Arg->use_begin(), UE = Arg->use_end();
+      for (Value::use_iterator UI = Arg->use_begin(), UE = Arg->use_end();
            UI != UE; ) {
-        Use &U = UI.getUse();
-        unsigned OperandNo = UI.getOperandNo();
-        ++UI; // Increment UI now, because we may unlink its element.
+        // Increment UI now, because we may unlink its element.
+        Use &U = *UI++;
+        unsigned OperandNo = U.getOperandNo();
 
         // If the call's return value dominates a use of the call's argument
         // value, rewrite the use to use the return value. We check for
@@ -476,8 +476,7 @@ bool ObjCARCContract::runOnFunction(Function &F) {
               if (PHI->getIncomingBlock(i) == BB) {
                 // Keep the UI iterator valid.
                 if (&PHI->getOperandUse(
-                      PHINode::getOperandNumForIncomingValue(i)) ==
-                    &UI.getUse())
+                        PHINode::getOperandNumForIncomingValue(i)) == &U)
                   ++UI;
                 PHI->setIncomingValue(i, Replacement);
               }
diff --git a/lib/Transforms/ObjCARC/ObjCARCOpts.cpp b/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
index 4e2cf59d18..eed3cb23ca 100644
--- a/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
+++ b/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
@@ -163,12 +163,9 @@ static const Value *FindSingleUseIdentifiedObject(const Value *Arg) {
   // If we found an identifiable object but it has multiple uses, but they are
   // trivial uses, we can still consider this to be a single-use value.
   if (IsObjCIdentifiedObject(Arg)) {
-    for (Value::const_use_iterator UI = Arg->use_begin(), UE = Arg->use_end();
-         UI != UE; ++UI) {
-      const User *U = *UI;
+    for (const User *U : Arg->users())
       if (!U->use_empty() || StripPointerCastsAndObjCCalls(U) != Arg)
          return 0;
-    }
 
     return Arg;
   }
@@ -1266,13 +1263,11 @@ ObjCARCOpt::OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV,
   Users.push_back(Ptr);
   do {
     Ptr = Users.pop_back_val();
-    for (Value::const_use_iterator UI = Ptr->use_begin(), UE = Ptr->use_end();
-         UI != UE; ++UI) {
-      const User *I = *UI;
-      if (isa<ReturnInst>(I) || GetBasicInstructionClass(I) == IC_RetainRV)
+    for (const User *U : Ptr->users()) {
+      if (isa<ReturnInst>(U) || GetBasicInstructionClass(U) == IC_RetainRV)
         return;
-      if (isa<BitCastInst>(I))
-        Users.push_back(I);
+      if (isa<BitCastInst>(U))
+        Users.push_back(U);
     }
   } while (!Users.empty());
 
@@ -2787,9 +2782,8 @@ void ObjCARCOpt::OptimizeWeakCalls(Function &F) {
     CallInst *Call = cast<CallInst>(Inst);
     Value *Arg = Call->getArgOperand(0);
     if (AllocaInst *Alloca = dyn_cast<AllocaInst>(Arg)) {
-      for (Value::use_iterator UI = Alloca->use_begin(),
-           UE = Alloca->use_end(); UI != UE; ++UI) {
-        const Instruction *UserInst = cast<Instruction>(*UI);
+      for (User *U : Alloca->users()) {
+        const Instruction *UserInst = cast<Instruction>(U);
         switch (GetBasicInstructionClass(UserInst)) {
         case IC_InitWeak:
         case IC_StoreWeak:
@@ -2800,8 +2794,7 @@ void ObjCARCOpt::OptimizeWeakCalls(Function &F) {
         }
       }
       Changed = true;
-      for (Value::use_iterator UI = Alloca->use_begin(),
-           UE = Alloca->use_end(); UI != UE; ) {
+      for (auto UI = Alloca->user_begin(), UE = Alloca->user_end(); UI != UE;) {
         CallInst *UserInst = cast<CallInst>(*UI++);
         switch (GetBasicInstructionClass(UserInst)) {
         case IC_InitWeak:
diff --git a/lib/Transforms/ObjCARC/ProvenanceAnalysis.cpp b/lib/Transforms/ObjCARC/ProvenanceAnalysis.cpp
index ae3c6282cf..22be6fdf45 100644
--- a/lib/Transforms/ObjCARC/ProvenanceAnalysis.cpp
+++ b/lib/Transforms/ObjCARC/ProvenanceAnalysis.cpp
@@ -79,11 +79,10 @@ static bool IsStoredObjCPointer(const Value *P) {
   Visited.insert(P);
   do {
     P = Worklist.pop_back_val();
-    for (Value::const_use_iterator UI = P->use_begin(), UE = P->use_end();
-         UI != UE; ++UI) {
-      const User *Ur = *UI;
+    for (const Use &U : P->uses()) {
+      const User *Ur = U.getUser();
       if (isa<StoreInst>(Ur)) {
-        if (UI.getOperandNo() == 0)
+        if (U.getOperandNo() == 0)
           // The pointer is stored.
           return true;
         // The pointed is stored through.