[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, 11 insertions, 15 deletions

diff --git a/llvm/lib/Transforms/IPO/MergeFunctions.cpp b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
index 0ab1c76..64f6377 100644
--- a/llvm/lib/Transforms/IPO/MergeFunctions.cpp
+++ b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
@@ -697,14 +697,13 @@ bool DenseMapInfo<ComparableFunction>::isEqual(const ComparableFunction &LHS,
 // Replace direct callers of Old with New.
 void MergeFunctions::replaceDirectCallers(Function *Old, Function *New) {
   Constant *BitcastNew = ConstantExpr::getBitCast(New, Old->getType());
-  for (Value::use_iterator UI = Old->use_begin(), UE = Old->use_end();
-       UI != UE;) {
-    Value::use_iterator TheIter = UI;
+  for (auto UI = Old->use_begin(), UE = Old->use_end(); UI != UE;) {
+    Use *U = &*UI;
     ++UI;
-    CallSite CS(*TheIter);
-    if (CS && CS.isCallee(TheIter)) {
+    CallSite CS(U->getUser());
+    if (CS && CS.isCallee(U)) {
       remove(CS.getInstruction()->getParent()->getParent());
-      TheIter.getUse().set(BitcastNew);
+      U->set(BitcastNew);
     }
   }
 }
@@ -895,17 +894,14 @@ void MergeFunctions::removeUsers(Value *V) {
     Value *V = Worklist.back();
     Worklist.pop_back();
 
-    for (Value::use_iterator UI = V->use_begin(), UE = V->use_end();
-         UI != UE; ++UI) {
-      Use &U = UI.getUse();
-      if (Instruction *I = dyn_cast<Instruction>(U.getUser())) {
+    for (User *U : V->users()) {
+      if (Instruction *I = dyn_cast<Instruction>(U)) {
         remove(I->getParent()->getParent());
-      } else if (isa<GlobalValue>(U.getUser())) {
+      } else if (isa<GlobalValue>(U)) {
         // do nothing
-      } else if (Constant *C = dyn_cast<Constant>(U.getUser())) {
-        for (Value::use_iterator CUI = C->use_begin(), CUE = C->use_end();
-             CUI != CUE; ++CUI)
-          Worklist.push_back(*CUI);
+      } else if (Constant *C = dyn_cast<Constant>(U)) {
+        for (User *UU : C->users())
+          Worklist.push_back(UU);
       }
     }
   }