[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, 9 insertions, 17 deletions

diff --git a/lib/Transforms/Scalar/StructurizeCFG.cpp b/lib/Transforms/Scalar/StructurizeCFG.cpp
index 8d4aaca8c2..8fd22681e5 100644
--- a/lib/Transforms/Scalar/StructurizeCFG.cpp
+++ b/lib/Transforms/Scalar/StructurizeCFG.cpp
@@ -325,16 +325,10 @@ Value *StructurizeCFG::invert(Value *Condition) {
   if (Instruction *Inst = dyn_cast<Instruction>(Condition)) {
     // Third: Check all the users for an invert
     BasicBlock *Parent = Inst->getParent();
-    for (Value::use_iterator I = Condition->use_begin(),
-           E = Condition->use_end(); I != E; ++I) {
-
-      Instruction *User = dyn_cast<Instruction>(*I);
-      if (!User || User->getParent() != Parent)
-        continue;
-
-      if (match(*I, m_Not(m_Specific(Condition))))
-        return *I;
-    }
+    for (User *U : Condition->users())
+      if (Instruction *I = dyn_cast<Instruction>(U))
+        if (I->getParent() == Parent && match(I, m_Not(m_Specific(Condition))))
+          return I;
 
     // Last option: Create a new instruction
     return BinaryOperator::CreateNot(Condition, "", Parent->getTerminator());
@@ -834,16 +828,14 @@ void StructurizeCFG::rebuildSSA() {
          II != IE; ++II) {
 
       bool Initialized = false;
-      for (Use *I = &II->use_begin().getUse(), *Next; I; I = Next) {
-
-        Next = I->getNext();
-
-        Instruction *User = cast<Instruction>(I->getUser());
+      for (auto I = II->use_begin(), E = II->use_end(); I != E;) {
+        Use &U = *I++;
+        Instruction *User = cast<Instruction>(U.getUser());
         if (User->getParent() == BB) {
           continue;
 
         } else if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
-          if (UserPN->getIncomingBlock(*I) == BB)
+          if (UserPN->getIncomingBlock(U) == BB)
             continue;
         }
 
@@ -857,7 +849,7 @@ void StructurizeCFG::rebuildSSA() {
           Updater.AddAvailableValue(BB, II);
           Initialized = true;
         }
-        Updater.RewriteUseAfterInsertions(*I);
+        Updater.RewriteUseAfterInsertions(U);
       }
     }
 }