[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, 2 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Scalar/ConstantProp.cpp b/llvm/lib/Transforms/Scalar/ConstantProp.cpp
index 7625ad64b4a..7045b365c21 100644
--- a/llvm/lib/Transforms/Scalar/ConstantProp.cpp
+++ b/llvm/lib/Transforms/Scalar/ConstantProp.cpp
@@ -79,9 +79,8 @@ bool ConstantPropagation::runOnFunction(Function &F) {
       if (Constant *C = ConstantFoldInstruction(I, DL, TLI)) {
         // Add all of the users of this instruction to the worklist, they might
         // be constant propagatable now...
-        for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
-             UI != UE; ++UI)
-          WorkList.insert(cast<Instruction>(*UI));
+        for (User *U : I->users())
+          WorkList.insert(cast<Instruction>(U));
 
         // Replace all of the uses of a variable with uses of the constant.
         I->replaceAllUsesWith(C);