[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, 3 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
index 9089372dfef..521dc9cd2eb 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -118,7 +118,7 @@ Instruction *InstCombiner::scalarizePHI(ExtractElementInst &EI, PHINode *PN) {
   // If so, it's known at this point that one operand is PHI and the other is
   // an extractelement node. Find the PHI user that is not the extractelement
   // node.
-  Value::use_iterator iu = PN->use_begin();
+  auto iu = PN->user_begin();
   Instruction *PHIUser = dyn_cast<Instruction>(*iu);
   if (PHIUser == cast<Instruction>(&EI))
     PHIUser = cast<Instruction>(*(++iu));
@@ -126,7 +126,7 @@ Instruction *InstCombiner::scalarizePHI(ExtractElementInst &EI, PHINode *PN) {
   // Verify that this PHI user has one use, which is the PHI itself,
   // and that it is a binary operation which is cheap to scalarize.
   // otherwise return NULL.
-  if (!PHIUser->hasOneUse() || !(PHIUser->use_back() == PN) ||
+  if (!PHIUser->hasOneUse() || !(PHIUser->user_back() == PN) ||
       !(isa<BinaryOperator>(PHIUser)) || !CheapToScalarize(PHIUser, true))
     return NULL;
 
@@ -521,7 +521,7 @@ Instruction *InstCombiner::visitInsertElementInst(InsertElementInst &IE) {
 
       // If this insertelement isn't used by some other insertelement, turn it
       // (and any insertelements it points to), into one big shuffle.
-      if (!IE.hasOneUse() || !isa<InsertElementInst>(IE.use_back())) {
+      if (!IE.hasOneUse() || !isa<InsertElementInst>(IE.user_back())) {
         SmallVector<Constant*, 16> Mask;
         ShuffleOps LR = CollectShuffleElements(&IE, Mask, 0);