[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, 6 insertions, 7 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 61b121816e4..8c0ad525980 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -1937,16 +1937,15 @@ static Instruction *ProcessUGT_ADDCST_ADD(ICmpInst &I, Value *A, Value *B,
   // and truncates that discard the high bits of the add.  Verify that this is
   // the case.
   Instruction *OrigAdd = cast<Instruction>(AddWithCst->getOperand(0));
-  for (Value::use_iterator UI = OrigAdd->use_begin(), E = OrigAdd->use_end();
-       UI != E; ++UI) {
-    if (*UI == AddWithCst) continue;
+  for (User *U : OrigAdd->users()) {
+    if (U == AddWithCst) continue;
 
     // Only accept truncates for now.  We would really like a nice recursive
     // predicate like SimplifyDemandedBits, but which goes downwards the use-def
     // chain to see which bits of a value are actually demanded.  If the
     // original add had another add which was then immediately truncated, we
     // could still do the transformation.
-    TruncInst *TI = dyn_cast<TruncInst>(*UI);
+    TruncInst *TI = dyn_cast<TruncInst>(U);
     if (TI == 0 ||
         TI->getType()->getPrimitiveSizeInBits() > NewWidth) return 0;
   }
@@ -2068,8 +2067,8 @@ static bool swapMayExposeCSEOpportunities(const Value * Op0,
   // At the end, if the benefit is greater than 0, Op0 should come second to
   // expose more CSE opportunities.
   int GlobalSwapBenefits = 0;
-  for (Value::const_use_iterator UI = Op0->use_begin(), UIEnd = Op0->use_end(); UI != UIEnd; ++UI) {
-    const BinaryOperator *BinOp = dyn_cast<BinaryOperator>(*UI);
+  for (const User *U : Op0->users()) {
+    const BinaryOperator *BinOp = dyn_cast<BinaryOperator>(U);
     if (!BinOp || BinOp->getOpcode() != Instruction::Sub)
       continue;
     // If Op0 is the first argument, this is not beneficial to swap the
@@ -2468,7 +2467,7 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
   // operands has at least one user besides the compare (the select),
   // which would often largely negate the benefit of folding anyway.
   if (I.hasOneUse())
-    if (SelectInst *SI = dyn_cast<SelectInst>(*I.use_begin()))
+    if (SelectInst *SI = dyn_cast<SelectInst>(*I.user_begin()))
       if ((SI->getOperand(1) == Op0 && SI->getOperand(2) == Op1) ||
           (SI->getOperand(2) == Op0 && SI->getOperand(1) == Op1))
         return 0;