[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, 10 insertions, 12 deletions

diff --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index 1f33557..348e12f 100644
--- a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -657,23 +657,21 @@ bool MemCpyOpt::performCallSlotOptzn(Instruction *cpy,
   // guarantees that it holds only undefined values when passed in (so the final
   // memcpy can be dropped), that it is not read or written between the call and
   // the memcpy, and that writing beyond the end of it is undefined.
-  SmallVector<User*, 8> srcUseList(srcAlloca->use_begin(),
-                                   srcAlloca->use_end());
+  SmallVector<User*, 8> srcUseList(srcAlloca->user_begin(),
+                                   srcAlloca->user_end());
   while (!srcUseList.empty()) {
-    User *UI = srcUseList.pop_back_val();
+    User *U = srcUseList.pop_back_val();
 
-    if (isa<BitCastInst>(UI) || isa<AddrSpaceCastInst>(UI)) {
-      for (User::use_iterator I = UI->use_begin(), E = UI->use_end();
-           I != E; ++I)
-        srcUseList.push_back(*I);
-    } else if (GetElementPtrInst *G = dyn_cast<GetElementPtrInst>(UI)) {
+    if (isa<BitCastInst>(U) || isa<AddrSpaceCastInst>(U)) {
+      for (User *UU : U->users())
+        srcUseList.push_back(UU);
+    } else if (GetElementPtrInst *G = dyn_cast<GetElementPtrInst>(U)) {
       if (G->hasAllZeroIndices())
-        for (User::use_iterator I = UI->use_begin(), E = UI->use_end();
-             I != E; ++I)
-          srcUseList.push_back(*I);
+        for (User *UU : U->users())
+          srcUseList.push_back(UU);
       else
         return false;
-    } else if (UI != C && UI != cpy) {
+    } else if (U != C && U != cpy) {
       return false;
     }
   }