[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, 11 insertions, 12 deletions

diff --git a/llvm/lib/Transforms/IPO/IPConstantPropagation.cpp b/llvm/lib/Transforms/IPO/IPConstantPropagation.cpp
index 1e5974c935a..8684796b4e7 100644
--- a/llvm/lib/Transforms/IPO/IPConstantPropagation.cpp
+++ b/llvm/lib/Transforms/IPO/IPConstantPropagation.cpp
@@ -86,18 +86,18 @@ bool IPCP::PropagateConstantsIntoArguments(Function &F) {
   ArgumentConstants.resize(F.arg_size());
 
   unsigned NumNonconstant = 0;
-  for (Value::use_iterator UI = F.use_begin(), E = F.use_end(); UI != E; ++UI) {
-    User *U = *UI;
+  for (Use &U : F.uses()) {
+    User *UR = U.getUser();
     // Ignore blockaddress uses.
-    if (isa<BlockAddress>(U)) continue;
+    if (isa<BlockAddress>(UR)) continue;
     
     // Used by a non-instruction, or not the callee of a function, do not
     // transform.
-    if (!isa<CallInst>(U) && !isa<InvokeInst>(U))
+    if (!isa<CallInst>(UR) && !isa<InvokeInst>(UR))
       return false;
     
-    CallSite CS(cast<Instruction>(U));
-    if (!CS.isCallee(UI))
+    CallSite CS(cast<Instruction>(UR));
+    if (!CS.isCallee(&U))
       return false;
 
     // Check out all of the potentially constant arguments.  Note that we don't
@@ -220,13 +220,13 @@ bool IPCP::PropagateConstantReturn(Function &F) {
   // over all users, replacing any uses of the return value with the returned
   // constant.
   bool MadeChange = false;
-  for (Value::use_iterator UI = F.use_begin(), E = F.use_end(); UI != E; ++UI) {
-    CallSite CS(*UI);
+  for (Use &U : F.uses()) {
+    CallSite CS(U.getUser());
     Instruction* Call = CS.getInstruction();
 
     // Not a call instruction or a call instruction that's not calling F
     // directly?
-    if (!Call || !CS.isCallee(UI))
+    if (!Call || !CS.isCallee(&U))
       continue;
     
     // Call result not used?
@@ -244,9 +244,8 @@ bool IPCP::PropagateConstantReturn(Function &F) {
       Call->replaceAllUsesWith(New);
       continue;
     }
-   
-    for (Value::use_iterator I = Call->use_begin(), E = Call->use_end();
-         I != E;) {
+
+    for (auto I = Call->user_begin(), E = Call->user_end(); I != E;) {
       Instruction *Ins = cast<Instruction>(*I);
 
       // Increment now, so we can remove the use