NFC: refactor replaceDominatedUsesWith

[Prazek]

Summary

Since I will post patch with some changes to
replaceDominatedUsesWith, it would be good to avoid
duplicating code again.

[Prazek]

Add early exit. I also tried to change the iterators for
range, but this would change the behavior (and it would crash)

[davide]

I'm fine with this refactoring, but I'd like to understand what's your long(er) term plan for this first?

[Prazek]

In D32798#745017, @davide wrote:

I'm fine with this refactoring, but I'd like to understand what's your long(er) term plan for this first?

I am not sure how it will go, because I've found the flaw in my idea when writing this. Check out my recent post on mailing list.
Anyway, even if I won't gonna change this code later, I think it make sense to do the refactor.

[davide]

LGTM.

llvm/trunk/lib/Transforms/Utils/Local.cpp

unsigned KnownIDs[] = {
       LLVMContext::MD_noalias,         LLVMContext::MD_range,
       LLVMContext::MD_invariant_load,  LLVMContext::MD_nonnull,
       LLVMContext::MD_invariant_group, LLVMContext::MD_align,
       LLVMContext::MD_dereferenceable,
       LLVMContext::MD_dereferenceable_or_null};
   combineMetadata(K, J, KnownIDs);
 }
 
-unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
-                                        DominatorTree &DT,
-                                        const BasicBlockEdge &Root) {
+template <typename RootType, typename DominatesFn>
+static unsigned replaceDominatedUsesWith(Value *From, Value *To,
+                                         const RootType &Root,
+                                         const DominatesFn &Dominates) {
   assert(From->getType() == To->getType());
-  
   unsigned Count = 0;
   for (Value::use_iterator UI = From->use_begin(), UE = From->use_end();
-       UI != UE; ) {
+       UI != UE;) {
     Use &U = *UI++;
-    if (DT.dominates(Root, U)) {
-      U.set(To);
-      DEBUG(dbgs() << "Replace dominated use of '"
-            << From->getName() << "' as "
+    if (!Dominates(Root, U))
+      continue;
+    DEBUG(dbgs() << "Replace dominated use of '" << From->getName() << "' as "
                  << *To << " in " << *U << "\n");
-      ++Count;
-    }
-  }
   return Count;
 }
 
 unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
                                         DominatorTree &DT,
-                                        const BasicBlock *BB) {
-  assert(From->getType() == To->getType());
-
-  unsigned Count = 0;
-  for (Value::use_iterator UI = From->use_begin(), UE = From->use_end();
-       UI != UE;) {
-    Use &U = *UI++;
-    auto *I = cast<Instruction>(U.getUser());
-    if (DT.properlyDominates(BB, I->getParent())) {
-      U.set(To);
-      DEBUG(dbgs() << "Replace dominated use of '" << From->getName() << "' as "
-                   << *To << " in " << *U << "\n");
-      ++Count;
-    }
-  }
-  return Count;
+                                        const BasicBlockEdge &Root) {
+  auto Dominates = [&DT](const BasicBlockEdge &Root, const Use &U) {
+    return DT.dominates(Root, U);
+  };
+  return ::replaceDominatedUsesWith(From, To, Root, Dominates);
+
+unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
+                                        DominatorTree &DT,
+                                        const BasicBlock *BB) {
+  auto ProperlyDominates = [&DT](const BasicBlock *BB, const Use &U) {
+    auto *I = cast<Instruction>(U.getUser())->getParent();
+    return DT.properlyDominates(BB, I);
+  };
+  return ::replaceDominatedUsesWith(From, To, BB, ProperlyDominates);
 }
 
 bool llvm::callsGCLeafFunction(ImmutableCallSite CS) {
   // Check if the function is specifically marked as a gc leaf function.
   if (CS.hasFnAttr("gc-leaf-function"))
     return true;
   if (const Function *F = CS.getCalledFunction()) {
     if (F->hasFnAttribute("gc-leaf-function"))