[AST] Move a function definition into the cpp [NFC]

llvm-svn: 340382
diff --git a/llvm/lib/Analysis/AliasSetTracker.cpp b/llvm/lib/Analysis/AliasSetTracker.cpp
index dc6ecd5..66fdf7f 100644
--- a/llvm/lib/Analysis/AliasSetTracker.cpp
+++ b/llvm/lib/Analysis/AliasSetTracker.cpp
@@ -252,6 +252,18 @@
   return false;
 }
 
+Instruction* AliasSet::getUniqueInstruction() {
+  if (size() != 0)
+    // Can't track source of pointer, might be many instruction
+    return nullptr;
+  if (AliasAny)
+    // May have collapses alias set
+    return nullptr;
+ if (1 != UnknownInsts.size())
+    return nullptr;
+  return cast<Instruction>(UnknownInsts[0]);
+}
+
 void AliasSetTracker::clear() {
   // Delete all the PointerRec entries.
   for (PointerMapType::iterator I = PointerMap.begin(), E = PointerMap.end();