[AST] Reorder code to reduce a future patch diff [NFC]

llvm-svn: 340383
diff --git a/llvm/lib/Analysis/AliasSetTracker.cpp b/llvm/lib/Analysis/AliasSetTracker.cpp
index 66fdf7f..a9b01df 100644
--- a/llvm/lib/Analysis/AliasSetTracker.cpp
+++ b/llvm/lib/Analysis/AliasSetTracker.cpp
@@ -253,12 +253,12 @@
 }
 
 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 (size() != 0)
+    // Can't track source of pointer, might be many instruction
+    return nullptr;
  if (1 != UnknownInsts.size())
     return nullptr;
   return cast<Instruction>(UnknownInsts[0]);