get the first few tags from a precomputed table (count can be increased if desired)

llvm-svn: 108549

llvm/lib/VMCore/Use.cpp

@@ -86,6 +86,15 @@ const Use *Use::getImpliedUser() const {
 //===----------------------------------------------------------------------===//
 
 Use *Use::initTags(Use * const Start, Use *Stop, ptrdiff_t Done) {
+  while (Done < 6) {
+    if (Start == Stop--)
+      return Start;
+    static const PrevPtrTag tags[6] = { fullStopTag, oneDigitTag, stopTag,
+                                        oneDigitTag, oneDigitTag, stopTag };
+    Stop->Prev.setFromOpaqueValue(reinterpret_cast<Use**>(tags[Done++]));
+    Stop->Val = 0;
+  }
+
   ptrdiff_t Count = Done;
   while (Start != Stop) {
     --Stop;