Cleanup collectChangingRegs

The handling of the epilogue is best expressed as an early exit and
there is no reason to look for register defs in DbgValue MIs.

Patch by Frederic Riss!

llvm-svn: 214986
diff --git a/llvm/lib/CodeGen/AsmPrinter/DbgValueHistoryCalculator.cpp b/llvm/lib/CodeGen/AsmPrinter/DbgValueHistoryCalculator.cpp
index f557ccd..143b013 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DbgValueHistoryCalculator.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DbgValueHistoryCalculator.cpp
@@ -152,10 +152,11 @@
                                 std::set<unsigned> &Regs) {
   for (const auto &MBB : *MF) {
     auto FirstEpilogueInst = getFirstEpilogueInst(MBB);
-    bool IsInEpilogue = false;
+
     for (const auto &MI : MBB) {
-      IsInEpilogue |= &MI == FirstEpilogueInst;
-      if (!MI.getFlag(MachineInstr::FrameSetup) && !IsInEpilogue)
+      if (&MI == FirstEpilogueInst)
+        break;
+      if (!MI.getFlag(MachineInstr::FrameSetup))
         collectClobberedRegisters(MI, TRI, Regs);
     }
   }