[llvm-mca] Simplify the logic in FetchStage. NFCI

Only method 'getNextInstruction()' needs to interact with the SourceMgr.

llvm-svn: 345185
diff --git a/llvm/tools/llvm-mca/lib/Pipeline.cpp b/llvm/tools/llvm-mca/lib/Pipeline.cpp
index 2d9aa6b..ad49522 100644
--- a/llvm/tools/llvm-mca/lib/Pipeline.cpp
+++ b/llvm/tools/llvm-mca/lib/Pipeline.cpp
@@ -39,13 +39,14 @@
 Error Pipeline::run() {
   assert(!Stages.empty() && "Unexpected empty pipeline found!");
 
-  while (hasWorkToProcess()) {
+  do {
     notifyCycleBegin();
     if (Error Err = runCycle())
       return Err;
     notifyCycleEnd();
     ++Cycles;
-  }
+  } while (hasWorkToProcess());
+
   return ErrorSuccess();
 }