[llvm-mca][timeline] Indicate output was stopped due to cycle limit.

[dsanders]

Summary

It can be a bit confusing to stop with no explanation so we should indicate
when further output was prevented by the cycle limit.

[andreadb]

LGTM. Thanks!

llvm/tools/llvm-mca/Views/TimelineView.cpp

for (const MCInst &Inst : Source) {
       const TimelineViewEntry &Entry = Timeline[IID];
       // When an instruction is retired after timeline-max-cycles,
       // its CycleRetired is left at 0. However, it's possible for
       // a 0 latency instruction to be retired during cycle 0 and we
       // don't want to early exit in that case. The CycleExecuted
       // attribute is set correctly whether or not it is greater
       // than timeline-max-cycles so we can use that to ensure
       // we don't early exit because of a 0 latency instruction.
-      if (Entry.CycleRetired == 0 && Entry.CycleExecuted != 0)
+      if (Entry.CycleRetired == 0 && Entry.CycleExecuted != 0) {
+        FOS << "Truncated display due to cycle limit\n";
         return;
+      }
 
       unsigned SourceIndex = IID % Source.size();
       printTimelineViewEntry(FOS, Entry, Iteration, SourceIndex);
       FOS << "   " << printInstructionString(Inst) << '\n';
       FOS.flush();
 
       ++IID;
     }