[llvm-mca] Add descriptive names for the TimelineView report characters. NFC.

[mattd]

Summary

This change makes the TimelineView source simpler to read and easier to modify in the future.
This patch introduces a class of static chars used as the display values in the TimelineView report, this change just eliminates a few magic characters.

[andreadb]

Thanks Matt,

LGTM

llvm/trunk/tools/llvm-mca/TimelineView.h

void printTimelineViewEntry(llvm::raw_string_ostream &OS,
                               unsigned SourceIndex) const;
   void printWaitTimeEntry(llvm::raw_string_ostream &OS, const WaitTimeEntry &E,
                           unsigned Index) const;
 
   const unsigned DEFAULT_ITERATIONS = 10;
 
   void initialize(unsigned MaxIterations);
 
+  // Display characters for the TimelineView report output.
+  struct DisplayChar {
+    static const char Dispatched = 'D';
+    static const char Executed = 'E';
+    static const char Retired = 'R';
+    static const char Waiting = '='; // Instruction is waiting in the scheduler.
+    static const char Executing = 'e';
+    static const char RetireLag = '-'; // The instruction is waiting to retire.
+  };
+
 public:
   TimelineView(const llvm::MCSubtargetInfo &sti, llvm::MCInstPrinter &Printer,
                const SourceMgr &Sequence, unsigned MaxIterations,
                unsigned Cycles)
       : STI(sti), MCIP(Printer), AsmSequence(Sequence), CurrentCycle(0),
         MaxCycle(Cycles == 0 ? 80 : Cycles), LastCycle(0) {
     initialize(MaxIterations);
   }

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

void TimelineView::printTimelineViewEntry(raw_string_ostream &OS,
                                           const TimelineViewEntry &Entry,
                                           unsigned Iteration,
                                           unsigned SourceIndex) const {
   if (Iteration == 0 && SourceIndex == 0)
     OS << '\n';
   OS << '[' << Iteration << ',' << SourceIndex << "]\t";
   for (unsigned I = 0, E = Entry.CycleDispatched; I < E; ++I)
     OS << ((I % 5 == 0) ? '.' : ' ');
-  OS << 'D';
+  OS << TimelineView::DisplayChar::Dispatched;
   if (Entry.CycleDispatched != Entry.CycleExecuted) {
     // Zero latency instructions have the same value for CycleDispatched,
     // CycleIssued and CycleExecuted.
     for (unsigned I = Entry.CycleDispatched + 1, E = Entry.CycleIssued; I < E;
          ++I)
-      OS << '=';
+      OS << TimelineView::DisplayChar::Waiting;
     if (Entry.CycleIssued == Entry.CycleExecuted)
-      OS << 'E';
+      OS << TimelineView::DisplayChar::DisplayChar::Executed;
     else {
       if (Entry.CycleDispatched != Entry.CycleIssued)
-        OS << 'e';
+        OS << TimelineView::DisplayChar::Executing;
       for (unsigned I = Entry.CycleIssued + 1, E = Entry.CycleExecuted; I < E;
            ++I)
-        OS << 'e';
-      OS << 'E';
+        OS << TimelineView::DisplayChar::Executing;
+      OS << TimelineView::DisplayChar::Executed;
     }
   }
 
   for (unsigned I = Entry.CycleExecuted + 1, E = Entry.CycleRetired; I < E; ++I)
-    OS << '-';
-  OS << 'R';
+    OS << TimelineView::DisplayChar::RetireLag;
+  OS << TimelineView::DisplayChar::Retired;
 
   // Skip other columns.
   for (unsigned I = Entry.CycleRetired + 1, E = LastCycle; I <= E; ++I)
     OS << ((I % 5 == 0 || I == LastCycle) ? '.' : ' ');
 }
 
 static void printTimelineHeader(raw_string_ostream &OS, unsigned Cycles) {
   OS << "\n\nTimeline view:\n";