[llvm-mca] Use an ordered map to collect hardware statistics. NFC.

Histogram entries are now ordered by key.  This should improves their
readability when statistics are printed.

llvm-svn: 334961
diff --git a/llvm/tools/llvm-mca/SchedulerStatistics.h b/llvm/tools/llvm-mca/SchedulerStatistics.h
index bbb7535..08d8a34 100644
--- a/llvm/tools/llvm-mca/SchedulerStatistics.h
+++ b/llvm/tools/llvm-mca/SchedulerStatistics.h
@@ -33,15 +33,15 @@
 
 #include "View.h"
 #include "llvm/ADT/SmallVector.h"
-#include "llvm/ADT/DenseMap.h"
 #include "llvm/MC/MCSubtargetInfo.h"
+#include <map>
 
 namespace mca {
 
 class SchedulerStatistics : public View {
   const llvm::MCSchedModel &SM;
 
-  using Histogram = llvm::DenseMap<unsigned, unsigned>;
+  using Histogram = std::map<unsigned, unsigned>;
   Histogram IssuedPerCycle;
 
   unsigned NumIssued;
@@ -53,7 +53,7 @@
     unsigned MaxUsedSlots;
   };
 
-  llvm::DenseMap<unsigned, BufferUsage> BufferedResources;
+  std::map<unsigned, BufferUsage> BufferedResources;
 
   void updateHistograms() {
     IssuedPerCycle[NumIssued]++;