[llvm-exegesis][NFC] Use an enum instead of a string for benchmark mode.

Summary: YAML encoding is backwards-compatible.

Reviewers: gchatelet

Subscribers: tschuett, llvm-commits

Differential Revision: https://reviews.llvm.org/D47705

llvm-svn: 333886
diff --git a/llvm/tools/llvm-exegesis/lib/Uops.cpp b/llvm/tools/llvm-exegesis/lib/Uops.cpp
index 9428286..145bfad 100644
--- a/llvm/tools/llvm-exegesis/lib/Uops.cpp
+++ b/llvm/tools/llvm-exegesis/lib/Uops.cpp
@@ -141,7 +141,9 @@
 
 UopsBenchmarkRunner::~UopsBenchmarkRunner() = default;
 
-const char *UopsBenchmarkRunner::getDisplayName() const { return "uops"; }
+InstructionBenchmarkKey::ModeE UopsBenchmarkRunner::getMode() const {
+  return InstructionBenchmarkKey::Uops;
+}
 
 llvm::Expected<std::vector<llvm::MCInst>>
 UopsBenchmarkRunner::createSnippet(RegisterAliasingTrackerCache &RATC,