[RISCV] Use hasFeature instead of checkFeature in llvm-exegesis. NFC

Until recently checkFeature was quite slow. llvm#130936

I was curious where we use checkFeature and noticed these. I thought
we could use hasFeature instead of going through strings.

Author: topperc

llvm/tools/llvm-exegesis/lib/RISCV/Target.cpp

@@ -156,15 +156,33 @@ template <class BaseT> class RISCVSnippetGenerator : public BaseT {
     // FIXME: We could have obtained these two constants from RISCVSubtarget
     // but in order to get that from TargetMachine, we need a Function.
     const MCSubtargetInfo &STI = State.getSubtargetInfo();
-    ELEN = STI.checkFeatures("+zve64x") ? 64 : 32;
-
-    std::string ZvlQuery;
-    for (unsigned Size = 32; Size <= 65536; Size *= 2) {
-      ZvlQuery = "+zvl";
-      raw_string_ostream SS(ZvlQuery);
-      SS << Size << "b";
-      if (STI.checkFeatures(SS.str()) && ZvlVLen < Size)
-        ZvlVLen = Size;
+    ELEN = STI.hasFeature(RISCV::FeatureStdExtZve64x) ? 64 : 32;
+
+    static_assert(RISCV::FeatureStdExtZvl64b == RISCV::FeatureStdExtZvl32b + 1);
+    static_assert(RISCV::FeatureStdExtZvl128b ==
+                  RISCV::FeatureStdExtZvl32b + 2);
+    static_assert(RISCV::FeatureStdExtZvl256b ==
+                  RISCV::FeatureStdExtZvl32b + 3);
+    static_assert(RISCV::FeatureStdExtZvl512b ==
+                  RISCV::FeatureStdExtZvl32b + 4);
+    static_assert(RISCV::FeatureStdExtZvl1024b ==
+                  RISCV::FeatureStdExtZvl32b + 5);
+    static_assert(RISCV::FeatureStdExtZvl2048b ==
+                  RISCV::FeatureStdExtZvl32b + 6);
+    static_assert(RISCV::FeatureStdExtZvl4096b ==
+                  RISCV::FeatureStdExtZvl32b + 7);
+    static_assert(RISCV::FeatureStdExtZvl8192b ==
+                  RISCV::FeatureStdExtZvl32b + 8);
+    static_assert(RISCV::FeatureStdExtZvl16384b ==
+                  RISCV::FeatureStdExtZvl32b + 9);
+    static_assert(RISCV::FeatureStdExtZvl32768b ==
+                  RISCV::FeatureStdExtZvl32b + 10);
+    static_assert(RISCV::FeatureStdExtZvl65536b ==
+                  RISCV::FeatureStdExtZvl32b + 11);
+    for (unsigned Feature = RISCV::FeatureStdExtZvl32b, Size = 32;
+         Size <= 65536; ++Feature, Size *= 2) {
+      if (STI.hasFeature(Feature))
+        ZvlVLen = std::max(ZvlVLen, Size);
     }
   }