[clang] [llvm] [NFC] [RISCV] Refactor class RISCVExtension (PR #120040)

[Pengcheng Wang via llvm-commits]

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@@ -12,21 +12,32 @@
 
 // Subclass of SubtargetFeature to be used when the feature is also a RISC-V
 // extension. Extensions have a version and may be experimental.
+// NOTE: The extension name must start with
+//       - "FeatureStdExt" for standard extensions
+//       - "FeatureVendor" for vendor-specific extensions
 //
-// name      - Name of the extension in lower case.
 // major     - Major version of extension.
 // minor     - Minor version of extension.
-// desc      - Description of extension.
 // implies   - Extensions or features implied by this extension.
 // fieldname - name of field to create in RISCVSubtarget. By default replaces
 //             uses the record name by replacing Feature with Has.
 // value     - Value to assign to the field in RISCVSubtarget when this
 //             extension is enabled. Usually "true", but can be changed.
-class RISCVExtension<string name, int major, int minor, string desc,
+// IsExperimental
+//           - Indicates whether the extension is experimental
+class RISCVExtension<int major, int minor, string desc,
                      list<SubtargetFeature> implies = [],
                      string fieldname = !subst("Feature", "Has", NAME),
-                     string value = "true">
-    : SubtargetFeature<name, fieldname, value, desc, implies> {
+                     string value = "true", bit IsExperimental = false>
+    : SubtargetFeature<"", fieldname, value, "", implies> {
+  defvar N = !subst("FeatureVendor", "", !subst("FeatureStdExt", "", NAME));
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wangpc-pp wrote:

Use a meaningful variable name like `extName` (we tend to use lowerCamelCase for local variables in TableGen)?

https://github.com/llvm/llvm-project/pull/120040