1. Use llvm::lower_bound to find the feature from Feature array 2. Check feature dependency when disable extension 3. Delete todo

llvm/lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp

else
                    "remove extension or reset features");
 
     Parser.Lex();
 
     if (Parser.getTok().isNot(AsmToken::Identifier))
       return Error(Parser.getTok().getLoc(),
                    "unexpected token, expected identifier");
 
-    StringRef Extension = Parser.getTok().getString();
+    StringRef ExtStr = Parser.getTok().getString();
 
-    // TODO: Enable or disable extension according to extension and extension
-    // version number. Currently extension version number is not supported.
-    if (Extension.find_if(isDigit) != StringRef::npos)
+    if (ExtStr.find_if(isDigit) != StringRef::npos)
       return Error(Parser.getTok().getLoc(),
-                   "extension version number is not yet supported");
+                   "Don't specify version number, extensions don't rely on "
+                   "version numbers");
+
+    ArrayRef<SubtargetFeatureKV> KVArray(RISCVFeatureKV);
+    auto Ext = llvm::lower_bound(KVArray, ExtStr);
+    if (Ext == KVArray.end() || StringRef(Ext->Key) != ExtStr)
+      return Error(Parser.getTok().getLoc(), "unknown extension");
 
-    for (auto Feature : RISCVFeatureKV) {
-      if (Extension == Feature.Key) {
-        if (IsAdd) {
-          setFeatureBits(Feature.Value, Feature.Key);
-          getTargetStreamer().emitDirectiveOptionArchPlus(Extension);
-        } else {
-          clearFeatureBits(Feature.Value, Feature.Key);
-          getTargetStreamer().emitDirectiveOptionArchMinus(Extension);
-        }
-        Parser.Lex();
-        return Parser.parseToken(AsmToken::EndOfStatement,
-                                 "unexpected token, expected end of statement");
-      }
-    }
-    return Error(Parser.getTok().getLoc(), "unknown extension");
-  }
+      setFeatureBits(Ext->Value, Ext->Key);
+      getTargetStreamer().emitDirectiveOptionArchPlus(Ext->Key);
+      // Check dependency. It is invalid to disable an extension that
+      // there are other enabled extensions depend on it.
+      for (auto Feature : KVArray) {
+        if (getSTI().hasFeature(Feature.Value) &&
+            Feature.Implies.test(Ext->Value))
+          return Error(Parser.getTok().getLoc(),
+                       Twine("Can't disable ") + Ext->Key + " extension, " +
+                           Feature.Key + " extension requires " + Ext->Key +
+                           " extension be enabled");
+
+      clearFeatureBits(Ext->Value, Ext->Key);
+      getTargetStreamer().emitDirectiveOptionArchMinus(Ext->Key);
+    }
+
 
   if (Option == "rvc") {
     getTargetStreamer().emitDirectiveOptionRVC();
 
     Parser.Lex();
     if (Parser.getTok().isNot(AsmToken::EndOfStatement))
       return Error(Parser.getTok().getLoc(),
                    "unexpected token, expected end of statement");

llvm/lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.cpp

 void RISCVTargetAsmStreamer::emitIntTextAttribute(unsigned Attribute,
                                                   unsigned IntValue,
                                                   StringRef StringValue) {}
 
 void RISCVTargetAsmStreamer::emitDirectiveOptionArchEqual(StringRef Value) {
   OS << "\t .option\tarch,\t=" << Value << "\"\n";
 }
 void RISCVTargetAsmStreamer::emitDirectiveOptionArchPlus(StringRef Value) {
-  OS << "\t .option\tarch,\t+" << Value << "\"\n";
+  OS << "\t .option\tarch,\t+" << Value << "\n";
 }
 void RISCVTargetAsmStreamer::emitDirectiveOptionArchMinus(StringRef Value) {
-  OS << "\t .option\tarch,\t-" << Value << "\"\n";
+  OS << "\t .option\tarch,\t-" << Value << "\n";
 }
 
 void RISCVTargetAsmStreamer::finishAttributeSection() {}

llvm/test/MC/RISCV/option-invalid.s

 .option arch, +x
 
 # CHECK: error: unexpected token, expected end of statement
 .option arch, =rv32i foo
 
 # CHECK: error: unexpected token, expected end of statement
 .option arch, +c foo
 
-# CHECK: error: extension version number is not yet supported
+# CHECK: error: Don't specify version number, extensions don't rely on version numbers
 .option arch, +c2p0
 
+.option arch, +d
+# CHECK: error: Can't disable f extension, d extension requires f extension be enabled
+.option arch, -f
+
 # CHECK: error: unexpected token, expected end of statement
 .option rvc foo
 
 # CHECK: warning: unknown option, expected 'push', 'pop', 'rvc', 'norvc', 'arch', 'relax' or 'norelax'
 .option bar
 
 # CHECK: error: .option pop with no .option push
 .option pop
 
 # CHECK: error: unexpected token, expected end of statement
 .option push 123
 
 # CHECK: error: unexpected token, expected end of statement
 .option pop 123
+