Make this pr obey menable-experimental-extensions.

Author: Yeting Kuo

clang/lib/Driver/ToolChains/Clang.cpp

@@ -8449,6 +8449,11 @@ void ClangAs::AddRISCVTargetArgs(const ArgList &Args,
       CmdArgs.push_back("-mllvm");
       CmdArgs.push_back("-riscv-add-build-attributes");
   }
+
+  if (!Args.hasArg(options::OPT_menable_experimental_extensions)) {
+    CmdArgs.push_back("-mllvm");
+    CmdArgs.push_back("-riscv-disable-experimental-ext");
+  }
 }
 
 void ClangAs::ConstructJob(Compilation &C, const JobAction &JA,

clang/test/Driver/riscv-option-arch.s

@@ -0,0 +1,5 @@
+# RUN: %clang --target=riscv64 -menable-experimental-extensions -c -o /dev/null %s
+# RUN: ! %clang --target=riscv64 -c -o /dev/null %s 2>&1 | FileCheck -check-prefixes=CHECK-ERR %s
+
+.option arch, +zicfiss
+# CHECK-ERR: Unexpected experimental extensions.

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

@@ -51,6 +51,9 @@ STATISTIC(RISCVNumInstrsCompressed,
 
 static cl::opt<bool> AddBuildAttributes("riscv-add-build-attributes",
                                         cl::init(false));
+static cl::opt<bool>
+    DisableExperimentalExtension("riscv-disable-experimental-ext",
+                                 cl::init(false));
 
 namespace llvm {
 extern const SubtargetFeatureKV RISCVFeatureKV[RISCV::NumSubtargetFeatures];
@@ -2825,6 +2828,9 @@ bool RISCVAsmParser::parseDirectiveOption() {
       }
 
       std::string &&Feature = RISCVISAInfo::getTargetFeatureForExtension(Arch);
+      if (DisableExperimentalExtension &&
+          StringRef(Feature).starts_with("experimental-"))
+        return Error(Loc, "Unexpected experimental extensions.");
       auto Ext = llvm::lower_bound(RISCVFeatureKV, Feature);
       if (Ext == std::end(RISCVFeatureKV) || StringRef(Ext->Key) != Feature ||
           !RISCVISAInfo::isSupportedExtension(Arch)) {