[RISCV] Teach .option arch to support experimental extensions. (#89727)

Previously `.option arch` denied extenions are not belongs to RISC-V
features. But experimental features have experimental- prefix, so
`.option arch` can not serve for experimental extension.
This patch uses the features of extensions to identify extension
existance.

Author: yetingk

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

@@ -0,0 +1,7 @@
+// 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
+
+void foo() {
+  asm volatile (".option arch, +zicfiss");
+  // CHECK-ERR: Unexpected experimental extensions.
+}

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

@@ -84,6 +84,9 @@ class RISCVAsmParser : public MCTargetAsmParser {
   SMLoc getLoc() const { return getParser().getTok().getLoc(); }
   bool isRV64() const { return getSTI().hasFeature(RISCV::Feature64Bit); }
   bool isRVE() const { return getSTI().hasFeature(RISCV::FeatureStdExtE); }
+  bool enableExperimentalExtension() const {
+    return getSTI().hasFeature(RISCV::Experimental);
+  }
 
   RISCVTargetStreamer &getTargetStreamer() {
     assert(getParser().getStreamer().getTargetStreamer() &&
@@ -2824,17 +2827,19 @@ bool RISCVAsmParser::parseDirectiveOption() {
         break;
       }
 
-      auto Ext = llvm::lower_bound(RISCVFeatureKV, Arch);
-      if (Ext == std::end(RISCVFeatureKV) || StringRef(Ext->Key) != Arch ||
-          !RISCVISAInfo::isSupportedExtension(Arch)) {
-        if (isDigit(Arch.back()))
-          return Error(
-              Loc,
-              "Extension version number parsing not currently implemented");
+      if (isDigit(Arch.back()))
+        return Error(
+            Loc, "Extension version number parsing not currently implemented");
+
+      std::string Feature = RISCVISAInfo::getTargetFeatureForExtension(Arch);
+      if (!enableExperimentalExtension() &&
+          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)
         return Error(Loc, "unknown extension feature");
-      }
 
-      Args.emplace_back(Type, Ext->Key);
+      Args.emplace_back(Type, Arch.str());
 
       if (Type == RISCVOptionArchArgType::Plus) {
         FeatureBitset OldFeatureBits = STI->getFeatureBits();

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

@@ -1,7 +1,7 @@
-# RUN: llvm-mc -triple riscv32 -show-encoding < %s \
+# RUN: llvm-mc -triple riscv32 -mattr=+experimental -show-encoding < %s \
 # RUN:   | FileCheck -check-prefixes=CHECK %s
-# RUN: llvm-mc -triple riscv32 -filetype=obj < %s \
-# RUN:   | llvm-objdump  --triple=riscv32 --mattr=+c,+m,+a,+f,+zba -d -M no-aliases - \
+# RUN: llvm-mc -triple riscv32 -mattr=+experimental -filetype=obj < %s \
+# RUN:   | llvm-objdump  --triple=riscv32 --mattr=+c,+m,+a,+f,+zba,+experimental-zicfiss -d -M no-aliases - \
 # RUN:   | FileCheck -check-prefixes=CHECK-INST %s
 
 # Test '.option arch, +' and '.option arch, -' directive
@@ -78,6 +78,13 @@ lr.w t0, (t1)
 # CHECK: encoding: [0xb3,0x22,0x73,0x20]
 sh1add t0, t1, t2
 
+# Test experimental extension
+# CHECK: .option arch, +zicfiss
+.option arch, +zicfiss
+# CHECK-INST: sspopchk ra
+# CHECK: encoding: [0x73,0xc0,0xc0,0xcd]
+sspopchk ra
+
 # Test '.option arch, <arch-string>' directive
 # CHECK: .option arch, rv32i2p1_m2p0_a2p1_c2p0
 .option arch, rv32i2p1_m2p0_a2p1_c2p0