[RISCV] Reject 'g' with explicit version in parseArchString

[asb]

Summary

There is no versioning scheme for the 'g' shorthand for imafd (or in current ISA specs, imafd_zifencei_zicsr). As such, the only sensible behaviour to me seems to be to reject a version for it.

[craig.topper]

Makes sense to me.

[kito-cheng]

LGTM, the version scheme of g already broken for a while.

llvm/lib/Support/RISCVISAInfo.cpp

if (HasRV64)
           errc::invalid_argument,
           "standard user-level extension 'e' requires 'rv32'");
     break;
   }
   case 'i':
     break;
   case 'g':
     // g = imafd
+    if (Arch.size() > 5 && isdigit(Arch[5]))
+      return createStringError(errc::invalid_argument,
+                               "version not supported for 'g'");
     StdExts = StdExts.drop_front(4);
     break;
   }
 
   // Skip rvxxx
   StringRef Exts = Arch.substr(5);
 
   // Remove multi-letter standard extensions, non-standard extensions and

llvm/unittests/Support/RISCVISAInfoTest.cpp

 TEST(ParseArchString, RejectsUnrecognizedVersionForExperimentalExtension) {
   EXPECT_EQ(
       toString(
           RISCVISAInfo::parseArchString("rv64izihintntl9p9", true).takeError()),
       "unsupported version number 9.9 for experimental extension 'zihintntl' "
       "(this compiler supports 0.2)");
 }
 
-TEST(ParseArchString, AcceptsExtensionVersionForG) {
-  // FIXME: As there is no versioning scheme for G, arguably an error should
-  // be produced.
-  auto MaybeISAInfo = RISCVISAInfo::parseArchString("rv64g9p9", true, false);
-  ASSERT_THAT_EXPECTED(MaybeISAInfo, Succeeded());
-  RISCVISAInfo::OrderedExtensionMap Exts = (*MaybeISAInfo)->getExtensions();
-  EXPECT_EQ(Exts.size(), 5UL);
-  EXPECT_TRUE(Exts.at("i") == (RISCVExtensionInfo{"i", 2, 0}));
+TEST(ParseArchString, RejectsExtensionVersionForG) {
+  for (StringRef Input : {"rv32g1c", "rv64g2p0"}) {
+    EXPECT_EQ(toString(RISCVISAInfo::parseArchString(Input, true).takeError()),
+              "version not supported for 'g'");
+  }
 }
 
 TEST(ParseArchString, AddsImpliedExtensions) {
   // Does not attempt to exhaustively test all implications.
   auto MaybeRV64ID = RISCVISAInfo::parseArchString("rv64id", true);
   ASSERT_THAT_EXPECTED(MaybeRV64ID, Succeeded());
   RISCVISAInfo::OrderedExtensionMap ExtsRV64ID =
       (*MaybeRV64ID)->getExtensions();