[RISCV] Consistently error for arch strings with trailing _

[asb]

Summary

RISCVISAInfo::parseArchString would sometimes error for arch strings with a trailing _ and sometimes accept them. This patch makes it consistently error.

[craig.topper]

llvm/lib/Support/RISCVISAInfo.cpp

630

Should be use the same "extension name missing after separator '_'" used later?

[asb]

Address review comments.

[craig.topper]

LGTM

llvm/lib/Support/RISCVISAInfo.cpp

RISCVISAInfo::parseArchString(StringRef Arch, bool EnableExperimentalExtension,
   case 'i':
     break;
   case 'g':
     // g = imafd
     StdExts = StdExts.drop_front(4);
     break;
   }
 
+  if (Arch.back() == '_')
+    return createStringError(errc::invalid_argument,
+                             "invalid format - trailing underscore");
+
   // Skip rvxxx
   StringRef Exts = Arch.substr(5);
 
   // Remove multi-letter standard extensions, non-standard extensions and
   // supervisor-level extensions. They have 'z', 'x', 's', 'sx' prefixes.
   // Parse them at the end.
   // Find the very first occurrence of 's', 'x' or 'z'.
   StringRef OtherExts;

llvm/unittests/Support/RISCVISAInfoTest.cpp

for (StringRef Input : {"rv32imafdczifencei", "rv32i_m_a_f_d_c_zifencei"}) {
     EXPECT_EQ(Exts.at("zifencei").ExtName, "zifencei");
   }
 }
 
 TEST(ParseArchString, RejectsDoubleOrTrailingUnderscore) {
   EXPECT_EQ(
       toString(RISCVISAInfo::parseArchString("rv64i__m", true).takeError()),
       "invalid standard user-level extension '_'");
-  EXPECT_EQ(
-      toString(RISCVISAInfo::parseArchString("rv32ezicsr_", true).takeError()),
+  EXPECT_EQ(toString(RISCVISAInfo::parseArchString("rv32ezicsr__zifencei", true)
+                         .takeError()),
             "extension name missing after separator '_'");
 
-  // FIXME: Trailing underscores after single letter extensions are accepted,
-  // which is inconsistent.
-  ASSERT_THAT_EXPECTED(RISCVISAInfo::parseArchString("rv32i_", true),
-                       Succeeded());
-  ASSERT_THAT_EXPECTED(RISCVISAInfo::parseArchString("rv64im_", true),
-                       Succeeded());
+  for (StringRef Input : {"rv32i_", "rv32izicsr_", "rv64im_"}) {
+    EXPECT_EQ(toString(RISCVISAInfo::parseArchString(Input, true).takeError()),
+              "invalid format - trailing underscore");
+  }
 }
 
 TEST(ParseArchString, RejectsDuplicateExtensionNames) {
   EXPECT_EQ(toString(RISCVISAInfo::parseArchString("rv64ii", true).takeError()),
             "invalid standard user-level extension 'i'");
   EXPECT_EQ(toString(RISCVISAInfo::parseArchString("rv32ee", true).takeError()),
             "invalid standard user-level extension 'e'");
   EXPECT_EQ(