[RISCV] Allow Zicsr/Zifencei to duplicate with g (#136842)

This matches GCC and we supported it in LLVM 17/18.

Fixes #136803

(cherry picked from commit 6c3373534305a2ce23dd939344dd0a387a09fe88)

clang/docs/ReleaseNotes.rst

@@ -1267,6 +1267,8 @@ RISC-V Support
 - The option ``-mcmodel=large`` for the large code model is supported.
 - Bump RVV intrinsic to version 1.0, the spec: https://github.com/riscv-non-isa/rvv-intrinsic-doc/releases/tag/v1.0.0-rc4
 
+- `Zicsr` / `Zifencei` are allowed to be duplicated in the presence of `g` in `-march`.
+
 CUDA/HIP Language Changes
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 - Fixed a bug about overriding a constexpr pure-virtual member function with a non-constexpr virtual member function which causes compilation failure when including standard C++ header `format`.

llvm/lib/TargetParser/RISCVISAInfo.cpp

@@ -45,9 +45,8 @@ struct RISCVProfile {
 
 } // end anonymous namespace
 
-static const char *RISCVGImplications[] = {
-  "i", "m", "a", "f", "d", "zicsr", "zifencei"
-};
+static const char *RISCVGImplications[] = {"i", "m", "a", "f", "d"};
+static const char *RISCVGImplicationsZi[] = {"zicsr", "zifencei"};
 
 #define GET_SUPPORTED_EXTENSIONS
 #include "llvm/TargetParser/RISCVTargetParserDef.inc"
@@ -718,6 +717,19 @@ RISCVISAInfo::parseArchString(StringRef Arch, bool EnableExperimentalExtension,
     } while (!Ext.empty());
   }
 
+  // We add Zicsr/Zifenci as final to allow duplicated "zicsr"/"zifencei" like
+  // "rv64g_zicsr_zifencei".
+  if (Baseline == 'g') {
+    for (const char *Ext : RISCVGImplicationsZi) {
+      if (ISAInfo->Exts.count(Ext))
+        continue;
+
+      auto Version = findDefaultVersion(Ext);
+      assert(Version && "Default extension version not found?");
+      ISAInfo->Exts[std::string(Ext)] = {Version->Major, Version->Minor};
+    }
+  }
+
   return RISCVISAInfo::postProcessAndChecking(std::move(ISAInfo));
 }
 

llvm/unittests/TargetParser/RISCVISAInfoTest.cpp

@@ -507,6 +507,14 @@ TEST(ParseArchString, RejectsDoubleOrTrailingUnderscore) {
 }
 
 TEST(ParseArchString, RejectsDuplicateExtensionNames) {
+  // Zicsr/Zifencei are allowed to duplicate with "g".
+  ASSERT_THAT_EXPECTED(RISCVISAInfo::parseArchString("rv64g_zicsr", true),
+                       Succeeded());
+  ASSERT_THAT_EXPECTED(RISCVISAInfo::parseArchString("rv64g_zifencei", true),
+                       Succeeded());
+  ASSERT_THAT_EXPECTED(
+      RISCVISAInfo::parseArchString("rv64g_zicsr_zifencei", true), Succeeded());
+
   EXPECT_EQ(toString(RISCVISAInfo::parseArchString("rv64ii", true).takeError()),
             "invalid standard user-level extension 'i'");
   EXPECT_EQ(toString(RISCVISAInfo::parseArchString("rv32ee", true).takeError()),