[RISCV][Clang][TargetParser] Support getting feature unaligned-scalar-mem from mcpu. (#71513)

This patch reference ac1ffd3 to suppot
a soft coding way to identify whether a cpu has a feature
`unaligned-scalar-mem` by `RISCVProcessors.td`.
This patch does not provide test case since there is no risc-v cpu
support `unaligned-scalar-mem` in llvm upstream now.

Author: yetingk

clang/lib/Driver/ToolChains/Arch/RISCV.cpp

@@ -63,6 +63,9 @@ static void getRISCFeaturesFromMcpu(const Driver &D, const Arg *A,
       D.Diag(clang::diag::err_drv_unsupported_option_argument)
           << A->getSpelling() << Mcpu;
   }
+
+  if (llvm::RISCV::hasFastUnalignedAccess(Mcpu))
+    Features.push_back("+unaligned-scalar-mem");
 }
 
 void riscv::getRISCVTargetFeatures(const Driver &D, const llvm::Triple &Triple,

llvm/include/llvm/TargetParser/RISCVTargetParser.h

@@ -31,6 +31,7 @@ bool parseTuneCPU(StringRef CPU, bool IsRV64);
 StringRef getMArchFromMcpu(StringRef CPU);
 void fillValidCPUArchList(SmallVectorImpl<StringRef> &Values, bool IsRV64);
 void fillValidTuneCPUArchList(SmallVectorImpl<StringRef> &Values, bool IsRV64);
+bool hasFastUnalignedAccess(StringRef CPU);
 
 } // namespace RISCV
 } // namespace llvm

llvm/lib/TargetParser/RISCVTargetParser.cpp

@@ -20,20 +20,21 @@ namespace llvm {
 namespace RISCV {
 
 enum CPUKind : unsigned {
-#define PROC(ENUM, NAME, DEFAULT_MARCH) CK_##ENUM,
+#define PROC(ENUM, NAME, DEFAULT_MARCH, FAST_UNALIGN) CK_##ENUM,
 #define TUNE_PROC(ENUM, NAME) CK_##ENUM,
 #include "llvm/TargetParser/RISCVTargetParserDef.inc"
 };
 
 struct CPUInfo {
   StringLiteral Name;
   StringLiteral DefaultMarch;
+  bool FastUnalignedAccess;
   bool is64Bit() const { return DefaultMarch.starts_with("rv64"); }
 };
 
 constexpr CPUInfo RISCVCPUInfo[] = {
-#define PROC(ENUM, NAME, DEFAULT_MARCH)                              \
-  {NAME, DEFAULT_MARCH},
+#define PROC(ENUM, NAME, DEFAULT_MARCH, FAST_UNALIGN)                          \
+  {NAME, DEFAULT_MARCH, FAST_UNALIGN},
 #include "llvm/TargetParser/RISCVTargetParserDef.inc"
 };
 
@@ -44,6 +45,11 @@ static const CPUInfo *getCPUInfoByName(StringRef CPU) {
   return nullptr;
 }
 
+bool hasFastUnalignedAccess(StringRef CPU) {
+  const CPUInfo *Info = getCPUInfoByName(CPU);
+  return Info && Info->FastUnalignedAccess;
+}
+
 bool parseCPU(StringRef CPU, bool IsRV64) {
   const CPUInfo *Info = getCPUInfoByName(CPU);
 

llvm/utils/TableGen/RISCVTargetDefEmitter.cpp

@@ -49,7 +49,7 @@ static std::string getMArch(const Record &Rec) {
 
 static void EmitRISCVTargetDef(RecordKeeper &RK, raw_ostream &OS) {
   OS << "#ifndef PROC\n"
-     << "#define PROC(ENUM, NAME, DEFAULT_MARCH)\n"
+     << "#define PROC(ENUM, NAME, DEFAULT_MARCH, FAST_UNALIGNED_ACCESS)\n"
      << "#endif\n\n";
 
   // Iterate on all definition records.
@@ -60,9 +60,14 @@ static void EmitRISCVTargetDef(RecordKeeper &RK, raw_ostream &OS) {
     if (MArch.empty())
       MArch = getMArch(*Rec);
 
+    const bool FastUnalignedAccess =
+        any_of(Rec->getValueAsListOfDefs("Features"), [&](auto &Feature) {
+          return Feature->getValueAsString("Name") == "unaligned-scalar-mem";
+        });
+
     OS << "PROC(" << Rec->getName() << ", "
        << "{\"" << Rec->getValueAsString("Name") << "\"}, "
-       << "{\"" << MArch << "\"})\n";
+       << "{\"" << MArch << "\"}, " << FastUnalignedAccess << ")\n";
   }
   OS << "\n#undef PROC\n";
   OS << "\n";