[AArch64] Add support for the 'R' architecture profile.

This change introduces subtarget features to predicate certain
instructions and system registers that are available only on
'A' profile targets. Those features are not present when
targeting a generic CPU, which is the default processor.

In other words the generic CPU now means the intersection of
'A' and 'R' profiles. To maintain backwards compatibility we
enable the features that correspond to -march=armv8-a when the
architecture is not explicitly specified on the command line.

References: https://developer.arm.com/documentation/ddi0600/latest

Differential Revision: https://reviews.llvm.org/D110065

Author: labrinea

clang/lib/Basic/Targets/AArch64.cpp

@@ -51,6 +51,15 @@ static StringRef getArchVersionString(llvm::AArch64::ArchKind Kind) {
   }
 }
 
+StringRef AArch64TargetInfo::getArchProfile() const {
+  switch (ArchKind) {
+  case llvm::AArch64::ArchKind::ARMV8R:
+    return "R";
+  default:
+    return "A";
+  }
+}
+
 AArch64TargetInfo::AArch64TargetInfo(const llvm::Triple &Triple,
                                      const TargetOptions &Opts)
     : TargetInfo(Triple), ABI("aapcs") {
@@ -257,7 +266,7 @@ void AArch64TargetInfo::getTargetDefines(const LangOptions &Opts,
   // ACLE predefines. Many can only have one possible value on v8 AArch64.
   Builder.defineMacro("__ARM_ACLE", "200");
   Builder.defineMacro("__ARM_ARCH", getArchVersionString(ArchKind));
-  Builder.defineMacro("__ARM_ARCH_PROFILE", "'A'");
+  Builder.defineMacro("__ARM_ARCH_PROFILE", "'" + getArchProfile() + "'");
 
   Builder.defineMacro("__ARM_64BIT_STATE", "1");
   Builder.defineMacro("__ARM_PCS_AAPCS64", "1");
@@ -511,7 +520,7 @@ bool AArch64TargetInfo::handleTargetFeatures(std::vector<std::string> &Features,
   HasMatmulFP32 = false;
   HasLSE = false;
 
-  ArchKind = llvm::AArch64::ArchKind::ARMV8A;
+  ArchKind = llvm::AArch64::ArchKind::INVALID;
 
   for (const auto &Feature : Features) {
     if (Feature == "+neon")
@@ -573,6 +582,8 @@ bool AArch64TargetInfo::handleTargetFeatures(std::vector<std::string> &Features,
       HasSM4 = true;
     if (Feature == "+strict-align")
       HasUnaligned = false;
+    if (Feature == "+v8a")
+      ArchKind = llvm::AArch64::ArchKind::ARMV8A;
     if (Feature == "+v8.1a")
       ArchKind = llvm::AArch64::ArchKind::ARMV8_1A;
     if (Feature == "+v8.2a")

clang/lib/Basic/Targets/AArch64.h

@@ -59,6 +59,7 @@ class LLVM_LIBRARY_VISIBILITY AArch64TargetInfo : public TargetInfo {
   static const Builtin::Info BuiltinInfo[];
 
   std::string ABI;
+  StringRef getArchProfile() const;
 
 public:
   AArch64TargetInfo(const llvm::Triple &Triple, const TargetOptions &Opts);