[AArch64][TargetParser] Move extension aliases into tablegen (llvm#91970)

Author: tmatheson-arm

llvm/include/llvm/TargetParser/AArch64TargetParser.h

@@ -114,11 +114,12 @@ using ExtensionBitset = Bitset<AEK_NUM_EXTENSIONS>;
 // SubtargetFeature which may represent either an actual extension or some
 // internal LLVM property.
 struct ExtensionInfo {
-  StringRef Name;              // Human readable name, e.g. "profile".
-  ArchExtKind ID;              // Corresponding to the ArchExtKind, this
-                               // extensions representation in the bitfield.
-  StringRef Feature;           // -mattr enable string, e.g. "+spe"
-  StringRef NegFeature;        // -mattr disable string, e.g. "-spe"
+  StringRef Name;                 // Human readable name, e.g. "profile".
+  std::optional<StringRef> Alias; // An alias for this extension, if one exists.
+  ArchExtKind ID;                 // Corresponding to the ArchExtKind, this
+                                  // extensions representation in the bitfield.
+  StringRef Feature;              // -mattr enable string, e.g. "+spe"
+  StringRef NegFeature;           // -mattr disable string, e.g. "-spe"
   CPUFeatures CPUFeature;      // Function Multi Versioning (FMV) bitfield value
                                // set in __aarch64_cpu_features
   StringRef DependentFeatures; // FMV enabled features string,
@@ -674,8 +675,6 @@ struct Alias {
 inline constexpr Alias CpuAliases[] = {{"cobalt-100", "neoverse-n2"},
                                        {"grace", "neoverse-v2"}};
 
-inline constexpr Alias ExtAliases[] = {{"rdma", "rdm"}};
-
 const ExtensionInfo &getExtensionByID(ArchExtKind(ExtID));
 
 bool getExtensionFeatures(
@@ -684,7 +683,6 @@ bool getExtensionFeatures(
 
 StringRef getArchExtFeature(StringRef ArchExt);
 StringRef resolveCPUAlias(StringRef CPU);
-StringRef resolveExtAlias(StringRef ArchExt);
 
 // Information by Name
 const ArchInfo *getArchForCpu(StringRef CPU);

llvm/lib/Target/AArch64/AArch64Features.td

@@ -39,6 +39,10 @@ class Extension<
     // not doing so.
     string MArchName = TargetFeatureName;
 
+    // An alias that can be used on the command line, if the extension has one.
+    // Used for correcting historical names while remaining backwards compatible.
+    string MArchAlias = "";
+
     // Function MultiVersioning (FMV) properties
 
     // A C++ expression giving the number of the bit in the FMV ABI.
@@ -163,6 +167,7 @@ def FeatureOutlineAtomics : SubtargetFeature<"outline-atomics", "OutlineAtomics"
 def FeatureFMV : SubtargetFeature<"fmv", "HasFMV", "true",
   "Enable Function Multi Versioning support.">;
 
+let MArchAlias = "rdma" in
 def FeatureRDM : Extension<"rdm", "RDM",
   "Enable ARMv8.1 Rounding Double Multiply Add/Subtract instructions (FEAT_RDM)",
   [FeatureNEON],

llvm/lib/TargetParser/AArch64TargetParser.cpp

@@ -74,13 +74,6 @@ StringRef AArch64::resolveCPUAlias(StringRef Name) {
   return Name;
 }
 
-StringRef AArch64::resolveExtAlias(StringRef Name) {
-  for (const auto &A : ExtAliases)
-    if (A.AltName == Name)
-      return A.Name;
-  return Name;
-}
-
 StringRef AArch64::getArchExtFeature(StringRef ArchExt) {
   bool IsNegated = ArchExt.starts_with("no");
   StringRef ArchExtBase = IsNegated ? ArchExt.drop_front(2) : ArchExt;
@@ -120,13 +113,10 @@ const AArch64::ArchInfo *AArch64::parseArch(StringRef Arch) {
   return {};
 }
 
-std::optional<AArch64::ExtensionInfo> AArch64::parseArchExtension(StringRef ArchExt) {
-  // Resolve aliases first.
-  ArchExt = resolveExtAlias(ArchExt);
-
-  // Then find the Extension name.
+std::optional<AArch64::ExtensionInfo>
+AArch64::parseArchExtension(StringRef ArchExt) {
   for (const auto &A : Extensions) {
-    if (ArchExt == A.Name)
+    if (ArchExt == A.Name || ArchExt == A.Alias)
       return A;
   }
   return {};

llvm/utils/TableGen/ARMTargetDefEmitter.cpp

@@ -89,6 +89,10 @@ static void EmitARMTargetDef(RecordKeeper &RK, raw_ostream &OS) {
     auto AEK = Rec->getValueAsString("ArchExtKindSpelling").upper();
     OS << "  ";
     OS << "{\"" << Rec->getValueAsString("MArchName") << "\"";
+    if (auto Alias = Rec->getValueAsString("MArchAlias"); Alias.empty())
+      OS << ", {}";
+    else
+      OS << ", \"" << Alias << "\"";
     OS << ", AArch64::" << AEK;
     if (AEK == "AEK_NONE") {
       // HACK: don't emit posfeat/negfeat strings for FMVOnlyExtensions.
@@ -102,7 +106,7 @@ static void EmitARMTargetDef(RecordKeeper &RK, raw_ostream &OS) {
     OS << ", " << (uint64_t)Rec->getValueAsInt("FMVPriority");
     OS << "},\n";
   };
-  OS << "  {\"none\", AArch64::AEK_NONE, {}, {}, FEAT_INIT, \"\", "
+  OS << "  {\"none\", {}, AArch64::AEK_NONE, {}, {}, FEAT_INIT, \"\", "
         "ExtensionInfo::MaxFMVPriority},\n";
   OS << "};\n"
      << "#undef EMIT_EXTENSIONS\n"