[TableGen] Add 'register alternative name matching' support

[dylanmckay]

Summary

This adds a new attribute which targets can set in TableGen which causes a function to be generated which matches register alternative names. This is very similar to ShouldEmitMatchRegisterName, except it works on alt names.

This patch is currently used by the out of tree part of the AVR backend. It reduces code duplication greatly, and has the effect that you do not need to hardcode altname to register mappings in C++.

It will not work on targets which have registers which share the same aliases.

[dylanmckay]

Once this is merged, I will be able to merge the AVR register description which will use it.

[dylanmckay]

Ping.

[dylanmckay]

Ping.

[hfinkel]

Minor formatting issues, otherwise LGTM.

utils/TableGen/AsmMatcherEmitter.cpp

2239

Insert white space after for.

2243

Insert white space after if

2790

Remove {}.

[dylanmckay]

Fix @hfinkel's code review points

include/llvm/Target/Target.td

class AsmParser {
   // function of the AsmParser class to call on every matched instruction.
   // This can be used to perform target specific instruction post-processing.
   string AsmParserInstCleanup  = "";
 
   // ShouldEmitMatchRegisterName - Set to false if the target needs a hand
   // written register name matcher
   bit ShouldEmitMatchRegisterName = 1;
 
+  // Set to true if the target needs a generated 'alternative register name'
+  // matcher.
+  //
+  // This generates a function which can be used to lookup registers from
+  // their aliases. This function will fail when called on targets where
+  // several registers share the same alias (i.e. not a 1:1 mapping).
+  bit ShouldEmitMatchRegisterAltName = 0;
+
   // HasMnemonicFirst - Set to false if target instructions don't always
   // start with a mnemonic as the first token.
   bit HasMnemonicFirst = 1;
 }
 def DefaultAsmParser : AsmParser;
 
 //===----------------------------------------------------------------------===//
 // AsmParserVariant - Subtargets can have multiple different assembly parsers

utils/TableGen/AsmMatcherEmitter.cpp

static void emitMatchRegisterName(CodeGenTarget &Target, Record *AsmParser,
   OS << "static unsigned MatchRegisterName(StringRef Name) {\n";
 
   StringMatcher("Name", Matches, OS).Emit();
 
   OS << "  return 0;\n";
   OS << "}\n\n";
 }
 
+/// Emit the function to match a string to the target
+/// specific register enum.
+static void emitMatchRegisterAltName(CodeGenTarget &Target, Record *AsmParser,
+                                     raw_ostream &OS) {
+  // Construct the match list.
+  std::vector<StringMatcher::StringPair> Matches;
+  const auto &Regs = Target.getRegBank().getRegisters();
+  for (const CodeGenRegister &Reg : Regs) {
+
+    auto AltNames = Reg.TheDef->getValueAsListOfStrings("AltNames");
+
+    for (auto AltName : AltNames) {
+      AltName = StringRef(AltName).trim();
+
+      // don't handle empty alternative names
+      if (AltName.empty())
+        continue;
+
+      Matches.emplace_back(AltName,
+                           "return " + utostr(Reg.EnumValue) + ";");
+    }
+  }
+
+  OS << "static unsigned MatchRegisterAltName(StringRef Name) {\n";
+
+  StringMatcher("Name", Matches, OS).Emit();
+
+  OS << "  return 0;\n";
+  OS << "}\n\n";
+}
+
 static const char *getMinimalTypeForRange(uint64_t Range) {
   assert(Range <= 0xFFFFFFFFFFFFFFFFULL && "Enum too large");
   if (Range > 0xFFFFFFFFULL)
     return "uint64_t";
   if (Range > 0xFFFF)
     return "uint32_t";
   if (Range > 0xFF)
     return "uint16_t";
void AsmMatcherEmitter::run(raw_ostream &OS) {
   // Emit the subtarget feature enumeration.
   emitSubtargetFeatureFlagEnumeration(Info, OS);
 
   // Emit the function to match a register name to number.
   // This should be omitted for Mips target
   if (AsmParser->getValueAsBit("ShouldEmitMatchRegisterName"))
     emitMatchRegisterName(Target, AsmParser, OS);
 
+  if (AsmParser->getValueAsBit("ShouldEmitMatchRegisterAltName"))
+    emitMatchRegisterAltName(Target, AsmParser, OS);
+
   OS << "#endif // GET_REGISTER_MATCHER\n\n";
 
   OS << "\n#ifdef GET_SUBTARGET_FEATURE_NAME\n";
   OS << "#undef GET_SUBTARGET_FEATURE_NAME\n\n";
 
   // Generate the helper function to get the names for subtarget features.
   emitGetSubtargetFeatureName(Info, OS);