[AARCH64] Fix a comment to match the code. NFC.

[mstorsjo]

Summary

For the ELF case, the default/preferred form is the generic one, not the short one as used for Apple - fix the comment to say so. Currently it is a copy-paste typo.

Make the comments on the darwin default a bit more verbose.

Use enum names instead of literal 0/1 to further increase readability and reduce fragility.

[kristof.beyls]

LGTM, even if you don't implement the nitpicky suggestions I made.

lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.cpp

35

you could add " when targeting Darwin" to the comment.

71

You could add " when targeting ELF" to the comment.

lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.cpp

 
 static cl::opt<AsmWriterVariantTy> AsmWriterVariant(
     "aarch64-neon-syntax", cl::init(Default),
     cl::desc("Choose style of NEON code to emit from AArch64 backend:"),
     cl::values(clEnumValN(Generic, "generic", "Emit generic NEON assembly"),
                clEnumValN(Apple, "apple", "Emit Apple-style NEON assembly")));
 
 AArch64MCAsmInfoDarwin::AArch64MCAsmInfoDarwin() {
-  // We prefer NEON instructions to be printed in the short form.
-  AssemblerDialect = AsmWriterVariant == Default ? 1 : AsmWriterVariant;
+  // We prefer NEON instructions to be printed in the short, apple-specific form.
+  AssemblerDialect = AsmWriterVariant == Default ? Apple : AsmWriterVariant;
 
   PrivateGlobalPrefix = "L";
   PrivateLabelPrefix = "L";
   SeparatorString = "%%";
   CommentString = ";";
   CodePointerSize = CalleeSaveStackSlotSize = 8;
 
   AlignmentIsInBytes = false;
const MCExpr *AArch64MCAsmInfoDarwin::getExprForPersonalitySymbol(
   const MCExpr *PC = MCSymbolRefExpr::create(PCSym, Context);
   return MCBinaryExpr::createSub(Res, PC, Context);
 }
 
 AArch64MCAsmInfoELF::AArch64MCAsmInfoELF(const Triple &T) {
   if (T.getArch() == Triple::aarch64_be)
     IsLittleEndian = false;
 
-  // We prefer NEON instructions to be printed in the short form.
-  AssemblerDialect = AsmWriterVariant == Default ? 0 : AsmWriterVariant;
+  // We prefer NEON instructions to be printed in the generic form.
+  AssemblerDialect = AsmWriterVariant == Default ? Generic : AsmWriterVariant;
 
   CodePointerSize = 8;
 
   // ".comm align is in bytes but .align is pow-2."
   AlignmentIsInBytes = false;
 
   CommentString = "//";
   PrivateGlobalPrefix = ".L";