[ARM] Tidy-up ARMAsmParser. NFC.

[javed.absar]

Summary

Move getDRegFromQReg generic function from ARMAsmParser to Utils where it belongs.

[javed.absar]

Ping!

[asb]

Why not use MCRegisterInfo::getSubReg for this purpose, thus avoiding repeating information that's already present in ARMRegisterInfo.td? MRI->getSubReg(QReg, ARM::dsub_0) should replace the functionality of getDRegFromQReg.

[javed.absar]

In D37118#852522, @asb wrote:

Why not use MCRegisterInfo::getSubReg for this purpose, thus avoiding repeating information that's already present in ARMRegisterInfo.td? MRI->getSubReg(QReg, ARM::dsub_0) should replace the functionality of getDRegFromQReg.

That's a good idea. Have done that instead. I don't see other uses of this function otherwise moving it to Utils as earlier would have been better i think.

[fhahn]

Would it be possible to just used MRI->getSubReg(QReg, ARM::dsub_0) wherever getDRegFromQReg is called? It does not seem like having a getDRegFromQReg function adds much value now.

[javed.absar]

In D37118#852732, @fhahn wrote:

Would it be possible to just used MRI->getSubReg(QReg, ARM::dsub_0) wherever getDRegFromQReg is called? It does not seem like having a getDRegFromQReg function adds much value now.

I count 8 instance of it being called, so woulld really prefer a separate function for clarity and let the compiler inline it.

[asb]

Looks good to me. I agree it seems almost unnecessary to have a helper for MRI->getSubReg(QReg, ARM::dsub_0), but as Javed points out it's called many times and getDRegFromQReg is much more readable.

[fhahn]

LGTM, using MRI->getSubReg seems much better! Thanks @asb for pointing that out, I assume there is still more potential for re-using more general functions in the ARM backend

lib/Target/ARM/AsmParser/ARMAsmParser.cpp

268

this could be a const function I think?

[javed.absar]

lib/Target/ARM/AsmParser/ARMAsmParser.cpp

268

Yes indeed. Will do so before committing

lib/Target/ARM/AsmParser/ARMAsmParser.cpp

class ARMAsmParser : public MCTargetAsmParser {
   // If we were at the first slot, this closes the IT block.
   void discardImplicitITBlock() {
     assert(inImplicitITBlock());
     assert(ITState.CurPosition == 1);
     ITState.CurPosition = ~0U;
     return;
   }
 
+  // Return the low-subreg of a given Q register.
+  unsigned getDRegFromQReg(unsigned QReg) {
+    return MRI->getSubReg(QReg, ARM::dsub_0);
+  }
+
   // Get the encoding of the IT mask, as it will appear in an IT instruction.
   unsigned getITMaskEncoding() {
     assert(inITBlock());
     unsigned Mask = ITState.Mask;
     unsigned TZ = countTrailingZeros(Mask);
     if ((ITState.Cond & 1) == 0) {
       assert(Mask && TZ <= 3 && "illegal IT mask value!");
       Mask ^= (0xE << TZ) & 0xF;
static unsigned getNextRegister(unsigned Reg) {
   case ARM::R6:  return ARM::R7;  case ARM::R7:  return ARM::R8;
   case ARM::R8:  return ARM::R9;  case ARM::R9:  return ARM::R10;
   case ARM::R10: return ARM::R11; case ARM::R11: return ARM::R12;
   case ARM::R12: return ARM::SP;  case ARM::SP:  return ARM::LR;
   case ARM::LR:  return ARM::PC;  case ARM::PC:  return ARM::R0;
   }
 }
 
-// Return the low-subreg of a given Q register.
-static unsigned getDRegFromQReg(unsigned QReg) {
-  switch (QReg) {
-  default: llvm_unreachable("expected a Q register!");
-  case ARM::Q0:  return ARM::D0;
-  case ARM::Q1:  return ARM::D2;
-  case ARM::Q2:  return ARM::D4;
-  case ARM::Q3:  return ARM::D6;
-  case ARM::Q4:  return ARM::D8;
-  case ARM::Q5:  return ARM::D10;
-  case ARM::Q6:  return ARM::D12;
-  case ARM::Q7:  return ARM::D14;
-  case ARM::Q8:  return ARM::D16;
-  case ARM::Q9:  return ARM::D18;
-  case ARM::Q10: return ARM::D20;
-  case ARM::Q11: return ARM::D22;
-  case ARM::Q12: return ARM::D24;
-  case ARM::Q13: return ARM::D26;
-  case ARM::Q14: return ARM::D28;
-  case ARM::Q15: return ARM::D30;
-  }
-}
-
 /// Parse a register list.
 bool ARMAsmParser::parseRegisterList(OperandVector &Operands) {
   MCAsmParser &Parser = getParser();
   if (Parser.getTok().isNot(AsmToken::LCurly))
     return TokError("Token is not a Left Curly Brace");
   SMLoc S = Parser.getTok().getLoc();
   Parser.Lex(); // Eat '{' token.
   SMLoc RegLoc = Parser.getTok().getLoc();