Handle ARMv7K as an alias, instead of fake architecture (NFC)

[tyomitch]

Summary

This follows D14577 to treat ARMv7K as an alias for ARMv7-A,
instead of an architecture in its own right.

[rengolin]

lib/Target/ARM/ARMSubtarget.cpp

156 ↗

(On Diff #40436)

I strongly oppose to going back to string parsing all over the place.

lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp

1053 ↗

(On Diff #40436)

Idem.

[tyomitch]

Thanks Renato, I see your point.

How about this?

[t.p.northover]

I'm not really sure about this. To the extent that the arch part of the triple means anything on MachO targets, it's a CPU choice (possibly with accompanying ABI upgrades, like x86_64h).

Defaulting watchOS to Cortex-A7 achieves the right thing on existing triples, but for what seem like dodgy reasons to me.

lib/Support/Triple.cpp

1378

tvOS probably ought to default to "cyclone" if anything.

[tyomitch]

Thanks Tim! One more attempt...

[t.p.northover]

That's probably OK for now, as far as I'm concerned. If and when we ever care about v7k outside watchOS we can decide what to do about it.

[tyomitch]

In D14757#293002, @t.p.northover wrote:

That's probably OK for now, as far as I'm concerned. If and when we ever care about v7k outside watchOS we can decide what to do about it.

Thanks Tim!
Do you have any comments on D14755 (the ARMv6J patch)? @rengolin suggested you took a look...

include/llvm/Support/ARMTargetParser.def

 ARM_CPU_NAME("cortex-a57", AK_ARMV8A, FK_CRYPTO_NEON_FP_ARMV8, false, AEK_CRC)
 ARM_CPU_NAME("cortex-a72", AK_ARMV8A, FK_CRYPTO_NEON_FP_ARMV8, false, AEK_CRC)
 ARM_CPU_NAME("cyclone", AK_ARMV8A, FK_CRYPTO_NEON_FP_ARMV8, false, AEK_CRC)
 // Non-standard Arch names.
 ARM_CPU_NAME("iwmmxt", AK_IWMMXT, FK_NONE, true, AEK_NONE)
 ARM_CPU_NAME("xscale", AK_XSCALE, FK_NONE, true, AEK_NONE)
 ARM_CPU_NAME("swift", AK_ARMV7S, FK_NEON_VFPV4, true,
              (AEK_HWDIVARM | AEK_HWDIV))
-ARM_CPU_NAME("cortex-a7", AK_ARMV7K, FK_NONE, true, AEK_HWDIVARM | AEK_HWDIV)
 // Invalid CPU
 ARM_CPU_NAME("invalid", AK_INVALID, FK_INVALID, true, AEK_INVALID)
 #undef ARM_CPU_NAME

lib/Support/Triple.cpp

StringRef Triple::getARMCPUForArch(StringRef MArch) const {
   case llvm::Triple::FreeBSD:
   case llvm::Triple::NetBSD:
     if (!MArch.empty() && MArch == "v6")
       return "arm1176jzf-s";
     break;
   case llvm::Triple::Win32:
     // FIXME: this is invalid for WindowsCE
     return "cortex-a9";
+  case llvm::Triple::MacOSX:
+  case llvm::Triple::IOS:
+  case llvm::Triple::WatchOS:
+    if (MArch == "v7k")
+      return "cortex-a7";
+    break;
   default:
     break;
   }
 
   if (MArch.empty())
     return StringRef();
 
   StringRef CPU = ARM::getDefaultCPU(MArch);