[AArch64][AsmParser] Show name of missing feature for system instructions

[olista01]

Summary

Parsing of the system instructions (IC, DC, AT and TLBI) uses this
function to show the required architecture when the operand is valid,
but the architecture is not enabled. Armv8.5A adds a few different
system instructions as part of optional features, so we need to extend
it to show individual features, not just base architectures.

This is NFC for now, but will be used by three different features added
in v8.5A, and will be tested by them.

Patch by David Spickett!

[SjoerdMeijer]

Looks okay to me.

lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp

2781

Coding style nit, should this be: Extension &e?

lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp

AArch64AsmParser::tryParseOptionalShiftExtend(OperandVector &Operands) {
   }
 
   E = SMLoc::getFromPointer(getLoc().getPointer() - 1);
   Operands.push_back(AArch64Operand::CreateShiftExtend(
       ShOp, MCE->getValue(), true, S, E, getContext()));
   return MatchOperand_Success;
 }
 
+static const struct Extension {
+  const char *Name;
+  const FeatureBitset Features;
+} ExtensionMap[] = {
+  { "crc",  {AArch64::FeatureCRC} },
+  { "sm4",  {AArch64::FeatureSM4} },
+  { "sha3", {AArch64::FeatureSHA3} },
+  { "sha2", {AArch64::FeatureSHA2} },
+  { "aes",  {AArch64::FeatureAES} },
+  { "crypto", {AArch64::FeatureCrypto} },
+  { "fp", {AArch64::FeatureFPARMv8} },
+  { "simd", {AArch64::FeatureNEON} },
+  { "ras", {AArch64::FeatureRAS} },
+  { "lse", {AArch64::FeatureLSE} },
+
+  // FIXME: Unsupported extensions
+  { "pan", {} },
+  { "lor", {} },
+  { "rdma", {} },
+  { "profile", {} },
+};
+
+
 static void setRequiredFeatureString(FeatureBitset FBS, std::string &Str) {
   if (FBS[AArch64::HasV8_1aOps])
     Str += "ARMv8.1a";
   else if (FBS[AArch64::HasV8_2aOps])
     Str += "ARMv8.2a";
   else if (FBS[AArch64::HasV8_3aOps])
     Str += "ARMv8.3a";
   else if (FBS[AArch64::HasV8_4aOps])
     Str += "ARMv8.4a";
-  else
-    Str += "(unknown)";
+  else if (FBS[AArch64::HasV8_5aOps])
+    Str += "ARMv8.5a";
+  else {
+    auto ext = std::find_if(std::begin(ExtensionMap),
+      std::end(ExtensionMap),
+      [&](const Extension& e)
+      // Use & in case multiple features are enabled
+      { return (FBS & e.Features) != FeatureBitset(); }
+    );
+
+    Str += ext != std::end(ExtensionMap) ? ext->Name : "(unknown)";
+  }
 }
 
 void AArch64AsmParser::createSysAlias(uint16_t Encoding, OperandVector &Operands,
                                       SMLoc S) {
   const uint16_t Op2 = Encoding & 7;
   const uint16_t Cm = (Encoding & 0x78) >> 3;
   const uint16_t Cn = (Encoding & 0x780) >> 7;
   const uint16_t Op1 = (Encoding & 0x3800) >> 11;
if (IDVal == MCLOHDirectiveName())
       parseDirectiveLOH(IDVal, Loc);
     else
       return true;
   } else
     return true;
   return false;
 }
 
-static const struct {
-  const char *Name;
-  const FeatureBitset Features;
-} ExtensionMap[] = {
-  { "crc",  {AArch64::FeatureCRC} },
-  { "sm4",  {AArch64::FeatureSM4} },
-  { "sha3", {AArch64::FeatureSHA3} },
-  { "sha2", {AArch64::FeatureSHA2} },
-  { "aes",  {AArch64::FeatureAES} },
-  { "crypto", {AArch64::FeatureCrypto} },
-  { "fp", {AArch64::FeatureFPARMv8} },
-  { "simd", {AArch64::FeatureNEON} },
-  { "ras", {AArch64::FeatureRAS} },
-  { "lse", {AArch64::FeatureLSE} },
-
-  // FIXME: Unsupported extensions
-  { "pan", {} },
-  { "lor", {} },
-  { "rdma", {} },
-  { "profile", {} },
-};
-
 static void ExpandCryptoAEK(AArch64::ArchKind ArchKind,
                             SmallVector<StringRef, 4> &RequestedExtensions) {
   const bool NoCrypto =
       (std::find(RequestedExtensions.begin(), RequestedExtensions.end(),
                  "nocrypto") != std::end(RequestedExtensions));
   const bool Crypto =
       (std::find(RequestedExtensions.begin(), RequestedExtensions.end(),
                  "crypto") != std::end(RequestedExtensions));