[AArch64] Make AArch64 specific assembly directives case insensitive

[ostannard]

LGTM

llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp

Name = StringSwitch<StringRef>(Name.lower())
              .Case("bgt", "b.gt")
              .Case("ble", "b.le")
              .Case("bal", "b.al")
              .Case("bnv", "b.nv")
              .Default(Name);
 
   // First check for the AArch64-specific .req directive.
   if (Parser.getTok().is(AsmToken::Identifier) &&
-      Parser.getTok().getIdentifier() == ".req") {
+      Parser.getTok().getIdentifier().lower() == ".req") {
     parseDirectiveReq(Name, NameLoc);
     // We always return 'error' for this, as we're done with this
     // statement and don't need to match the 'instruction."
     return true;
   }
 
   // Create the leading tokens for the mnemonic, split by '.' characters.
   size_t Start = 0, Next = Name.find('.');

 }
 
 /// ParseDirective parses the arm specific directives
 bool AArch64AsmParser::ParseDirective(AsmToken DirectiveID) {
   const MCObjectFileInfo::Environment Format =
     getContext().getObjectFileInfo()->getObjectFileType();
   bool IsMachO = Format == MCObjectFileInfo::IsMachO;
 
-  StringRef IDVal = DirectiveID.getIdentifier();
+  auto IDVal = DirectiveID.getIdentifier().lower();
   SMLoc Loc = DirectiveID.getLoc();
   if (IDVal == ".arch")
     parseDirectiveArch(Loc);
   else if (IDVal == ".cpu")
     parseDirectiveCPU(Loc);
   else if (IDVal == ".tlsdesccall")
     parseDirectiveTLSDescCall(Loc);
   else if (IDVal == ".ltorg" || IDVal == ".pool")

llvm/test/MC/AArch64/directives-case_insensitive.s

+// RUN: llvm-mc -triple aarch64-none-linux-gnu -filetype asm -o - %s 2>&1 | FileCheck %s
+
+.CPU generic+lse
+casa  w5, w7, [x20]
+// CHECK: casa  w5, w7, [x20]
+
+.ARCH_EXTENSION crc
+crc32cx w0, w1, x3
+// CHECK: crc32cx w0, w1, x3
+
+.ARCH armv8.4-a
+tlbi vmalle1os
+// CHECK: tlbi  vmalle1os
+
+.INST 0x5e104020
+// CHECK: .inst 0x5e104020
+
+.RELOC 0, R_AARCH64_NONE, 8
+// CHECK: .reloc 0, R_AARCH64_NONE, 8
+
+.HWORD 0x1234
+// CHECK: .hword  4660
+.WORD  0x12345678
+// CHECK: .word 305419896
+.DWORD 0x1234567812345678
+// CHECK: .xword  1311768465173141112
+.XWORD 0x1234567812345678
+// CHECK: .xword  1311768465173141112
+
+fred .REQ x5
+.UNREQ fred
+
+.CFI_STARTPROC
+.CFI_NEGATE_RA_STATE
+.CFI_B_KEY_FRAME
+.CFI_ENDPROC
+// CHECK: .cfi_startproc
+// CHECK: .cfi_negate_ra_state
+// CHECK: .cfi_b_key_frame
+// CHECK: .cfi_endproc
+
+.TLSDESCCALL var
+// CHECK: .tlsdesccall var
+
+.LTORG
+.POOL