Index: llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
===================================================================
--- llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
+++ llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
@@ -3771,7 +3771,7 @@
 
   // 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."
@@ -5024,7 +5024,7 @@
     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);
Index: llvm/test/MC/AArch64/directives-case_insensitive.s
===================================================================
--- /dev/null
+++ llvm/test/MC/AArch64/directives-case_insensitive.s
@@ -0,0 +1,46 @@
+// 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