Index: clang/lib/Basic/Targets/AArch64.h
===================================================================
--- clang/lib/Basic/Targets/AArch64.h
+++ clang/lib/Basic/Targets/AArch64.h
@@ -44,6 +44,7 @@
   bool HasSVE2BitPerm;
   bool HasMatmulFP64;
   bool HasMatmulFP32;
+  bool HasLSE;
 
   llvm::AArch64::ArchKind ArchKind;
 
Index: clang/lib/Basic/Targets/AArch64.cpp
===================================================================
--- clang/lib/Basic/Targets/AArch64.cpp
+++ clang/lib/Basic/Targets/AArch64.cpp
@@ -155,8 +155,9 @@
 
 void AArch64TargetInfo::getTargetDefinesARMV81A(const LangOptions &Opts,
                                                 MacroBuilder &Builder) const {
-  // FIXME: Armv8.1 makes __ARM_FEATURE_CRC32 mandatory. Handle it here.
   Builder.defineMacro("__ARM_FEATURE_QRDMX", "1");
+  Builder.defineMacro("__ARM_FEATURE_ATOMICS", "1");
+  Builder.defineMacro("__ARM_FEATURE_CRC32", "1");
 }
 
 void AArch64TargetInfo::getTargetDefinesARMV82A(const LangOptions &Opts,
@@ -176,8 +177,6 @@
 void AArch64TargetInfo::getTargetDefinesARMV84A(const LangOptions &Opts,
                                                 MacroBuilder &Builder) const {
   // Also include the Armv8.3 defines
-  // FIXME: Armv8.4 makes __ARM_FEATURE_ATOMICS, defined in GCC, mandatory.
-  // Add and handle it here.
   getTargetDefinesARMV83A(Opts, Builder);
 }
 
@@ -304,6 +303,9 @@
   if (HasMatMul)
     Builder.defineMacro("__ARM_FEATURE_MATMUL_INT8", "1");
 
+  if (HasLSE)
+    Builder.defineMacro("__ARM_FEATURE_ATOMICS", "1");
+
   if (HasBFloat16) {
     Builder.defineMacro("__ARM_FEATURE_BF16", "1");
     Builder.defineMacro("__ARM_FEATURE_BF16_VECTOR_ARITHMETIC", "1");
@@ -416,6 +418,7 @@
   HasSVE2BitPerm = false;
   HasMatmulFP64 = false;
   HasMatmulFP32 = false;
+  HasLSE = false;
 
   ArchKind = llvm::AArch64::ArchKind::ARMV8A;
 
@@ -497,6 +500,8 @@
       HasMatMul = true;
     if (Feature == "+bf16")
       HasBFloat16 = true;
+    if (Feature == "+lse")
+      HasLSE = true;
   }
 
   setDataLayout();
Index: clang/test/Preprocessor/aarch64-target-features.c
===================================================================
--- clang/test/Preprocessor/aarch64-target-features.c
+++ clang/test/Preprocessor/aarch64-target-features.c
@@ -62,6 +62,8 @@
 // RUN: %clang -target arm64-none-linux-gnu -mcrc -x c -E -dM %s -o - | FileCheck --check-prefix=CHECK-CRC32 %s
 // RUN: %clang -target aarch64-none-linux-gnu -march=armv8-a+crc -x c -E -dM %s -o - | FileCheck --check-prefix=CHECK-CRC32 %s
 // RUN: %clang -target arm64-none-linux-gnu -march=armv8-a+crc -x c -E -dM %s -o - | FileCheck --check-prefix=CHECK-CRC32 %s
+// RUN: %clang -target aarch64-none-linux-gnu -march=armv8.1-a -x c -E -dM %s -o - | FileCheck --check-prefix=CHECK-CRC32 %s
+// RUN: %clang -target arm64-none-linux-gnu -march=armv8.1-a -x c -E -dM %s -o - | FileCheck --check-prefix=CHECK-CRC32 %s
 // CHECK-CRC32: __ARM_FEATURE_CRC32 1
 
 // RUN: %clang -target aarch64-none-linux-gnu -fno-math-errno -fno-signed-zeros\
@@ -451,3 +453,10 @@
 // CHECK-SVE-VECTOR-BITS-512: __ARM_FEATURE_SVE_BITS 512
 // CHECK-SVE-VECTOR-BITS-1024: __ARM_FEATURE_SVE_BITS 1024
 // CHECK-SVE-VECTOR-BITS-2048: __ARM_FEATURE_SVE_BITS 2048
+
+// ================== Check Largse System Extensions (LSE)
+// RUN: %clang -target aarch64-none-linux-gnu -march=armv8-a+lse -x c -E -dM %s -o - | FileCheck --check-prefix=CHECK-LSE %s
+// RUN: %clang -target arm64-none-linux-gnu -march=armv8-a+lse -x c -E -dM %s -o - | FileCheck --check-prefix=CHECK-LSE %s
+// RUN: %clang -target aarch64-none-linux-gnu -march=armv8.1-a -x c -E -dM %s -o - | FileCheck --check-prefix=CHECK-LSE %s
+// RUN: %clang -target arm64-none-linux-gnu -march=armv8.1-a -x c -E -dM %s -o - | FileCheck --check-prefix=CHECK-LSE %s
+// CHECK-LSE: __ARM_FEATURE_ATOMICS 1