diff --git a/clang/lib/Driver/ToolChains/Arch/AArch64.cpp b/clang/lib/Driver/ToolChains/Arch/AArch64.cpp
--- a/clang/lib/Driver/ToolChains/Arch/AArch64.cpp
+++ b/clang/lib/Driver/ToolChains/Arch/AArch64.cpp
@@ -106,6 +106,31 @@
    return true;
 }
 
+// Add the default target features implied by the architecture
+// version. We should agree with GCC on these. A summary of the
+// features can be found at
+// https://gcc.gnu.org/onlinedocs/gcc/AArch64-Options.html#AArch64-Options,
+// under the description of the option `-march=name`.
+static void AddAArch64DefaultFeatures(std::vector<StringRef> &Features,
+                                      llvm::AArch64::ArchKind ArchKind) {
+  switch (ArchKind) {
+  case llvm::AArch64::ArchKind::ARMV8_6A:
+    Features.push_back("+i8mm");
+    Features.push_back("+bf16");
+    LLVM_FALLTHROUGH;
+  case llvm::AArch64::ArchKind::ARMV8_5A:
+    Features.push_back("+sb");
+    Features.push_back("+ssbs");
+    Features.push_back("+predres");
+    LLVM_FALLTHROUGH;
+  // TODO: sort out the remaining cases from 8.4a to 8a. Update test
+  // cases in clang/test/Driver/aarch64-march-default-features.c
+  // accordingly.
+  default:
+    break;
+  }
+}
+
 static bool
 getAArch64ArchFeaturesFromMarch(const Driver &D, StringRef March,
                                 const ArgList &Args,
@@ -114,10 +139,15 @@
   std::pair<StringRef, StringRef> Split = StringRef(MarchLowerCase).split("+");
 
   llvm::AArch64::ArchKind ArchKind = llvm::AArch64::parseArch(Split.first);
-  if (ArchKind == llvm::AArch64::ArchKind::INVALID ||
-      !llvm::AArch64::getArchFeatures(ArchKind, Features) ||
-      (Split.second.size() &&
-       !DecodeAArch64Features(D, Split.second, Features, ArchKind)))
+
+  if (!llvm::AArch64::getArchFeatures(ArchKind, Features))
+    return false;
+
+  assert(ArchKind != llvm::AArch64::ArchKind::INVALID &&
+         "Invalid architecture.");
+  AddAArch64DefaultFeatures(Features, ArchKind);
+
+  if (!DecodeAArch64Features(D, Split.second, Features, ArchKind))
     return false;
 
   return true;
diff --git a/clang/test/Driver/aarch64-cpus.c b/clang/test/Driver/aarch64-cpus.c
--- a/clang/test/Driver/aarch64-cpus.c
+++ b/clang/test/Driver/aarch64-cpus.c
@@ -643,7 +643,7 @@
 // GENERICV85A-BE: "-cc1"{{.*}} "-triple" "aarch64_be{{.*}}" "-target-cpu" "generic" "-target-feature" "+neon" "-target-feature" "+v8.5a"
 
 // RUN: %clang -target aarch64 -march=armv8.5-a+fp16 -### -c %s 2>&1 | FileCheck -check-prefix=GENERICV85A-FP16 %s
-// GENERICV85A-FP16: "-cc1"{{.*}} "-triple" "aarch64{{.*}}" "-target-cpu" "generic" "-target-feature" "+neon" "-target-feature" "+v8.5a" "-target-feature" "+fullfp16"
+// GENERICV85A-FP16: "-cc1"{{.*}} "-triple" "aarch64{{.*}}" "-target-cpu" "generic" "-target-feature" "+neon" "-target-feature" "+v8.5a" "-target-feature" "+sb" "-target-feature" "+ssbs" "-target-feature" "+predres" "-target-feature" "+fullfp16"
 
 // RUN: %clang -target aarch64 -march=armv8.6a -### -c %s 2>&1 | FileCheck -check-prefix=GENERICV86A %s
 // RUN: %clang -target aarch64 -march=armv8.6-a -### -c %s 2>&1 | FileCheck -check-prefix=GENERICV86A %s
diff --git a/clang/test/Driver/aarch64-march-default-features.c b/clang/test/Driver/aarch64-march-default-features.c
new file mode 100644
--- /dev/null
+++ b/clang/test/Driver/aarch64-march-default-features.c
@@ -0,0 +1,27 @@
+// RUN: %clang -target aarch64-linux-gnu -march=armv8.6a        -### -c %s 2>&1 | FileCheck %s --check-prefixes=CHECK-8_6,CHECK-8_5
+// RUN: %clang -target aarch64-linux-gnu -march=armv8.6a+nobf16 -### -c %s 2>&1 | FileCheck %s --check-prefix=CHECK-8_6-NOBF16
+// RUN: %clang -target aarch64-linux-gnu -march=armv8.6a+noi8mm -### -c %s 2>&1 | FileCheck %s --check-prefix=CHECK-8_6-NOI8MM
+
+// CHECK-8_6:             "-target-feature" "+i8mm" "-target-feature" "+bf16"
+// CHECK-8_6-NOBF16-NOT:                            "-target-feature" "+bf16"
+// CHECK-8_6-NOBF16:      "-target-feature" "+i8mm"
+// CHECK-8_6-NOBF16-SAME:                           "-target-feature" "-bf16"
+// CHECK-8_6-NOI8MM-NOT:  "-target-feature" "+i8mm"
+// CHECK-8_6-NOI8MM:                                "-target-feature" "+bf16"
+// CHECK-8_6-NOI8MM-SAME: "-target-feature" "-i8mm"
+
+// RUN: %clang -target aarch64-linux-gnu -march=armv8.5a           -### -c %s 2>&1 | FileCheck %s --check-prefixes=CHECK-8_5
+// RUN: %clang -target aarch64-linux-gnu -march=armv8.5a+nosb      -### -c %s 2>&1 | FileCheck %s --check-prefix=CHECK-8_5-NOSB
+// RUN: %clang -target aarch64-linux-gnu -march=armv8.5a+nossbs    -### -c %s 2>&1 | FileCheck %s --check-prefix=CHECK-8_5-NOSSBS
+// RUN: %clang -target aarch64-linux-gnu -march=armv8.5a+nopredres -### -c %s 2>&1 | FileCheck %s --check-prefix=CHECK-8_5-NOPREDRES
+
+// CHECK-8_5:                "-target-feature" "+sb" "-target-feature" "+ssbs" "-target-feature" "+predres"
+// CHECK-8_5-NOSB-NOT:       "-target-feature" "+sb"
+// CHECK-8_5-NOSB:                                   "-target-feature" "+ssbs" "-target-feature" "+predres"
+// CHECK-8_5-NOSB-SAME:      "-target-feature" "-sb"
+// CHECK-8_5-NOSSBS-NOT:                             "-target-feature" "+ssbs"
+// CHECK-8_5-NOSSBS:         "-target-feature" "+sb"                           "-target-feature" "+predres"
+// CHECK-8_5-NOSSBS-SAME:                            "-target-feature" "-ssbs"
+// CHECK-8_5-NOPREDRES-NOT:                                                    "-target-feature" "+predres"
+// CHECK-8_5-NOPREDRES:      "-target-feature" "+sb" "-target-feature" "+ssbs"
+// CHECK-8_5-NOPREDRES-SAME:                                                   "-target-feature" "-predres"