Index: clang/lib/Basic/Targets/PPC.h
===================================================================
--- clang/lib/Basic/Targets/PPC.h
+++ clang/lib/Basic/Targets/PPC.h
@@ -78,6 +78,7 @@
   bool IsISA2_07 = false;
   bool IsISA3_0 = false;
   bool IsISA3_1 = false;
+  bool HasQuadwordAtomics = false;
 
 protected:
   std::string ABI;
@@ -443,6 +444,14 @@
     MaxAtomicPromoteWidth = MaxAtomicInlineWidth = 64;
   }
 
+  void setMaxAtomicWidth() override {
+    // For layout on Linux, we support up to 16 bytes.
+    if (getTriple().isOSLinux() && hasFeature("quadword-atomics")) {
+      MaxAtomicPromoteWidth = 128;
+      MaxAtomicInlineWidth = 128;
+    }
+  }
+
   BuiltinVaListKind getBuiltinVaListKind() const override {
     return TargetInfo::CharPtrBuiltinVaList;
   }
Index: clang/lib/Basic/Targets/PPC.cpp
===================================================================
--- clang/lib/Basic/Targets/PPC.cpp
+++ clang/lib/Basic/Targets/PPC.cpp
@@ -81,6 +81,8 @@
       IsISA3_0 = true;
     } else if (Feature == "+isa-v31-instructions") {
       IsISA3_1 = true;
+    } else if (Feature == "+quadword-atomics") {
+      HasQuadwordAtomics = true;
     }
     // TODO: Finish this list and add an assert that we've handled them
     // all.
@@ -544,6 +546,12 @@
   Features["isa-v30-instructions"] =
       llvm::StringSwitch<bool>(CPU).Case("pwr9", true).Default(false);
 
+  Features["quadword-atomics"] =
+      getTriple().isArch64Bit() && llvm::StringSwitch<bool>(CPU)
+                                       .Case("pwr9", true)
+                                       .Case("pwr8", true)
+                                       .Default(false);
+
   // Power10 includes all the same features as Power9 plus any features specific
   // to the Power10 core.
   if (CPU == "pwr10" || CPU == "power10") {
@@ -654,6 +662,7 @@
       .Case("isa-v207-instructions", IsISA2_07)
       .Case("isa-v30-instructions", IsISA3_0)
       .Case("isa-v31-instructions", IsISA3_1)
+      .Case("quadword-atomics", HasQuadwordAtomics)
       .Default(false);
 }
 
Index: clang/test/CodeGen/PowerPC/atomic-alignment.c
===================================================================
--- clang/test/CodeGen/PowerPC/atomic-alignment.c
+++ clang/test/CodeGen/PowerPC/atomic-alignment.c
@@ -2,6 +2,8 @@
 // RUN:   FileCheck %s --check-prefixes=PPC,PPC32
 // RUN: %clang_cc1 -verify -triple powerpc64le-unknown-linux -emit-llvm -o - %s | \
 // RUN:   FileCheck %s --check-prefixes=PPC,PPC64
+// RUN: %clang_cc1 -verify -triple powerpc64le-unknown-linux -target-cpu pwr8 \
+// RUN:   -emit-llvm -o - %s | FileCheck %s --check-prefixes=PPC,PPC64-PWR8
 // RUN: %clang_cc1 -verify -triple powerpc64-unknown-aix -emit-llvm -o - %s | \
 // RUN:   FileCheck %s --check-prefixes=PPC,PPC64
 
@@ -16,6 +18,7 @@
 
 // PPC32: @l = global i32 0, align 4{{$}}
 // PPC64: @l = global i64 0, align 8{{$}}
+// PPC64-PWR8: @l = global i64 0, align 8{{$}}
 _Atomic(long) l; // expected-no-diagnostics
 
 // PPC: @ll = global i64 0, align 8{{$}}
@@ -27,11 +30,14 @@
 
 // PPC32: @o = global %struct.O zeroinitializer, align 1{{$}}
 // PPC64: @o = global %struct.O zeroinitializer, align 8{{$}}
+// PPC64-PWR8: @o = global %struct.O zeroinitializer, align 8{{$}}
 _Atomic(O) o; // expected-no-diagnostics
 
 typedef struct {
   char x[16];
 } Q;
 
-// PPC: @q = global %struct.Q zeroinitializer, align 1{{$}}
+// PPC32: @q = global %struct.Q zeroinitializer, align 1{{$}}
+// PPC64: @q = global %struct.Q zeroinitializer, align 1{{$}}
+// PPC64-PWR8: @q = global %struct.Q zeroinitializer, align 16{{$}}
 _Atomic(Q) q; // expected-no-diagnostics
Index: clang/test/CodeGen/PowerPC/quadword-atomics.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/PowerPC/quadword-atomics.c
@@ -0,0 +1,90 @@
+// RUN: %clang_cc1 -verify -Wno-atomic-alignment -triple powerpc64le-linux-gnu \
+// RUN:   -target-cpu pwr8 -emit-llvm -o - %s | FileCheck %s --check-prefix=PPC64-PWR8
+// RUN: %clang_cc1 -verify -Wno-atomic-alignment -triple powerpc64le-linux-gnu \
+// RUN:   -emit-llvm -o - %s | FileCheck %s --check-prefix=PPC64
+
+typedef struct {
+  char x[16];
+} Q;
+
+typedef _Atomic(Q) AtomicQ;
+
+typedef __int128_t int128_t;
+
+// PPC64-PWR8-LABEL: @test_load(
+// PPC64-PWR8:    [[TMP3:%.*]] = load atomic i128, i128* [[TMP1:%.*]] acquire, align 16
+//
+// PPC64-LABEL: @test_load(
+// PPC64:    call void @__atomic_load(i64 noundef 16, i8* noundef [[TMP3:%.*]], i8* noundef [[TMP4:%.*]], i32 noundef signext 2)
+//
+Q test_load(AtomicQ *ptr) {
+  // expected-no-diagnostics
+  return __c11_atomic_load(ptr, __ATOMIC_ACQUIRE);
+}
+
+// PPC64-PWR8-LABEL: @test_store(
+// PPC64-PWR8:    store atomic i128 [[TMP6:%.*]], i128* [[TMP4:%.*]] release, align 16
+//
+// PPC64-LABEL: @test_store(
+// PPC64:    call void @__atomic_store(i64 noundef 16, i8* noundef [[TMP6:%.*]], i8* noundef [[TMP7:%.*]], i32 noundef signext 3)
+//
+void test_store(Q val, AtomicQ *ptr) {
+  // expected-no-diagnostics
+  __c11_atomic_store(ptr, val, __ATOMIC_RELEASE);
+}
+
+// PPC64-PWR8-LABEL: @test_add(
+// PPC64-PWR8:    [[TMP3:%.*]] = atomicrmw add i128* [[TMP0:%.*]], i128 [[TMP2:%.*]] monotonic, align 16
+//
+// PPC64-LABEL: @test_add(
+// PPC64:    [[CALL:%.*]] = call i128 @__atomic_fetch_add_16(i8* noundef [[TMP2:%.*]], i128 noundef [[TMP3:%.*]], i32 noundef signext 0)
+//
+void test_add(int128_t *ptr, int128_t x) {
+  // expected-no-diagnostics
+  __c11_atomic_fetch_add((_Atomic(int128_t) *)ptr, x, __ATOMIC_RELAXED);
+}
+
+// PPC64-PWR8-LABEL: @test_xchg(
+// PPC64-PWR8:    [[TMP8:%.*]] = atomicrmw xchg i128* [[TMP4:%.*]], i128 [[TMP7:%.*]] seq_cst, align 16
+//
+// PPC64-LABEL: @test_xchg(
+// PPC64:    call void @__atomic_exchange(i64 noundef 16, i8* noundef [[TMP7:%.*]], i8* noundef [[TMP8:%.*]], i8* noundef [[TMP9:%.*]], i32 noundef signext 5)
+//
+Q test_xchg(AtomicQ *ptr, Q new) {
+  // expected-no-diagnostics
+  return __c11_atomic_exchange(ptr, new, __ATOMIC_SEQ_CST);
+}
+
+// PPC64-PWR8-LABEL: @test_cmpxchg(
+// PPC64-PWR8:    [[TMP10:%.*]] = cmpxchg i128* [[TMP5:%.*]], i128 [[TMP8:%.*]], i128 [[TMP9:%.*]] seq_cst monotonic, align 16
+//
+// PPC64-LABEL: @test_cmpxchg(
+// PPC64:    [[CALL:%.*]] = call zeroext i1 @__atomic_compare_exchange(i64 noundef 16, i8* noundef [[TMP8:%.*]], i8* noundef [[TMP9:%.*]], i8* noundef [[TMP10:%.*]], i32 noundef signext 5, i32 noundef signext 0)
+//
+int test_cmpxchg(AtomicQ *ptr, Q *cmp, Q new) {
+  // expected-no-diagnostics
+  return __c11_atomic_compare_exchange_strong(ptr, cmp, new, __ATOMIC_SEQ_CST, __ATOMIC_RELAXED);
+}
+
+// PPC64-PWR8-LABEL: @test_cmpxchg_weak(
+// PPC64-PWR8:    [[TMP10:%.*]] = cmpxchg weak i128* [[TMP5:%.*]], i128 [[TMP8:%.*]], i128 [[TMP9:%.*]] seq_cst monotonic, align 16
+//
+// PPC64-LABEL: @test_cmpxchg_weak(
+// PPC64:    [[CALL:%.*]] = call zeroext i1 @__atomic_compare_exchange(i64 noundef 16, i8* noundef [[TMP8:%.*]], i8* noundef [[TMP9:%.*]], i8* noundef [[TMP10:%.*]], i32 noundef signext 5, i32 noundef signext 0)
+//
+int test_cmpxchg_weak(AtomicQ *ptr, Q *cmp, Q new) {
+  // expected-no-diagnostics
+  return __c11_atomic_compare_exchange_weak(ptr, cmp, new, __ATOMIC_SEQ_CST, __ATOMIC_RELAXED);
+}
+
+// PPC64-PWR8-LABEL: @is_lock_free(
+// PPC64-PWR8:    ret i32 1
+//
+// PPC64-LABEL: @is_lock_free(
+// PPC64:    [[CALL:%.*]] = call zeroext i1 @__atomic_is_lock_free(i64 noundef 16, i8* noundef null)
+//
+int is_lock_free() {
+  AtomicQ q;
+ // expected-no-diagnostics
+  return __c11_atomic_is_lock_free(sizeof(q));
+}
Index: clang/test/Sema/atomic-ops.c
===================================================================
--- clang/test/Sema/atomic-ops.c
+++ clang/test/Sema/atomic-ops.c
@@ -9,7 +9,7 @@
 // RUN:   -target-cpu pwr7
 // RUN: %clang_cc1 %s -verify -fgnuc-version=4.2.1 -ffreestanding \
 // RUN:   -fsyntax-only -triple=powerpc64le-linux-gnu -std=c11 \
-// RUN:   -target-cpu pwr8
+// RUN:   -target-cpu pwr8 -DPPC64_PWR8
 
 // Basic parsing/Sema tests for __c11_atomic_*
 
@@ -47,7 +47,11 @@
 _Static_assert(__c11_atomic_is_lock_free(3), ""); // expected-error {{not an integral constant expression}}
 _Static_assert(__c11_atomic_is_lock_free(4), "");
 _Static_assert(__c11_atomic_is_lock_free(8), "");
+#ifndef PPC64_PWR8
 _Static_assert(__c11_atomic_is_lock_free(16), ""); // expected-error {{not an integral constant expression}}
+#else
+_Static_assert(__c11_atomic_is_lock_free(16), ""); // expected-no-error
+#endif
 _Static_assert(__c11_atomic_is_lock_free(17), ""); // expected-error {{not an integral constant expression}}
 
 _Static_assert(__atomic_is_lock_free(1, 0), "");
@@ -55,15 +59,23 @@
 _Static_assert(__atomic_is_lock_free(3, 0), ""); // expected-error {{not an integral constant expression}}
 _Static_assert(__atomic_is_lock_free(4, 0), "");
 _Static_assert(__atomic_is_lock_free(8, 0), "");
+#ifndef PPC64_PWR8
 _Static_assert(__atomic_is_lock_free(16, 0), ""); // expected-error {{not an integral constant expression}}
+#else
+_Static_assert(__atomic_is_lock_free(16, 0), ""); // expected-no-error
+#endif
 _Static_assert(__atomic_is_lock_free(17, 0), ""); // expected-error {{not an integral constant expression}}
 
 _Static_assert(atomic_is_lock_free((atomic_char*)0), "");
 _Static_assert(atomic_is_lock_free((atomic_short*)0), "");
 _Static_assert(atomic_is_lock_free((atomic_int*)0), "");
 _Static_assert(atomic_is_lock_free((atomic_long*)0), "");
+#ifndef PPC64_PWR8
 // noi128-error@+1 {{__int128 is not supported on this target}}
 _Static_assert(atomic_is_lock_free((_Atomic(__int128)*)0), ""); // expected-error {{not an integral constant expression}}
+#else
+_Static_assert(atomic_is_lock_free((_Atomic(__int128)*)0), ""); // expected-no-error
+#endif
 _Static_assert(atomic_is_lock_free(0 + (atomic_char*)0), "");
 
 char i8;
@@ -88,7 +100,11 @@
 _Static_assert(!__atomic_always_lock_free(3, 0), "");
 _Static_assert(__atomic_always_lock_free(4, 0), "");
 _Static_assert(__atomic_always_lock_free(8, 0), "");
+#ifndef PPC64_PWR8
 _Static_assert(!__atomic_always_lock_free(16, 0), "");
+#else
+_Static_assert(__atomic_always_lock_free(16, 0), "");
+#endif
 _Static_assert(!__atomic_always_lock_free(17, 0), "");
 
 _Static_assert(__atomic_always_lock_free(1, incomplete), "");
Index: llvm/lib/Target/PowerPC/PPCISelLowering.cpp
===================================================================
--- llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -123,7 +123,7 @@
 
 static cl::opt<bool> EnableQuadwordAtomics(
     "ppc-quadword-atomics",
-    cl::desc("enable quadword lock-free atomic operations"), cl::init(false),
+    cl::desc("enable quadword lock-free atomic operations"), cl::init(true),
     cl::Hidden);
 
 static cl::opt<bool>