text: // RUN: %clang_cc1 %s -emit-llvm -o - -triple=armv5-unknown-freebsd -std=c11 | FileCheck %s
  
  // Test that we are generating atomicrmw instructions, rather than
  // compare-exchange loops for common atomic ops.  This makes a big difference
  // on RISC platforms, where the compare-exchange loop becomes a ll/sc pair for
  // the load and then another ll/sc in the loop, expanding to about 30
  // instructions when it should be only 4.  It has a smaller, but still
  // noticeable, impact on platforms like x86 and RISC-V, where there are atomic
  // RMW instructions.
  //
  // We currently emit cmpxchg loops for most operations on _Bools, because
  // they're sufficiently rare that it's not worth making sure that the semantics
  // are correct.
  
  struct elem;
  
  struct ptr {
      struct elem *ptr;
  };
  // CHECK-DAG: %struct.ptr = type { %struct.elem* }
  
  struct elem {
      _Atomic(struct ptr) link;
  };
  // CHECK-DAG: %struct.elem = type { %struct.ptr }
  
  struct ptr object;
  // CHECK-DAG: @object = common global %struct.ptr zeroinitializer
  
  // CHECK-DAG: @testStructGlobal = global {{.*}} { i16 1, i16 2, i16 3, i16 4 }
  // CHECK-DAG: @testPromotedStructGlobal = global {{.*}} { %{{.*}} { i16 1, i16 2, i16 3 }, [2 x i8] zeroinitializer }
  
  
  typedef int __attribute__((vector_size(16))) vector;
  
  _Atomic(_Bool) b;
  _Atomic(int) i;
  _Atomic(long long) l;
  _Atomic(short) s;
  _Atomic(char*) p;
  _Atomic(float) f;
  _Atomic(vector) v;
  
  // CHECK: testinc
  void testinc(void)
  {
    // Special case for suffix bool++, sets to true and returns the old value.
    // CHECK: atomicrmw xchg i8* @b, i8 1 seq_cst
    b++;
    // CHECK: atomicrmw add i32* @i, i32 1 seq_cst
    i++;
    // CHECK: atomicrmw add i64* @l, i64 1 seq_cst
    l++;
    // CHECK: atomicrmw add i16* @s, i16 1 seq_cst
    s++;
    // Prefix increment
    // Special case for bool: set to true and return true
    // CHECK: store atomic i8 1, i8* @b seq_cst, align 1
    ++b;
    // Currently, we have no variant of atomicrmw that returns the new value, so
    // we have to generate an atomic add, which returns the old value, and then a
    // non-atomic add.
    // CHECK: atomicrmw add i32* @i, i32 1 seq_cst
    // CHECK: add i32 
    ++i;
    // CHECK: atomicrmw add i64* @l, i64 1 seq_cst
    // CHECK: add i64
    ++l;
    // CHECK: atomicrmw add i16* @s, i16 1 seq_cst
    // CHECK: add i16
    ++s;
  }
  // CHECK: testdec
  void testdec(void)
  {
    // CHECK: call arm_aapcscc zeroext i1 @__atomic_compare_exchange(i32 1, i8* @b
    b--;
    // CHECK: atomicrmw sub i32* @i, i32 1 seq_cst
    i--;
    // CHECK: atomicrmw sub i64* @l, i64 1 seq_cst
    l--;
    // CHECK: atomicrmw sub i16* @s, i16 1 seq_cst
    s--;
    // CHECK: call arm_aapcscc zeroext i1 @__atomic_compare_exchange(i32 1, i8* @b
    --b;
    // CHECK: atomicrmw sub i32* @i, i32 1 seq_cst
    // CHECK: sub i32
    --i;
    // CHECK: atomicrmw sub i64* @l, i64 1 seq_cst
    // CHECK: sub i64
    --l;
    // CHECK: atomicrmw sub i16* @s, i16 1 seq_cst
    // CHECK: sub i16
    --s;
  }
  // CHECK: testaddeq
  void testaddeq(void)
  {
    // CHECK: call arm_aapcscc zeroext i1 @__atomic_compare_exchange(i32 1, i8* @b
    // CHECK: atomicrmw add i32* @i, i32 42 seq_cst
    // CHECK: atomicrmw add i64* @l, i64 42 seq_cst
    // CHECK: atomicrmw add i16* @s, i16 42 seq_cst
    b += 42;
    i += 42;
    l += 42;
    s += 42;
  }
  // CHECK: testsubeq
  void testsubeq(void)
  {
    // CHECK: call arm_aapcscc zeroext i1 @__atomic_compare_exchange(i32 1, i8* @b
    // CHECK: atomicrmw sub i32* @i, i32 42 seq_cst
    // CHECK: atomicrmw sub i64* @l, i64 42 seq_cst
    // CHECK: atomicrmw sub i16* @s, i16 42 seq_cst
    b -= 42;
    i -= 42;
    l -= 42;
    s -= 42;
  }
  // CHECK: testxoreq
  void testxoreq(void)
  {
    // CHECK: call arm_aapcscc zeroext i1 @__atomic_compare_exchange(i32 1, i8* @b
    // CHECK: atomicrmw xor i32* @i, i32 42 seq_cst
    // CHECK: atomicrmw xor i64* @l, i64 42 seq_cst
    // CHECK: atomicrmw xor i16* @s, i16 42 seq_cst
    b ^= 42;
    i ^= 42;
    l ^= 42;
    s ^= 42;
  }
  // CHECK: testoreq
  void testoreq(void)
  {
    // CHECK: call arm_aapcscc zeroext i1 @__atomic_compare_exchange(i32 1, i8* @b
    // CHECK: atomicrmw or i32* @i, i32 42 seq_cst
    // CHECK: atomicrmw or i64* @l, i64 42 seq_cst
    // CHECK: atomicrmw or i16* @s, i16 42 seq_cst
    b |= 42;
    i |= 42;
    l |= 42;
    s |= 42;
  }
  // CHECK: testandeq
  void testandeq(void)
  {
    // CHECK: call arm_aapcscc zeroext i1 @__atomic_compare_exchange(i32 1, i8* @b
    // CHECK: atomicrmw and i32* @i, i32 42 seq_cst
    // CHECK: atomicrmw and i64* @l, i64 42 seq_cst
    // CHECK: atomicrmw and i16* @s, i16 42 seq_cst
    b &= 42;
    i &= 42;
    l &= 42;
    s &= 42;
  }
  
  // CHECK-LABEL: define arm_aapcscc void @testFloat(float*
  void testFloat(_Atomic(float) *fp) {
  // CHECK:      [[FP:%.*]] = alloca float*
  // CHECK-NEXT: [[X:%.*]] = alloca float
  // CHECK-NEXT: [[F:%.*]] = alloca float
  // CHECK-NEXT: [[TMP0:%.*]] = alloca float
  // CHECK-NEXT: [[TMP1:%.*]] = alloca float
  // CHECK-NEXT: store float* {{%.*}}, float** [[FP]]
  
  // CHECK-NEXT: [[T0:%.*]] = load float*, float** [[FP]]
  // CHECK-NEXT: store float 1.000000e+00, float* [[T0]], align 4
    __c11_atomic_init(fp, 1.0f);
  
  // CHECK-NEXT: store float 2.000000e+00, float* [[X]], align 4
    _Atomic(float) x = 2.0f;
  
  // CHECK-NEXT: [[T0:%.*]] = load float*, float** [[FP]]
  // CHECK-NEXT: [[T1:%.*]] = bitcast float* [[T0]] to i8*
  // CHECK-NEXT: [[T2:%.*]] = bitcast float* [[TMP0]] to i8*
  // CHECK-NEXT: call arm_aapcscc void @__atomic_load(i32 4, i8* [[T1]], i8* [[T2]], i32 5)
  // CHECK-NEXT: [[T3:%.*]] = load float, float* [[TMP0]], align 4
  // CHECK-NEXT: store float [[T3]], float* [[F]]
    float f = *fp;
  
  // CHECK-NEXT: [[T0:%.*]] = load float, float* [[F]], align 4
  // CHECK-NEXT: [[T1:%.*]] = load float*, float** [[FP]], align 4
  // CHECK-NEXT: store float [[T0]], float* [[TMP1]], align 4
  // CHECK-NEXT: [[T2:%.*]] = bitcast float* [[T1]] to i8*
  // CHECK-NEXT: [[T3:%.*]] = bitcast float* [[TMP1]] to i8*
  // CHECK-NEXT: call arm_aapcscc void @__atomic_store(i32 4, i8* [[T2]], i8* [[T3]], i32 5)
    *fp = f;
  
  // CHECK-NEXT: ret void
  }
  
  // CHECK: define arm_aapcscc void @testComplexFloat([[CF:{ float, float }]]*
  void testComplexFloat(_Atomic(_Complex float) *fp) {
  // CHECK:      [[FP:%.*]] = alloca [[CF]]*, align 4
  // CHECK-NEXT: [[X:%.*]] = alloca [[CF]], align 8
  // CHECK-NEXT: [[F:%.*]] = alloca [[CF]], align 4
  // CHECK-NEXT: [[TMP0:%.*]] = alloca [[CF]], align 8
  // CHECK-NEXT: [[TMP1:%.*]] = alloca [[CF]], align 8
  // CHECK-NEXT: store [[CF]]*
  
  // CHECK-NEXT: [[P:%.*]] = load [[CF]]*, [[CF]]** [[FP]]
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[CF]], [[CF]]* [[P]], i32 0, i32 0
  // CHECK-NEXT: [[T1:%.*]] = getelementptr inbounds [[CF]], [[CF]]* [[P]], i32 0, i32 1
  // CHECK-NEXT: store float 1.000000e+00, float* [[T0]]
  // CHECK-NEXT: store float 0.000000e+00, float* [[T1]]
    __c11_atomic_init(fp, 1.0f);
  
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[CF]], [[CF]]* [[X]], i32 0, i32 0
  // CHECK-NEXT: [[T1:%.*]] = getelementptr inbounds [[CF]], [[CF]]* [[X]], i32 0, i32 1
  // CHECK-NEXT: store float 2.000000e+00, float* [[T0]]
  // CHECK-NEXT: store float 0.000000e+00, float* [[T1]]
    _Atomic(_Complex float) x = 2.0f;
  
  // CHECK-NEXT: [[T0:%.*]] = load [[CF]]*, [[CF]]** [[FP]]
  // CHECK-NEXT: [[T1:%.*]] = bitcast [[CF]]* [[T0]] to i8*
  // CHECK-NEXT: [[T2:%.*]] = bitcast [[CF]]* [[TMP0]] to i8*
  // CHECK-NEXT: call arm_aapcscc void @__atomic_load(i32 8, i8* [[T1]], i8* [[T2]], i32 5)
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[CF]], [[CF]]* [[TMP0]], i32 0, i32 0
  // CHECK-NEXT: [[R:%.*]] = load float, float* [[T0]]
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[CF]], [[CF]]* [[TMP0]], i32 0, i32 1
  // CHECK-NEXT: [[I:%.*]] = load float, float* [[T0]]
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[CF]], [[CF]]* [[F]], i32 0, i32 0
  // CHECK-NEXT: [[T1:%.*]] = getelementptr inbounds [[CF]], [[CF]]* [[F]], i32 0, i32 1
  // CHECK-NEXT: store float [[R]], float* [[T0]]
  // CHECK-NEXT: store float [[I]], float* [[T1]]
    _Complex float f = *fp;
  
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[CF]], [[CF]]* [[F]], i32 0, i32 0
  // CHECK-NEXT: [[R:%.*]] = load float, float* [[T0]]
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[CF]], [[CF]]* [[F]], i32 0, i32 1
  // CHECK-NEXT: [[I:%.*]] = load float, float* [[T0]]
  // CHECK-NEXT: [[DEST:%.*]] = load [[CF]]*, [[CF]]** [[FP]], align 4
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[CF]], [[CF]]* [[TMP1]], i32 0, i32 0
  // CHECK-NEXT: [[T1:%.*]] = getelementptr inbounds [[CF]], [[CF]]* [[TMP1]], i32 0, i32 1
  // CHECK-NEXT: store float [[R]], float* [[T0]]
  // CHECK-NEXT: store float [[I]], float* [[T1]]
  // CHECK-NEXT: [[T0:%.*]] = bitcast [[CF]]* [[DEST]] to i8*
  // CHECK-NEXT: [[T1:%.*]] = bitcast [[CF]]* [[TMP1]] to i8*
  // CHECK-NEXT: call arm_aapcscc void @__atomic_store(i32 8, i8* [[T0]], i8* [[T1]], i32 5)
    *fp = f;
  
  // CHECK-NEXT: ret void
  }
  
  typedef struct { short x, y, z, w; } S;
  _Atomic S testStructGlobal = (S){1, 2, 3, 4};
  // CHECK: define arm_aapcscc void @testStruct([[S:.*]]*
  void testStruct(_Atomic(S) *fp) {
  // CHECK:      [[FP:%.*]] = alloca [[S]]*, align 4
  // CHECK-NEXT: [[X:%.*]] = alloca [[S]], align 8
  // CHECK-NEXT: [[F:%.*]] = alloca [[S:%.*]], align 2
  // CHECK-NEXT: [[TMP0:%.*]] = alloca [[S]], align 8
  // CHECK-NEXT: store [[S]]*
  
  // CHECK-NEXT: [[P:%.*]] = load [[S]]*, [[S]]** [[FP]]
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[S]], [[S]]* [[P]], i32 0, i32 0
  // CHECK-NEXT: store i16 1, i16* [[T0]], align 2
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[S]], [[S]]* [[P]], i32 0, i32 1
  // CHECK-NEXT: store i16 2, i16* [[T0]], align 2
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[S]], [[S]]* [[P]], i32 0, i32 2
  // CHECK-NEXT: store i16 3, i16* [[T0]], align 2
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[S]], [[S]]* [[P]], i32 0, i32 3
  // CHECK-NEXT: store i16 4, i16* [[T0]], align 2
    __c11_atomic_init(fp, (S){1,2,3,4});
  
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[S]], [[S]]* [[X]], i32 0, i32 0
  // CHECK-NEXT: store i16 1, i16* [[T0]], align 2
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[S]], [[S]]* [[X]], i32 0, i32 1
  // CHECK-NEXT: store i16 2, i16* [[T0]], align 2
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[S]], [[S]]* [[X]], i32 0, i32 2
  // CHECK-NEXT: store i16 3, i16* [[T0]], align 2
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[S]], [[S]]* [[X]], i32 0, i32 3
  // CHECK-NEXT: store i16 4, i16* [[T0]], align 2
    _Atomic(S) x = (S){1,2,3,4};
  
  // CHECK-NEXT: [[T0:%.*]] = load [[S]]*, [[S]]** [[FP]]
  // CHECK-NEXT: [[T1:%.*]] = bitcast [[S]]* [[T0]] to i8*
  // CHECK-NEXT: [[T2:%.*]] = bitcast [[S]]* [[F]] to i8*
  // CHECK-NEXT: call arm_aapcscc void @__atomic_load(i32 8, i8* [[T1]], i8* [[T2]], i32 5)
    S f = *fp;
  
  // CHECK-NEXT: [[T0:%.*]] = load [[S]]*, [[S]]** [[FP]]
  // CHECK-NEXT: [[T1:%.*]] = bitcast [[S]]* [[TMP0]] to i8*
  // CHECK-NEXT: [[T2:%.*]] = bitcast [[S]]* [[F]] to i8*
  // CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i32(i8* [[T1]], i8* [[T2]], i32 8, i32 2, i1 false)
  // CHECK-NEXT: [[T3:%.*]] = bitcast [[S]]* [[T0]] to i8*
  // CHECK-NEXT: [[T4:%.*]] = bitcast [[S]]* [[TMP0]] to i8*
  // CHECK-NEXT: call arm_aapcscc void @__atomic_store(i32 8, i8* [[T3]], i8* [[T4]], i32 5)
    *fp = f;
  
  // CHECK-NEXT: ret void
  }
  
  typedef struct { short x, y, z; } PS;
  _Atomic PS testPromotedStructGlobal = (PS){1, 2, 3};
  // CHECK: define arm_aapcscc void @testPromotedStruct([[APS:.*]]*
  void testPromotedStruct(_Atomic(PS) *fp) {
  // CHECK:      [[FP:%.*]] = alloca [[APS]]*, align 4
  // CHECK-NEXT: [[X:%.*]] = alloca [[APS]], align 8
  // CHECK-NEXT: [[F:%.*]] = alloca [[PS:%.*]], align 2
  // CHECK-NEXT: [[TMP0:%.*]] = alloca [[APS]], align 8
  // CHECK-NEXT: [[TMP1:%.*]] = alloca [[APS]], align 8
  // CHECK-NEXT: [[A:%.*]] = alloca i32, align 4
  // CHECK-NEXT: [[TMP2:%.*]] = alloca %struct.PS, align 2
  // CHECK-NEXT: [[TMP3:%.*]] = alloca [[APS]], align 8
  // CHECK-NEXT: store [[APS]]*
  
  // CHECK-NEXT: [[P:%.*]] = load [[APS]]*, [[APS]]** [[FP]]
  // CHECK-NEXT: [[T0:%.*]] = bitcast [[APS]]* [[P]] to i8*
  // CHECK-NEXT: call void @llvm.memset.p0i8.i64(i8* [[T0]], i8 0, i64 8, i32 8, i1 false)
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[APS]], [[APS]]* [[P]], i32 0, i32 0
  // CHECK-NEXT: [[T1:%.*]] = getelementptr inbounds [[PS]], [[PS]]* [[T0]], i32 0, i32 0
  // CHECK-NEXT: store i16 1, i16* [[T1]], align 2
  // CHECK-NEXT: [[T1:%.*]] = getelementptr inbounds [[PS]], [[PS]]* [[T0]], i32 0, i32 1
  // CHECK-NEXT: store i16 2, i16* [[T1]], align 2
  // CHECK-NEXT: [[T1:%.*]] = getelementptr inbounds [[PS]], [[PS]]* [[T0]], i32 0, i32 2
  // CHECK-NEXT: store i16 3, i16* [[T1]], align 2
    __c11_atomic_init(fp, (PS){1,2,3});
  
  // CHECK-NEXT: [[T0:%.*]] = bitcast [[APS]]* [[X]] to i8*
  // CHECK-NEXT: call void @llvm.memset.p0i8.i32(i8* [[T0]], i8 0, i32 8, i32 8, i1 false)
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[APS]], [[APS]]* [[X]], i32 0, i32 0
  // CHECK-NEXT: [[T1:%.*]] = getelementptr inbounds [[PS]], [[PS]]* [[T0]], i32 0, i32 0
  // CHECK-NEXT: store i16 1, i16* [[T1]], align 2
  // CHECK-NEXT: [[T1:%.*]] = getelementptr inbounds [[PS]], [[PS]]* [[T0]], i32 0, i32 1
  // CHECK-NEXT: store i16 2, i16* [[T1]], align 2
  // CHECK-NEXT: [[T1:%.*]] = getelementptr inbounds [[PS]], [[PS]]* [[T0]], i32 0, i32 2
  // CHECK-NEXT: store i16 3, i16* [[T1]], align 2
    _Atomic(PS) x = (PS){1,2,3};
  
  // CHECK-NEXT: [[T0:%.*]] = load [[APS]]*, [[APS]]** [[FP]]
  // CHECK-NEXT: [[T1:%.*]] = bitcast [[APS]]* [[T0]] to i8*
  // CHECK-NEXT: [[T2:%.*]] = bitcast [[APS]]* [[TMP0]] to i8*
  // CHECK-NEXT: call arm_aapcscc void @__atomic_load(i32 8, i8* [[T1]], i8* [[T2]], i32 5)
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[APS]], [[APS]]* [[TMP0]], i32 0, i32 0
  // CHECK-NEXT: [[T1:%.*]] = bitcast [[PS]]* [[F]] to i8*
  // CHECK-NEXT: [[T2:%.*]] = bitcast [[PS]]* [[T0]] to i8*
  // CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i32(i8* [[T1]], i8* [[T2]], i32 6, i32 2, i1 false)
    PS f = *fp;
  
  // CHECK-NEXT: [[T0:%.*]] = load [[APS]]*, [[APS]]** [[FP]]
  // CHECK-NEXT: [[T1:%.*]] = bitcast { %struct.PS, [2 x i8] }* [[TMP1]] to i8*
  // CHECK-NEXT: call void @llvm.memset.p0i8.i32(i8* [[T1]], i8 0, i32 8, i32 8, i1 false)
  // CHECK-NEXT: [[T1:%.*]] = getelementptr inbounds [[APS]], [[APS]]* [[TMP1]], i32 0, i32 0
  // CHECK-NEXT: [[T2:%.*]] = bitcast [[PS]]* [[T1]] to i8*
  // CHECK-NEXT: [[T3:%.*]] = bitcast [[PS]]* [[F]] to i8*
  // CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i32(i8* [[T2]], i8* [[T3]], i32 6, i32 2, i1 false)
  // CHECK-NEXT: [[T4:%.*]] = bitcast [[APS]]* [[T0]] to i8*
  // CHECK-NEXT: [[T5:%.*]] = bitcast [[APS]]* [[TMP1]] to i8*
  // CHECK-NEXT: call arm_aapcscc void @__atomic_store(i32 8, i8* [[T4]], i8* [[T5]], i32 5)
    *fp = f;
  
  // CHECK-NEXT: [[T0:%.*]] = load [[APS]]*, [[APS]]** [[FP]], align 4
  // CHECK-NEXT: [[T1:%.*]] = bitcast [[APS]]* [[T0]] to i8*
  // CHECK-NEXT: [[T2:%.*]] = bitcast [[APS]]* [[TMP3]] to i8*
  // CHECK-NEXT: call arm_aapcscc void @__atomic_load(i32 8, i8* [[T1]], i8* [[T2]], i32 5)
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[APS]], [[APS]]* [[TMP3]], i32 0, i32 0
  // CHECK-NEXT: [[T1:%.*]] = bitcast %struct.PS* [[TMP2]] to i8*
  // CHECK-NEXT: [[T2:%.*]] = bitcast %struct.PS* [[T0]] to i8*
  // CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i32(i8* [[T1]], i8* [[T2]], i32 6, i32 2, i1 false)
  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds %struct.PS, %struct.PS* [[TMP2]], i32 0, i32 0
  // CHECK-NEXT: [[T1:%.*]] = load i16, i16* [[T0]], align 2
  // CHECK-NEXT: [[T2:%.*]] = sext i16 [[T1]] to i32
  // CHECK-NEXT: store i32 [[T2]], i32* [[A]], align 4
    int a = ((PS)*fp).x;
  
  // CHECK-NEXT: ret void
  }
  
  // CHECK: define arm_aapcscc void @testPromotedStructOps([[APS:.*]]*
  
  // FIXME: none of these look right, but we can leave the "test" here
  // to make sure they at least don't crash.
  void testPromotedStructOps(_Atomic(PS) *p) {
    PS a = __c11_atomic_load(p, 5);
    __c11_atomic_store(p, a, 5);
    PS b = __c11_atomic_exchange(p, a, 5);
    _Bool v = __c11_atomic_compare_exchange_strong(p, &b, a, 5, 5);
    v = __c11_atomic_compare_exchange_weak(p, &b, a, 5, 5);
  }
  