[Sema][Atomics] Treat expected pointer in compare exchange atomics as _Nonnull

[arphaman]

Summary

This patch teaches clang that it has to emit a warning when NULL is passed as the 'expected' pointer parameter into an atomic compare exchange call.

[rjmccall]

LGTM.

cfe/trunk/lib/Sema/SemaChecking.cpp

if (i < NumVals[Form] + 1) {
         if (Form == Init || (Form == Arithmetic && ValType->isIntegerType()))
           Ty = ValType;
         else if (Form == Copy || Form == Xchg)
           Ty = ByValType;
         else if (Form == Arithmetic)
           Ty = Context.getPointerDiffType();
         else {
           Expr *ValArg = TheCall->getArg(i);
+          // Treat this argument as _Nonnull as we want to show a warning if
+          // NULL is passed into it.
+          CheckNonNullArgument(*this, ValArg, DRE->getLocStart());
           unsigned AS = 0;
           // Keep address space of non-atomic pointer type.
           if (const PointerType *PtrTy =
                   ValArg->getType()->getAs<PointerType>()) {
             AS = PtrTy->getPointeeType().getAddressSpace();
           }
           Ty = Context.getPointerType(
               Context.getAddrSpaceQualType(ValType.getUnqualifiedType(), AS));

cfe/trunk/test/Sema/atomic-ops.c

void f(_Atomic(int) *i, const _Atomic(int) *ci,
   __c11_atomic_fetch_and(d, 1, memory_order_seq_cst); // expected-error {{must be a pointer to atomic integer}}
 
   __atomic_fetch_and(i, 3, memory_order_seq_cst); // expected-error {{pointer to integer}}
   __atomic_fetch_or(I, 3, memory_order_seq_cst);
   __atomic_fetch_xor(P, 3, memory_order_seq_cst); // expected-error {{must be a pointer to integer}}
   __atomic_fetch_or(D, 3, memory_order_seq_cst); // expected-error {{must be a pointer to integer}}
   __atomic_fetch_and(s1, 3, memory_order_seq_cst); // expected-error {{must be a pointer to integer}}
 
-  _Bool cmpexch_1 = __c11_atomic_compare_exchange_strong(i, 0, 1, memory_order_seq_cst, memory_order_seq_cst);
-  _Bool cmpexch_2 = __c11_atomic_compare_exchange_strong(p, 0, (int*)1, memory_order_seq_cst, memory_order_seq_cst);
-  _Bool cmpexch_3 = __c11_atomic_compare_exchange_strong(d, (int*)0, 1, memory_order_seq_cst, memory_order_seq_cst); // expected-warning {{incompatible pointer types}}
+  _Bool cmpexch_1 = __c11_atomic_compare_exchange_strong(i, I, 1, memory_order_seq_cst, memory_order_seq_cst);
+  _Bool cmpexch_2 = __c11_atomic_compare_exchange_strong(p, P, (int*)1, memory_order_seq_cst, memory_order_seq_cst);
+  _Bool cmpexch_3 = __c11_atomic_compare_exchange_strong(d, I, 1, memory_order_seq_cst, memory_order_seq_cst); // expected-warning {{incompatible pointer types}}
   (void)__c11_atomic_compare_exchange_strong(i, CI, 1, memory_order_seq_cst, memory_order_seq_cst); // expected-warning {{passing 'const int *' to parameter of type 'int *' discards qualifiers}}
 
-  _Bool cmpexchw_1 = __c11_atomic_compare_exchange_weak(i, 0, 1, memory_order_seq_cst, memory_order_seq_cst);
-  _Bool cmpexchw_2 = __c11_atomic_compare_exchange_weak(p, 0, (int*)1, memory_order_seq_cst, memory_order_seq_cst);
-  _Bool cmpexchw_3 = __c11_atomic_compare_exchange_weak(d, (int*)0, 1, memory_order_seq_cst, memory_order_seq_cst); // expected-warning {{incompatible pointer types}}
+  _Bool cmpexchw_1 = __c11_atomic_compare_exchange_weak(i, I, 1, memory_order_seq_cst, memory_order_seq_cst);
+  _Bool cmpexchw_2 = __c11_atomic_compare_exchange_weak(p, P, (int*)1, memory_order_seq_cst, memory_order_seq_cst);
+  _Bool cmpexchw_3 = __c11_atomic_compare_exchange_weak(d, I, 1, memory_order_seq_cst, memory_order_seq_cst); // expected-warning {{incompatible pointer types}}
   (void)__c11_atomic_compare_exchange_weak(i, CI, 1, memory_order_seq_cst, memory_order_seq_cst); // expected-warning {{passing 'const int *' to parameter of type 'int *' discards qualifiers}}
 
   _Bool cmpexch_4 = __atomic_compare_exchange_n(I, I, 5, 1, memory_order_seq_cst, memory_order_seq_cst);
   _Bool cmpexch_5 = __atomic_compare_exchange_n(I, P, 5, 0, memory_order_seq_cst, memory_order_seq_cst); // expected-warning {{; dereference with *}}
   _Bool cmpexch_6 = __atomic_compare_exchange_n(I, I, P, 0, memory_order_seq_cst, memory_order_seq_cst); // expected-warning {{passing 'int **' to parameter of type 'int'}}
   (void)__atomic_compare_exchange_n(CI, I, 5, 1, memory_order_seq_cst, memory_order_seq_cst); // expected-error {{address argument to atomic operation must be a pointer to non-const type ('const int *' invalid)}}
   (void)__atomic_compare_exchange_n(I, CI, 5, 1, memory_order_seq_cst, memory_order_seq_cst); // expected-warning {{passing 'const int *' to parameter of type 'int *' discards qualifiers}}
 
void memory_checks(_Atomic(int) *Ap, int *p, int val) {
   (void)__atomic_compare_exchange_n(p, p, val, 0, memory_order_relaxed, memory_order_relaxed);
   (void)__atomic_compare_exchange_n(p, p, val, 0, memory_order_acquire, memory_order_relaxed);
   (void)__atomic_compare_exchange_n(p, p, val, 0, memory_order_consume, memory_order_relaxed);
   (void)__atomic_compare_exchange_n(p, p, val, 0, memory_order_release, memory_order_relaxed);
   (void)__atomic_compare_exchange_n(p, p, val, 0, memory_order_acq_rel, memory_order_relaxed);
   (void)__atomic_compare_exchange_n(p, p, val, 0, memory_order_seq_cst, memory_order_relaxed);
 }
 
-
+void nullPointerWarning(_Atomic(int) *Ap, int *p, int val) {
+  // The 'expected' pointer shouldn't be NULL.
+  (void)__c11_atomic_compare_exchange_strong(Ap, NULL, val, memory_order_relaxed, memory_order_relaxed); // expected-warning {{null passed to a callee that requires a non-null argument}}
+  (void)atomic_compare_exchange_weak(Ap, ((void*)0), val); // expected-warning {{null passed to a callee that requires a non-null argument}}
+  (void)__atomic_compare_exchange_n(p, NULL, val, 0, memory_order_relaxed, memory_order_relaxed); // expected-warning {{null passed to a callee that requires a non-null argument}}
+}