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PR23833, DR2140: an lvalue-to-rvalue conversion on a glvalue of type 

nullptr_t does not access memory.

We now reuse CK_NullToPointer to represent a conversion from a glvalue
of type nullptr_t to a prvalue of nullptr_t where necessary.

llvm-svn: 345562
This commit is contained in:
Richard Smith 2018-10-30 02:02:49 +00:00
parent 2f3e8b3d2e
commit d2e69dfddb
10 changed files with 81 additions and 20 deletions
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5
clang/lib/AST/Expr.cpp
View File

@ -1816,6 +1816,11 @@ ImplicitCastExpr *ImplicitCastExpr::Create(const ASTContext &C, QualType T,
void *Buffer =
C.Allocate(totalSizeToAlloc<CastExpr::BasePathSizeTy, CXXBaseSpecifier *>(
PathSize ? 1 : 0, PathSize));
// Per C++ [conv.lval]p3, lvalue-to-rvalue conversions on class and
// std::nullptr_t have special semantics not captured by CK_LValueToRValue.
assert((Kind != CK_LValueToRValue ||
!(T->isNullPtrType() || T->getAsCXXRecordDecl())) &&
"invalid type for lvalue-to-rvalue conversion");
ImplicitCastExpr *E =
new (Buffer) ImplicitCastExpr(T, Kind, Operand, PathSize, VK);
if (PathSize)

3
clang/lib/CodeGen/CGExprAgg.cpp
View File

@ -1300,7 +1300,8 @@ static bool isSimpleZero(const Expr *E, CodeGenFunction &CGF) {
// (int*)0 - Null pointer expressions.
if (const CastExpr *ICE = dyn_cast<CastExpr>(E))
return ICE->getCastKind() == CK_NullToPointer &&
CGF.getTypes().isPointerZeroInitializable(E->getType());
CGF.getTypes().isPointerZeroInitializable(E->getType()) &&
!E->HasSideEffects(CGF.getContext());
// '\0'
if (const CharacterLiteral *CL = dyn_cast<CharacterLiteral>(E))
return CL->getValue() == 0;

4
clang/lib/CodeGen/CGExprScalar.cpp
View File

@ -1895,14 +1895,14 @@ Value *ScalarExprEmitter::VisitCastExpr(CastExpr *CE) {
case CK_NullToPointer:
if (MustVisitNullValue(E))
(void) Visit(E);
CGF.EmitIgnoredExpr(E);
return CGF.CGM.getNullPointer(cast<llvm::PointerType>(ConvertType(DestTy)),
DestTy);
case CK_NullToMemberPointer: {
if (MustVisitNullValue(E))
(void) Visit(E);
CGF.EmitIgnoredExpr(E);
const MemberPointerType *MPT = CE->getType()->getAs<MemberPointerType>();
return CGF.CGM.getCXXABI().EmitNullMemberPointer(MPT);

7
clang/lib/Sema/SemaExpr.cpp
View File

@ -623,8 +623,11 @@ ExprResult Sema::DefaultLvalueConversion(Expr *E) {
if (E->getType().getObjCLifetime() == Qualifiers::OCL_Weak)
Cleanup.setExprNeedsCleanups(true);
ExprResult Res = ImplicitCastExpr::Create(Context, T, CK_LValueToRValue, E,
nullptr, VK_RValue);
// C++ [conv.lval]p3:
// If T is cv std::nullptr_t, the result is a null pointer constant.
CastKind CK = T->isNullPtrType() ? CK_NullToPointer : CK_LValueToRValue;
ExprResult Res =
ImplicitCastExpr::Create(Context, T, CK, E, nullptr, VK_RValue);
// C11 6.3.2.1p2:
// ... if the lvalue has atomic type, the value has the non-atomic version

10
clang/lib/Sema/SemaInit.cpp
View File

@ -7644,9 +7644,13 @@ InitializationSequence::Perform(Sema &S,
case SK_LValueToRValue: {
assert(CurInit.get()->isGLValue() && "cannot load from a prvalue");
CurInit = ImplicitCastExpr::Create(S.Context, Step->Type,
CK_LValueToRValue, CurInit.get(),
/*BasePath=*/nullptr, VK_RValue);
// C++ [conv.lval]p3:
// If T is cv std::nullptr_t, the result is a null pointer constant.
CastKind CK =
Step->Type->isNullPtrType() ? CK_NullToPointer : CK_LValueToRValue;
CurInit =
ImplicitCastExpr::Create(S.Context, Step->Type, CK, CurInit.get(),
/*BasePath=*/nullptr, VK_RValue);
break;
}

7
clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp
View File

@ -379,7 +379,6 @@ void ExprEngine::VisitCast(const CastExpr *CastE, const Expr *Ex,
case CK_BitCast:
case CK_AddressSpaceConversion:
case CK_BooleanToSignedIntegral:
case CK_NullToPointer:
case CK_IntegralToPointer:
case CK_PointerToIntegral: {
SVal V = state->getSVal(Ex, LCtx);
@ -502,6 +501,12 @@ void ExprEngine::VisitCast(const CastExpr *CastE, const Expr *Ex,
Bldr.generateNode(CastE, Pred, state);
continue;
}
case CK_NullToPointer: {
SVal V = svalBuilder.makeNull();
state = state->BindExpr(CastE, LCtx, V);
Bldr.generateNode(CastE, Pred, state);
continue;
}
case CK_NullToMemberPointer: {
SVal V = svalBuilder.getMemberPointer(nullptr);
state = state->BindExpr(CastE, LCtx, V);

12
clang/test/Analysis/nullptr.cpp
View File

@ -126,20 +126,12 @@ struct Type {
void shouldNotCrash() {
decltype(nullptr) p; // expected-note{{'p' declared without an initial value}}
if (getSymbol()) // expected-note {{Assuming the condition is false}}
// expected-note@-1{{Taking false branch}}
// expected-note@-2{{Assuming the condition is false}}
// expected-note@-3{{Taking false branch}}
// expected-note@-4{{Assuming the condition is true}}
// expected-note@-5{{Taking true branch}}
invokeF(p); // expected-warning{{1st function call argument is an uninitialized value}}
// expected-note@-1{{1st function call argument is an uninitialized value}}
if (getSymbol()) // expected-note {{Assuming the condition is false}}
// expected-note@-1{{Taking false branch}}
// expected-note@-2{{Assuming the condition is true}}
// expected-note@-3{{Taking true branch}}
invokeF(nullptr); // expected-note {{Calling 'invokeF'}}
// expected-note@-1{{Passing null pointer value via 1st parameter 'x'}}
invokeF(p); // expected-note {{Calling 'invokeF'}}
// expected-note@-1{{Passing null pointer value via 1st parameter 'x'}}
if (getSymbol()) { // expected-note {{Assuming the condition is true}}
// expected-note@-1{{Taking true branch}}
X *xx = Type().x; // expected-note {{Null pointer value stored to field 'x'}}

10
clang/test/CXX/drs/dr21xx.cpp
View File

@ -19,6 +19,16 @@ namespace dr2120 { // dr2120: 7
static_assert(!__is_standard_layout(E), "");
}
namespace dr2140 { // dr2140: 8
#if __cplusplus >= 201103L
union U { int a; decltype(nullptr) b; };
constexpr int *test(U u) {
return u.b;
}
static_assert(!test({123}), "u.b should be valid even when b is inactive");
#endif
}
namespace dr2180 { // dr2180: yes
class A {
A &operator=(const A &); // expected-note 0-2{{here}}

41
clang/test/CodeGenCXX/nullptr.cpp
View File

@ -22,3 +22,44 @@ void g() {
const std::type_info& f2() {
return typeid(nullptr_t);
}
union U {
int n;
nullptr_t b;
};
// CHECK-LABEL: define {{.*}}pr23833_a
// CHECK: store
// CHECK: load
// CHECK-NOT: load
// CHECK: ret i1 false
bool pr23833_a(U &u) { return u.b; }
// CHECK-LABEL: define {{.*}}pr23833_b
// CHECK: store
// CHECK: load
// CHECK-NOT: load
// CHECK: ret i8* null
nullptr_t pr23833_b(nullptr_t &n) { return n; }
struct X1 { operator int*(); };
struct X2 { operator const nullptr_t&(); };
// CHECK-LABEL: define {{.*}}pr23833_c
// CHECK: call {{.*}}X1
// CHECK: call {{.*}}X2
// CHECK-NOT: load
// CHECK: ret i32
int pr23833_c() {
return X1() != X2();
}
// CHECK-LABEL: define {{.*}}pr23833_d
// CHECK: call {{.*}}X2
// CHECK-NOT: load
// CHECK: store
// CHECK: load
// CHECK: ret i32*
int *pr23833_d() {
int *p = X2();
return p;
}

2
clang/www/cxx_dr_status.html
View File

@ -12655,7 +12655,7 @@ and <I>POD class</I></td>
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#2140">2140</a></td>
<td>CD4</td>
<td>Lvalue-to-rvalue conversion of <TT>std::nullptr_t</TT></td>
<td class="none" align="center">Unknown</td>
<td class="svn" align="center">SVN</td>
</tr>
<tr id="2141">
<td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#2141">2141</a></td>