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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.

This reinstates r345562, reverted in r346065, now that CodeGen's
handling of non-odr-used variables has been fixed.

llvm-svn: 363337
This commit is contained in:
Richard Smith 2019-06-13 23:31:04 +00:00
parent b1027a480a
commit 0476d069e3
10 changed files with 86 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
clang/lib/AST/Expr.cpp
View File

@ -1885,6 +1885,11 @@ ImplicitCastExpr *ImplicitCastExpr::Create(const ASTContext &C, QualType T,
ExprValueKind VK) {
unsigned PathSize = (BasePath ? BasePath->size() : 0);
void *Buffer = C.Allocate(totalSizeToAlloc<CXXBaseSpecifier *>(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

@ -1352,7 +1352,8 @@ 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

@ -2148,14 +2148,14 @@ 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);

6
clang/lib/Sema/SemaExpr.cpp
View File

@ -635,8 +635,10 @@ ExprResult Sema::DefaultLvalueConversion(Expr *E) {
if (E->getType().getObjCLifetime() == Qualifiers::OCL_Weak)
Cleanup.setExprNeedsCleanups(true);
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;
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

8
clang/lib/Sema/SemaInit.cpp
View File

@ -7779,8 +7779,12 @@ ExprResult 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(),
// 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

@ -378,7 +378,6 @@ 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);
@ -503,6 +502,12 @@ 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);

10
clang/test/Analysis/nullptr.cpp
View File

@ -126,19 +126,11 @@ 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'}}
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}}

10
clang/test/CXX/drs/dr21xx.cpp
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@ -32,6 +32,16 @@ namespace dr2120 { // dr2120: 7
static_assert(!__is_standard_layout(E), "");
}
namespace dr2140 { // dr2140: 9
#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 dr2170 { // dr2170: 9
#if __cplusplus >= 201103L
void f() {

47
clang/test/CodeGenCXX/nullptr.cpp
View File

@ -22,3 +22,50 @@ 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;
}
namespace PR39528 {
constexpr nullptr_t null = nullptr;
void f(nullptr_t);
void g() { f(null); }
}

2
clang/www/cxx_dr_status.html
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@ -12655,7 +12655,7 @@ and <I>POD class</I></td>
<td><a href="http://wg21.link/cwg2140">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://wg21.link/cwg2141">2141</a></td>