ahatanak created this revision.
ahatanak added a subscriber: cfe-commits.
clang currently errors out when a lambda expression is used to compute the size
of an array even though clang supports variable-length arrays as a C99
extension. For example,
$ cat vla1.cpp
```
int foo3();
struct S1 {
virtual ~S1();
};
struct S2 : S1 {
};
void foo(S1 *s1) {
unsigned char a1[([](int a) {return a; })(1)];
unsigned char a2[foo3()]; // This is OK.
unsigned char a3[!dynamic_cast<S2 *>(s1) + 1]; // This is OK.
}
```
$ clang++ vla1.cpp -c -std=c++11
vla1.cpp:11:21: error: a lambda expression may not appear inside of a constant
expression
unsigned char a1[([](int a) {return a; })(1)];
^
1 error generated.
To handle VLAs in a more consistent way, this patch makes changes to allow
lambda expressions to be used for array bounds if it is in a BlockContext.
http://reviews.llvm.org/D21187
Files:
include/clang/Parse/Parser.h
include/clang/Sema/Sema.h
lib/Parse/ParseDecl.cpp
lib/Parse/ParseExpr.cpp
lib/Sema/Sema.cpp
lib/Sema/SemaExpr.cpp
test/SemaCXX/lambda-expressions.cpp
Index: test/SemaCXX/lambda-expressions.cpp
===================================================================
--- test/SemaCXX/lambda-expressions.cpp
+++ test/SemaCXX/lambda-expressions.cpp
@@ -499,3 +499,12 @@
};
}
}
+
+namespace array_bound {
+void foo() {
+ int a0[([](){ return 4; })()];
+ int a2[([](int n){ return n; })(4)];
+}
+
+int a2[([](){ return 4; })()]; // expected-error {{a lambda expression may not appear inside of a constant expression}} expected-error {{variable length array declaration not allowed at file scope}}
+}
Index: lib/Sema/SemaExpr.cpp
===================================================================
--- lib/Sema/SemaExpr.cpp
+++ lib/Sema/SemaExpr.cpp
@@ -12791,10 +12791,10 @@
void
Sema::PushExpressionEvaluationContext(ExpressionEvaluationContext NewContext,
Decl *LambdaContextDecl,
- bool IsDecltype) {
+ bool IsDecltype, bool IsArrayBound) {
ExprEvalContexts.emplace_back(NewContext, ExprCleanupObjects.size(),
ExprNeedsCleanups, LambdaContextDecl,
- IsDecltype);
+ IsDecltype, IsArrayBound);
ExprNeedsCleanups = false;
if (!MaybeODRUseExprs.empty())
std::swap(MaybeODRUseExprs, ExprEvalContexts.back().SavedMaybeODRUseExprs);
@@ -12814,21 +12814,22 @@
if (!Rec.Lambdas.empty()) {
if (Rec.isUnevaluated() || Rec.Context == ConstantEvaluated) {
- unsigned D;
if (Rec.isUnevaluated()) {
// C++11 [expr.prim.lambda]p2:
// A lambda-expression shall not appear in an unevaluated operand
// (Clause 5).
- D = diag::err_lambda_unevaluated_operand;
- } else {
+ for (const auto *L : Rec.Lambdas)
+ Diag(L->getLocStart(), diag::err_lambda_unevaluated_operand);
+ // Don't error out on lambdas used to compute array size in a
+ // BlockContext.
+ } else if (!Rec.IsArrayBound) {
// C++1y [expr.const]p2:
// A conditional-expression e is a core constant expression unless the
// evaluation of e, following the rules of the abstract machine, would
// evaluate [...] a lambda-expression.
- D = diag::err_lambda_in_constant_expression;
+ for (const auto *L : Rec.Lambdas)
+ Diag(L->getLocStart(), diag::err_lambda_in_constant_expression);
}
- for (const auto *L : Rec.Lambdas)
- Diag(L->getLocStart(), D);
} else {
// Mark the capture expressions odr-used. This was deferred
// during lambda expression creation.
Index: lib/Sema/Sema.cpp
===================================================================
--- lib/Sema/Sema.cpp
+++ lib/Sema/Sema.cpp
@@ -124,7 +124,8 @@
// Tell diagnostics how to render things from the AST library.
Diags.SetArgToStringFn(&FormatASTNodeDiagnosticArgument, &Context);
- ExprEvalContexts.emplace_back(PotentiallyEvaluated, 0, false, nullptr, false);
+ ExprEvalContexts.emplace_back(PotentiallyEvaluated, 0, false, nullptr, false,
+ false);
FunctionScopes.push_back(new FunctionScopeInfo(Diags));
Index: lib/Parse/ParseExpr.cpp
===================================================================
--- lib/Parse/ParseExpr.cpp
+++ lib/Parse/ParseExpr.cpp
@@ -194,13 +194,14 @@
}
-ExprResult Parser::ParseConstantExpression(TypeCastState isTypeCast) {
+ExprResult Parser::ParseConstantExpression(TypeCastState isTypeCast,
+ bool IsArrayBound) {
// C++03 [basic.def.odr]p2:
// An expression is potentially evaluated unless it appears where an
// integral constant expression is required (see 5.19) [...].
// C++98 and C++11 have no such rule, but this is only a defect in C++98.
- EnterExpressionEvaluationContext Unevaluated(Actions,
- Sema::ConstantEvaluated);
+ EnterExpressionEvaluationContext Unevaluated(Actions, Sema::ConstantEvaluated,
+ nullptr, false, IsArrayBound);
ExprResult LHS(ParseCastExpression(false, false, isTypeCast));
ExprResult Res(ParseRHSOfBinaryExpression(LHS, prec::Conditional));
Index: lib/Parse/ParseDecl.cpp
===================================================================
--- lib/Parse/ParseDecl.cpp
+++ lib/Parse/ParseDecl.cpp
@@ -6103,7 +6103,8 @@
// Parse the constant-expression or assignment-expression now (depending
// on dialect).
if (getLangOpts().CPlusPlus) {
- NumElements = ParseConstantExpression();
+ NumElements = ParseConstantExpression(
+ Parser::NotTypeCast, D.getContext() == Declarator::BlockContext);
} else {
EnterExpressionEvaluationContext Unevaluated(Actions,
Sema::ConstantEvaluated);
Index: include/clang/Sema/Sema.h
===================================================================
--- include/clang/Sema/Sema.h
+++ include/clang/Sema/Sema.h
@@ -854,6 +854,9 @@
/// suffice, e.g., in a default function argument.
Decl *ManglingContextDecl;
+ /// \brief Whether an array bound in a BlockContext is being parsed.
+ bool IsArrayBound;
+
/// \brief The context information used to mangle lambda expressions
/// and block literals within this context.
///
@@ -873,11 +876,12 @@
unsigned NumCleanupObjects,
bool ParentNeedsCleanups,
Decl *ManglingContextDecl,
- bool IsDecltype)
+ bool IsDecltype, bool IsArrayBound)
: Context(Context), ParentNeedsCleanups(ParentNeedsCleanups),
IsDecltype(IsDecltype), NumCleanupObjects(NumCleanupObjects),
NumTypos(0),
- ManglingContextDecl(ManglingContextDecl), MangleNumbering() { }
+ ManglingContextDecl(ManglingContextDecl),
+ IsArrayBound(IsArrayBound), MangleNumbering() {}
/// \brief Retrieve the mangling numbering context, used to consistently
/// number constructs like lambdas for mangling.
@@ -3639,7 +3643,8 @@
void PushExpressionEvaluationContext(ExpressionEvaluationContext NewContext,
Decl *LambdaContextDecl = nullptr,
- bool IsDecltype = false);
+ bool IsDecltype = false,
+ bool IsArrayBound = false);
enum ReuseLambdaContextDecl_t { ReuseLambdaContextDecl };
void PushExpressionEvaluationContext(ExpressionEvaluationContext NewContext,
ReuseLambdaContextDecl_t,
@@ -9494,10 +9499,11 @@
EnterExpressionEvaluationContext(Sema &Actions,
Sema::ExpressionEvaluationContext NewContext,
Decl *LambdaContextDecl = nullptr,
- bool IsDecltype = false)
+ bool IsDecltype = false,
+ bool IsArrayBound = false)
: Actions(Actions) {
Actions.PushExpressionEvaluationContext(NewContext, LambdaContextDecl,
- IsDecltype);
+ IsDecltype, IsArrayBound);
}
EnterExpressionEvaluationContext(Sema &Actions,
Sema::ExpressionEvaluationContext NewContext,
Index: include/clang/Parse/Parser.h
===================================================================
--- include/clang/Parse/Parser.h
+++ include/clang/Parse/Parser.h
@@ -1396,7 +1396,8 @@
};
ExprResult ParseExpression(TypeCastState isTypeCast = NotTypeCast);
- ExprResult ParseConstantExpression(TypeCastState isTypeCast = NotTypeCast);
+ ExprResult ParseConstantExpression(TypeCastState isTypeCast = NotTypeCast,
+ bool IsArrayBound = false);
ExprResult ParseConstraintExpression();
// Expr that doesn't include commas.
ExprResult ParseAssignmentExpression(TypeCastState isTypeCast = NotTypeCast);
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