Arcoth created this revision.
Arrays of unknown bound are subject to some bugs in constant expressions.
const extern int arr[];
constexpr int f(int i) {return arr[i];}
constexpr int arr[] {1, 2, 3};
int main() {constexpr int x = f(2);}
This is spuriously rejected. On the other hand,
extern const int arr[];
constexpr int const* p = arr + 2;
compiles. The standard will presumably incorporate a rule that forbids
array-to-pointer conversions on arrays of unknown bound (unless they are
completed at the point of evaluation, as in the first
example). The proposed changes reflect this idea.
https://reviews.llvm.org/D32372
Files:
include/clang/Basic/DiagnosticASTKinds.td
lib/AST/ExprConstant.cpp
Index: lib/AST/ExprConstant.cpp
===================================================================
--- lib/AST/ExprConstant.cpp
+++ lib/AST/ExprConstant.cpp
@@ -495,7 +495,7 @@
// FIXME: Force the precision of the source value down so we don't
// print digits which are usually useless (we don't really care here if
// we truncate a digit by accident in edge cases). Ideally,
- // APFloat::toString would automatically print the shortest
+ // APFloat::toString would automatically print the shortest
// representation which rounds to the correct value, but it's a bit
// tricky to implement.
unsigned precision =
@@ -720,7 +720,7 @@
private:
OptionalDiagnostic Diag(SourceLocation Loc, diag::kind DiagId,
unsigned ExtraNotes, bool IsCCEDiag) {
-
+
if (EvalStatus.Diag) {
// If we have a prior diagnostic, it will be noting that the expression
// isn't a constant expression. This diagnostic is more important,
@@ -773,7 +773,7 @@
unsigned ExtraNotes = 0) {
return Diag(Loc, DiagId, ExtraNotes, false);
}
-
+
OptionalDiagnostic FFDiag(const Expr *E, diag::kind DiagId
= diag::note_invalid_subexpr_in_const_expr,
unsigned ExtraNotes = 0) {
@@ -2619,10 +2619,23 @@
LastField = nullptr;
if (ObjType->isArrayType()) {
// Next subobject is an array element.
- const ConstantArrayType *CAT = Info.Ctx.getAsConstantArrayType(ObjType);
- assert(CAT && "vla in literal type?");
+ uint64_t actualIndex;
+ const ArrayType *AT = Info.Ctx.getAsArrayType(ObjType); // non-null by assumption
+ if (I == 0) {
+ /* we're dealing with the complete array object, which may have been declared
+ without a bound */
+ actualIndex = Sub.MostDerivedArraySize;
+ assert(Sub.MostDerivedIsArrayElement && "Complete object is an array, but isn't?");
+ }
+ else {
+ /* ... the array must have been given a bound
+ ([dcl.array]/3 for both subarrays and members). */
+ auto CAT = dyn_cast<const ConstantArrayType>(AT);
+ assert(CAT && "vla in literal type?");
+ actualIndex = CAT->getSize().getZExtValue();
+ }
uint64_t Index = Sub.Entries[I].ArrayIndex;
- if (CAT->getSize().ule(Index)) {
+ if (actualIndex <= Index) {
// Note, it should not be possible to form a pointer with a valid
// designator which points more than one past the end of the array.
if (Info.getLangOpts().CPlusPlus11)
@@ -2633,7 +2646,7 @@
return handler.failed();
}
- ObjType = CAT->getElementType();
+ ObjType = AT->getElementType();
// An array object is represented as either an Array APValue or as an
// LValue which refers to a string literal.
@@ -4098,13 +4111,13 @@
if (Info.getLangOpts().CPlusPlus11) {
const FunctionDecl *DiagDecl = Definition ? Definition : Declaration;
-
+
// If this function is not constexpr because it is an inherited
// non-constexpr constructor, diagnose that directly.
auto *CD = dyn_cast<CXXConstructorDecl>(DiagDecl);
if (CD && CD->isInheritingConstructor()) {
auto *Inherited = CD->getInheritedConstructor().getConstructor();
- if (!Inherited->isConstexpr())
+ if (!Inherited->isConstexpr())
DiagDecl = CD = Inherited;
}
@@ -4635,7 +4648,7 @@
return false;
This = &ThisVal;
Args = Args.slice(1);
- } else if (MD && MD->isLambdaStaticInvoker()) {
+ } else if (MD && MD->isLambdaStaticInvoker()) {
// Map the static invoker for the lambda back to the call operator.
// Conveniently, we don't have to slice out the 'this' argument (as is
// being done for the non-static case), since a static member function
@@ -4670,7 +4683,7 @@
FD = LambdaCallOp;
}
-
+
} else
return Error(E);
@@ -5501,7 +5514,7 @@
// Update 'Result' to refer to the data member/field of the closure object
// that represents the '*this' capture.
if (!HandleLValueMember(Info, E, Result,
- Info.CurrentCall->LambdaThisCaptureField))
+ Info.CurrentCall->LambdaThisCaptureField))
return false;
// If we captured '*this' by reference, replace the field with its referent.
if (Info.CurrentCall->LambdaThisCaptureField->getType()
@@ -5636,7 +5649,8 @@
if (SubExpr->isGLValue()) {
if (!evaluateLValue(SubExpr, Result))
return false;
- } else {
+ }
+ else {
Result.set(SubExpr, Info.CurrentCall->Index);
if (!EvaluateInPlace(Info.CurrentCall->createTemporary(SubExpr, false),
Info, Result, SubExpr))
@@ -5646,6 +5660,18 @@
if (const ConstantArrayType *CAT
= Info.Ctx.getAsConstantArrayType(SubExpr->getType()))
Result.addArray(Info, E, CAT);
+ // If the type of the expression is an array of unknown bound, the lvalue must refer
+ // to a declared object. We must check whether its type has been completed.
+ else if (auto decl = Result.Base.dyn_cast<ValueDecl const*>()) {
+ // make sure to consider the completed type.
+ if (auto CAT = Info.Ctx.getAsConstantArrayType(cast<ValueDecl const>(
+ decl->getMostRecentDecl())->getType()))
+ Result.addArray(Info, E, CAT);
+ else {
+ Result.Designator.setInvalid();
+ CCEDiag(SubExpr, diag::note_constexpr_array_unknown_bound_decay);
+ }
+ }
else
Result.Designator.setInvalid();
return true;
@@ -6345,7 +6371,7 @@
if (ClosureClass->isInvalidDecl()) return false;
if (Info.checkingPotentialConstantExpression()) return true;
-
+
const size_t NumFields =
std::distance(ClosureClass->field_begin(), ClosureClass->field_end());
@@ -6364,7 +6390,7 @@
assert(CaptureInitIt != E->capture_init_end());
// Get the initializer for this field
Expr *const CurFieldInit = *CaptureInitIt++;
-
+
// If there is no initializer, either this is a VLA or an error has
// occurred.
if (!CurFieldInit)
@@ -6565,18 +6591,18 @@
// The number of initializers can be less than the number of
// vector elements. For OpenCL, this can be due to nested vector
- // initialization. For GCC compatibility, missing trailing elements
+ // initialization. For GCC compatibility, missing trailing elements
// should be initialized with zeroes.
unsigned CountInits = 0, CountElts = 0;
while (CountElts < NumElements) {
// Handle nested vector initialization.
- if (CountInits < NumInits
+ if (CountInits < NumInits
&& E->getInit(CountInits)->getType()->isVectorType()) {
APValue v;
if (!EvaluateVector(E->getInit(CountInits), v, Info))
return Error(E);
unsigned vlen = v.getVectorLength();
- for (unsigned j = 0; j < vlen; j++)
+ for (unsigned j = 0; j < vlen; j++)
Elements.push_back(v.getVectorElt(j));
CountElts += vlen;
} else if (EltTy->isIntegerType()) {
@@ -6852,7 +6878,7 @@
}
bool Success(const llvm::APInt &I, const Expr *E, APValue &Result) {
- assert(E->getType()->isIntegralOrEnumerationType() &&
+ assert(E->getType()->isIntegralOrEnumerationType() &&
"Invalid evaluation result.");
assert(I.getBitWidth() == Info.Ctx.getIntWidth(E->getType()) &&
"Invalid evaluation result.");
@@ -6866,7 +6892,7 @@
}
bool Success(uint64_t Value, const Expr *E, APValue &Result) {
- assert(E->getType()->isIntegralOrEnumerationType() &&
+ assert(E->getType()->isIntegralOrEnumerationType() &&
"Invalid evaluation result.");
Result = APValue(Info.Ctx.MakeIntValue(Value, E->getType()));
return true;
@@ -6942,7 +6968,7 @@
}
return Success(Info.ArrayInitIndex, E);
}
-
+
// Note, GNU defines __null as an integer, not a pointer.
bool VisitGNUNullExpr(const GNUNullExpr *E) {
return ZeroInitialization(E);
@@ -8096,12 +8122,12 @@
Result = RHSResult.Val;
return true;
}
-
+
if (E->isLogicalOp()) {
bool lhsResult, rhsResult;
bool LHSIsOK = HandleConversionToBool(LHSResult.Val, lhsResult);
bool RHSIsOK = HandleConversionToBool(RHSResult.Val, rhsResult);
-
+
if (LHSIsOK) {
if (RHSIsOK) {
if (E->getOpcode() == BO_LOr)
@@ -8117,34 +8143,34 @@
return Success(rhsResult, E, Result);
}
}
-
+
return false;
}
-
+
assert(E->getLHS()->getType()->isIntegralOrEnumerationType() &&
E->getRHS()->getType()->isIntegralOrEnumerationType());
-
+
if (LHSResult.Failed || RHSResult.Failed)
return false;
-
+
const APValue &LHSVal = LHSResult.Val;
const APValue &RHSVal = RHSResult.Val;
-
+
// Handle cases like (unsigned long)&a + 4.
if (E->isAdditiveOp() && LHSVal.isLValue() && RHSVal.isInt()) {
Result = LHSVal;
addOrSubLValueAsInteger(Result, RHSVal.getInt(), E->getOpcode() == BO_Sub);
return true;
}
-
+
// Handle cases like 4 + (unsigned long)&a
if (E->getOpcode() == BO_Add &&
RHSVal.isLValue() && LHSVal.isInt()) {
Result = RHSVal;
addOrSubLValueAsInteger(Result, LHSVal.getInt(), /*IsSub*/false);
return true;
}
-
+
if (E->getOpcode() == BO_Sub && LHSVal.isLValue() && RHSVal.isLValue()) {
// Handle (intptr_t)&&A - (intptr_t)&&B.
if (!LHSVal.getLValueOffset().isZero() ||
@@ -8183,7 +8209,7 @@
void DataRecursiveIntBinOpEvaluator::process(EvalResult &Result) {
Job &job = Queue.back();
-
+
switch (job.Kind) {
case Job::AnyExprKind: {
if (const BinaryOperator *Bop = dyn_cast<BinaryOperator>(job.E)) {
@@ -8193,12 +8219,12 @@
return;
}
}
-
+
EvaluateExpr(job.E, Result);
Queue.pop_back();
return;
}
-
+
case Job::BinOpKind: {
const BinaryOperator *Bop = cast<BinaryOperator>(job.E);
bool SuppressRHSDiags = false;
@@ -8213,7 +8239,7 @@
enqueue(Bop->getRHS());
return;
}
-
+
case Job::BinOpVisitedLHSKind: {
const BinaryOperator *Bop = cast<BinaryOperator>(job.E);
EvalResult RHS;
@@ -8223,7 +8249,7 @@
return;
}
}
-
+
llvm_unreachable("Invalid Job::Kind!");
}
@@ -8735,7 +8761,7 @@
const RecordType *BaseRT = CurrentType->getAs<RecordType>();
if (!BaseRT)
return Error(OOE);
-
+
// Add the offset to the base.
Result += RL.getBaseClassOffset(cast<CXXRecordDecl>(BaseRT->getDecl()));
break;
@@ -9929,7 +9955,7 @@
IsConst = false;
return true;
}
-
+
// FIXME: Evaluating values of large array and record types can cause
// performance problems. Only do so in C++11 for now.
if (Exp->isRValue() && (Exp->getType()->isArrayType() ||
@@ -9951,7 +9977,7 @@
bool IsConst;
if (FastEvaluateAsRValue(this, Result, Ctx, IsConst))
return IsConst;
-
+
EvalInfo Info(Ctx, Result, EvalInfo::EM_IgnoreSideEffects);
return ::EvaluateAsRValue(Info, this, Result.Val);
}
Index: include/clang/Basic/DiagnosticASTKinds.td
===================================================================
--- include/clang/Basic/DiagnosticASTKinds.td
+++ include/clang/Basic/DiagnosticASTKinds.td
@@ -154,12 +154,14 @@
def note_constexpr_baa_value_insufficient_alignment : Note<
"value of the aligned pointer (%0) is not a multiple of the asserted %1 "
"%plural{1:byte|:bytes}1">;
+def note_constexpr_array_unknown_bound_decay : Note<
+ "cannot perform array to pointer conversion on array of unknown bound">;
def warn_integer_constant_overflow : Warning<
"overflow in expression; result is %0 with type %1">,
InGroup<DiagGroup<"integer-overflow">>;
-// This is a temporary diagnostic, and shall be removed once our
+// This is a temporary diagnostic, and shall be removed once our
// implementation is complete, and like the preceding constexpr notes belongs
// in Sema.
def note_unimplemented_constexpr_lambda_feature_ast : Note<
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