Author: rsmith
Date: Mon Aug 28 18:52:13 2017
New Revision: 311970
URL: http://llvm.org/viewvc/llvm-project?rev=311970&view=rev
Log:
Improve constant expression evaluation of arrays of unknown bound.
The standard is not clear on how these are supposed to be handled, so we
conservatively treat as non-constant any cases whose value is unknown or whose
evaluation might result in undefined behavior.
Modified:
cfe/trunk/include/clang/Basic/DiagnosticASTKinds.td
cfe/trunk/include/clang/Basic/DiagnosticIDs.h
cfe/trunk/lib/AST/ExprConstant.cpp
cfe/trunk/test/SemaCXX/constant-expression-cxx11.cpp
Modified: cfe/trunk/include/clang/Basic/DiagnosticASTKinds.td
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticASTKinds.td?rev=311970&r1=311969&r2=311970&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticASTKinds.td (original)
+++ cfe/trunk/include/clang/Basic/DiagnosticASTKinds.td Mon Aug 28 18:52:13 2017
@@ -127,6 +127,10 @@ def note_constexpr_access_null : Note<
def note_constexpr_access_past_end : Note<
"%select{read of|assignment to|increment of|decrement of}0 "
"dereferenced one-past-the-end pointer is not allowed in a constant
expression">;
+def note_constexpr_access_unsized_array : Note<
+ "%select{read of|assignment to|increment of|decrement of}0 "
+ "pointer to element of array without known bound "
+ "is not allowed in a constant expression">;
def note_constexpr_access_inactive_union_member : Note<
"%select{read of|assignment to|increment of|decrement of}0 "
"member %1 of union with %select{active member %3|no active member}2 "
@@ -154,6 +158,11 @@ def note_constexpr_baa_insufficient_alig
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_unsupported_unsized_array : Note<
+ "array-to-pointer decay of array member without known bound is not
supported">;
+def note_constexpr_unsized_array_indexed : Note<
+ "indexing of array without known bound is not allowed "
+ "in a constant expression">;
def warn_integer_constant_overflow : Warning<
"overflow in expression; result is %0 with type %1">,
Modified: cfe/trunk/include/clang/Basic/DiagnosticIDs.h
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticIDs.h?rev=311970&r1=311969&r2=311970&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticIDs.h (original)
+++ cfe/trunk/include/clang/Basic/DiagnosticIDs.h Mon Aug 28 18:52:13 2017
@@ -34,7 +34,7 @@ namespace clang {
DIAG_SIZE_SERIALIZATION = 120,
DIAG_SIZE_LEX = 400,
DIAG_SIZE_PARSE = 500,
- DIAG_SIZE_AST = 110,
+ DIAG_SIZE_AST = 150,
DIAG_SIZE_COMMENT = 100,
DIAG_SIZE_SEMA = 3500,
DIAG_SIZE_ANALYSIS = 100
Modified: cfe/trunk/lib/AST/ExprConstant.cpp
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/ExprConstant.cpp?rev=311970&r1=311969&r2=311970&view=diff
==============================================================================
--- cfe/trunk/lib/AST/ExprConstant.cpp (original)
+++ cfe/trunk/lib/AST/ExprConstant.cpp Mon Aug 28 18:52:13 2017
@@ -141,6 +141,12 @@ namespace {
return E && E->getType()->isPointerType() && tryUnwrapAllocSizeCall(E);
}
+ /// The bound to claim that an array of unknown bound has.
+ /// The value in MostDerivedArraySize is undefined in this case. So, set it
+ /// to an arbitrary value that's likely to loudly break things if it's used.
+ static const uint64_t AssumedSizeForUnsizedArray =
+ std::numeric_limits<uint64_t>::max() / 2;
+
/// Determines if an LValue with the given LValueBase will have an unsized
/// array in its designator.
/// Find the path length and type of the most-derived subobject in the given
@@ -148,7 +154,8 @@ namespace {
static unsigned
findMostDerivedSubobject(ASTContext &Ctx, APValue::LValueBase Base,
ArrayRef<APValue::LValuePathEntry> Path,
- uint64_t &ArraySize, QualType &Type, bool &IsArray)
{
+ uint64_t &ArraySize, QualType &Type, bool &IsArray,
+ bool &FirstEntryIsUnsizedArray) {
// This only accepts LValueBases from APValues, and APValues don't support
// arrays that lack size info.
assert(!isBaseAnAllocSizeCall(Base) &&
@@ -158,12 +165,18 @@ namespace {
for (unsigned I = 0, N = Path.size(); I != N; ++I) {
if (Type->isArrayType()) {
- const ConstantArrayType *CAT =
- cast<ConstantArrayType>(Ctx.getAsArrayType(Type));
- Type = CAT->getElementType();
- ArraySize = CAT->getSize().getZExtValue();
+ const ArrayType *AT = Ctx.getAsArrayType(Type);
+ Type = AT->getElementType();
MostDerivedLength = I + 1;
IsArray = true;
+
+ if (auto *CAT = dyn_cast<ConstantArrayType>(AT)) {
+ ArraySize = CAT->getSize().getZExtValue();
+ } else {
+ assert(I == 0 && "unexpected unsized array designator");
+ FirstEntryIsUnsizedArray = true;
+ ArraySize = AssumedSizeForUnsizedArray;
+ }
} else if (Type->isAnyComplexType()) {
const ComplexType *CT = Type->castAs<ComplexType>();
Type = CT->getElementType();
@@ -246,10 +259,12 @@ namespace {
Entries.insert(Entries.end(), VEntries.begin(), VEntries.end());
if (V.getLValueBase()) {
bool IsArray = false;
+ bool FirstIsUnsizedArray = false;
MostDerivedPathLength = findMostDerivedSubobject(
Ctx, V.getLValueBase(), V.getLValuePath(), MostDerivedArraySize,
- MostDerivedType, IsArray);
+ MostDerivedType, IsArray, FirstIsUnsizedArray);
MostDerivedIsArrayElement = IsArray;
+ FirstEntryIsAnUnsizedArray = FirstIsUnsizedArray;
}
}
}
@@ -318,7 +333,7 @@ namespace {
// The value in MostDerivedArraySize is undefined in this case. So, set
it
// to an arbitrary value that's likely to loudly break things if it's
// used.
- MostDerivedArraySize = std::numeric_limits<uint64_t>::max() / 2;
+ MostDerivedArraySize = AssumedSizeForUnsizedArray;
MostDerivedPathLength = Entries.size();
}
/// Update this designator to refer to the given base or member of this
@@ -350,6 +365,7 @@ namespace {
MostDerivedArraySize = 2;
MostDerivedPathLength = Entries.size();
}
+ void diagnoseUnsizedArrayPointerArithmetic(EvalInfo &Info, const Expr *E);
void diagnosePointerArithmetic(EvalInfo &Info, const Expr *E,
const APSInt &N);
/// Add N to the address of this subobject.
@@ -357,6 +373,7 @@ namespace {
if (Invalid || !N) return;
uint64_t TruncatedN = N.extOrTrunc(64).getZExtValue();
if (isMostDerivedAnUnsizedArray()) {
+ diagnoseUnsizedArrayPointerArithmetic(Info, E);
// Can't verify -- trust that the user is doing the right thing (or if
// not, trust that the caller will catch the bad behavior).
// FIXME: Should we reject if this overflows, at least?
@@ -1068,9 +1085,19 @@ bool SubobjectDesignator::checkSubobject
setInvalid();
return false;
}
+ // Note, we do not diagnose if isMostDerivedAnUnsizedArray(), because there
+ // must actually be at least one array element; even a VLA cannot have a
+ // bound of zero. And if our index is nonzero, we already had a CCEDiag.
return true;
}
+void SubobjectDesignator::diagnoseUnsizedArrayPointerArithmetic(EvalInfo &Info,
+ const Expr *E)
{
+ Info.CCEDiag(E, diag::note_constexpr_unsized_array_indexed);
+ // Do not set the designator as invalid: we can represent this situation,
+ // and correct handling of __builtin_object_size requires us to do so.
+}
+
void SubobjectDesignator::diagnosePointerArithmetic(EvalInfo &Info,
const Expr *E,
const APSInt &N) {
@@ -1214,8 +1241,6 @@ namespace {
IsNullPtr);
else {
assert(!InvalidBase && "APValues can't handle invalid LValue bases");
- assert(!Designator.FirstEntryIsAnUnsizedArray &&
- "Unsized array with a valid base?");
V = APValue(Base, Offset, Designator.Entries,
Designator.IsOnePastTheEnd, CallIndex, IsNullPtr);
}
@@ -1288,10 +1313,14 @@ namespace {
if (checkSubobject(Info, E, isa<FieldDecl>(D) ? CSK_Field : CSK_Base))
Designator.addDeclUnchecked(D, Virtual);
}
- void addUnsizedArray(EvalInfo &Info, QualType ElemTy) {
- assert(Designator.Entries.empty() && getType(Base)->isPointerType());
- assert(isBaseAnAllocSizeCall(Base) &&
- "Only alloc_size bases can have unsized arrays");
+ void addUnsizedArray(EvalInfo &Info, const Expr *E, QualType ElemTy) {
+ if (!Designator.Entries.empty()) {
+ Info.CCEDiag(E, diag::note_constexpr_unsupported_unsized_array);
+ Designator.setInvalid();
+ return;
+ }
+
+ assert(getType(Base)->isPointerType() || getType(Base)->isArrayType());
Designator.FirstEntryIsAnUnsizedArray = true;
Designator.addUnsizedArrayUnchecked(ElemTy);
}
@@ -2598,10 +2627,12 @@ findSubobject(EvalInfo &Info, const Expr
if (Sub.Invalid)
// A diagnostic will have already been produced.
return handler.failed();
- if (Sub.isOnePastTheEnd()) {
+ if (Sub.isOnePastTheEnd() || Sub.isMostDerivedAnUnsizedArray()) {
if (Info.getLangOpts().CPlusPlus11)
- Info.FFDiag(E, diag::note_constexpr_access_past_end)
- << handler.AccessKind;
+ Info.FFDiag(E, Sub.isOnePastTheEnd()
+ ? diag::note_constexpr_access_past_end
+ : diag::note_constexpr_access_unsized_array)
+ << handler.AccessKind;
else
Info.FFDiag(E);
return handler.failed();
@@ -5460,7 +5491,7 @@ static bool evaluateLValueAsAllocSize(Ev
Result.setInvalid(E);
QualType Pointee = E->getType()->castAs<PointerType>()->getPointeeType();
- Result.addUnsizedArray(Info, Pointee);
+ Result.addUnsizedArray(Info, E, Pointee);
return true;
}
@@ -5670,7 +5701,8 @@ bool PointerExprEvaluator::VisitCastExpr
return true;
}
}
- case CK_ArrayToPointerDecay:
+
+ case CK_ArrayToPointerDecay: {
if (SubExpr->isGLValue()) {
if (!evaluateLValue(SubExpr, Result))
return false;
@@ -5681,12 +5713,13 @@ bool PointerExprEvaluator::VisitCastExpr
return false;
}
// The result is a pointer to the first element of the array.
- if (const ConstantArrayType *CAT
- = Info.Ctx.getAsConstantArrayType(SubExpr->getType()))
+ auto *AT = Info.Ctx.getAsArrayType(SubExpr->getType());
+ if (auto *CAT = dyn_cast<ConstantArrayType>(AT))
Result.addArray(Info, E, CAT);
else
- Result.Designator.setInvalid();
+ Result.addUnsizedArray(Info, E, AT->getElementType());
return true;
+ }
case CK_FunctionToPointerDecay:
return evaluateLValue(SubExpr, Result);
@@ -5753,7 +5786,7 @@ bool PointerExprEvaluator::visitNonBuilt
Result.setInvalid(E);
QualType PointeeTy = E->getType()->castAs<PointerType>()->getPointeeType();
- Result.addUnsizedArray(Info, PointeeTy);
+ Result.addUnsizedArray(Info, E, PointeeTy);
return true;
}
@@ -7314,7 +7347,8 @@ static const Expr *ignorePointerCastsAnd
/// Please note: this function is specialized for how __builtin_object_size
/// views "objects".
///
-/// If this encounters an invalid RecordDecl, it will always return true.
+/// If this encounters an invalid RecordDecl or otherwise cannot determine the
+/// correct result, it will always return true.
static bool isDesignatorAtObjectEnd(const ASTContext &Ctx, const LValue &LVal)
{
assert(!LVal.Designator.Invalid);
@@ -7345,9 +7379,8 @@ static bool isDesignatorAtObjectEnd(cons
unsigned I = 0;
QualType BaseType = getType(Base);
if (LVal.Designator.FirstEntryIsAnUnsizedArray) {
- assert(isBaseAnAllocSizeCall(Base) &&
- "Unsized array in non-alloc_size call?");
- // If this is an alloc_size base, we should ignore the initial array index
+ // If we don't know the array bound, conservatively assume we're looking at
+ // the final array element.
++I;
BaseType = BaseType->castAs<PointerType>()->getPointeeType();
}
Modified: cfe/trunk/test/SemaCXX/constant-expression-cxx11.cpp
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/constant-expression-cxx11.cpp?rev=311970&r1=311969&r2=311970&view=diff
==============================================================================
--- cfe/trunk/test/SemaCXX/constant-expression-cxx11.cpp (original)
+++ cfe/trunk/test/SemaCXX/constant-expression-cxx11.cpp Mon Aug 28 18:52:13
2017
@@ -604,6 +604,34 @@ static_assert(NATDCArray{}[1][1].n == 0,
}
+// FIXME: The rules in this case are unclear, but we conservatively choose to
+// reject any cases where pointer arithmetic is not statically known to be
+// valid.
+namespace ArrayOfUnknownBound {
+ extern int arr[];
+ constexpr int *a = arr;
+ constexpr int *b = &arr[0];
+ static_assert(a == b, "");
+ constexpr int *c = &arr[1]; // expected-error {{constant}} expected-note
{{indexing of array without known bound}}
+ constexpr int *d = &a[1]; // expected-error {{constant}} expected-note
{{indexing of array without known bound}}
+ constexpr int *e = a + 1; // expected-error {{constant}} expected-note
{{indexing of array without known bound}}
+
+ struct X {
+ int a;
+ int b[]; // expected-warning {{C99}}
+ };
+ extern X x;
+ constexpr int *xb = x.b; // expected-error {{constant}} expected-note {{not
supported}}
+
+ struct Y { int a; };
+ extern Y yarr[];
+ constexpr Y *p = yarr;
+ constexpr int *q = &p->a;
+
+ extern const int carr[]; // expected-note {{here}}
+ constexpr int n = carr[0]; // expected-error {{constant}} expected-note
{{non-constexpr variable}}
+}
+
namespace DependentValues {
struct I { int n; typedef I V[10]; };
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