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[Sema] Note when we encounter a problem in ExprConstant. 

Currently, the constexpr evaluator is very conservative about unmodeled
side-effects when we're evaluating an expression in a mode that allows
such side-effects.

This patch makes us note when we might have actually encountered an
unmodeled side-effect, which allows us to be more accurate when we know
an unmodeled side-effect couldn't have occurred.

This patch has been split into two commits; this one primarily
introduces the bits necessary to track whether we might have potentially
hit such a side-effect. The one that actually does the tracking (which
boils down to more or less a rename of keepEvaluatingAfterFailure to
noteFailure) is coming soon.

Differential Revision: http://reviews.llvm.org/D18540

llvm-svn: 270781
This commit is contained in:
George Burgess IV 2016-05-25 22:31:54 +00:00
parent 1b356bf898
commit 8c892b556f
3 changed files with 220 additions and 37 deletions
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139
clang/lib/AST/ExprConstant.cpp
View File

@ -478,6 +478,9 @@ namespace {
/// fold (not just why it's not strictly a constant expression)?
bool HasFoldFailureDiagnostic;
/// \brief Whether or not we're currently speculatively evaluating.
bool IsSpeculativelyEvaluating;
enum EvaluationMode {
/// Evaluate as a constant expression. Stop if we find that the expression
/// is not a constant expression.
@ -542,7 +545,8 @@ namespace {
BottomFrame(*this, SourceLocation(), nullptr, nullptr, nullptr),
EvaluatingDecl((const ValueDecl *)nullptr),
EvaluatingDeclValue(nullptr), HasActiveDiagnostic(false),
HasFoldFailureDiagnostic(false), EvalMode(Mode) {}
HasFoldFailureDiagnostic(false), IsSpeculativelyEvaluating(false),
EvalMode(Mode) {}
void setEvaluatingDecl(APValue::LValueBase Base, APValue &Value) {
EvaluatingDecl = Base;
@ -764,6 +768,29 @@ namespace {
llvm_unreachable("Missed EvalMode case");
}
/// Notes that we failed to evaluate an expression that other expressions
/// directly depend on, and determine if we should keep evaluating. This
/// should only be called if we actually intend to keep evaluating.
///
/// Call noteSideEffect() instead if we may be able to ignore the value that
/// we failed to evaluate, e.g. if we failed to evaluate Foo() in:
///
/// (Foo(), 1) // use noteSideEffect
/// (Foo() || true) // use noteSideEffect
/// Foo() + 1 // use noteFailure
LLVM_ATTRIBUTE_UNUSED_RESULT bool noteFailure() {
// Failure when evaluating some expression often means there is some
// subexpression whose evaluation was skipped. Therefore, (because we
// don't track whether we skipped an expression when unwinding after an
// evaluation failure) every evaluation failure that bubbles up from a
// subexpression implies that a side-effect has potentially happened. We
// skip setting the HasSideEffects flag to true until we decide to
// continue evaluating after that point, which happens here.
bool KeepGoing = keepEvaluatingAfterFailure();
EvalStatus.HasSideEffects |= KeepGoing;
return KeepGoing;
}
bool allowInvalidBaseExpr() const {
return EvalMode == EM_DesignatorFold;
}
@ -812,24 +839,52 @@ namespace {
~FoldOffsetRAII() { Info.EvalMode = OldMode; }
};
/// RAII object used to suppress diagnostics and side-effects from a
/// speculative evaluation.
/// RAII object used to optionally suppress diagnostics and side-effects from
/// a speculative evaluation.
class SpeculativeEvaluationRAII {
EvalInfo &Info;
/// Pair of EvalInfo, and a bit that stores whether or not we were
/// speculatively evaluating when we created this RAII.
llvm::PointerIntPair<EvalInfo *, 1, bool> InfoAndOldSpecEval;
Expr::EvalStatus Old;
void moveFromAndCancel(SpeculativeEvaluationRAII &&Other) {
InfoAndOldSpecEval = Other.InfoAndOldSpecEval;
Old = Other.Old;
Other.InfoAndOldSpecEval.setPointer(nullptr);
}
void maybeRestoreState() {
EvalInfo *Info = InfoAndOldSpecEval.getPointer();
if (!Info)
return;
Info->EvalStatus = Old;
Info->IsSpeculativelyEvaluating = InfoAndOldSpecEval.getInt();
}
public:
SpeculativeEvaluationRAII(EvalInfo &Info,
SmallVectorImpl<PartialDiagnosticAt> *NewDiag = nullptr)
: Info(Info), Old(Info.EvalStatus) {
SpeculativeEvaluationRAII() = default;
SpeculativeEvaluationRAII(
EvalInfo &Info, SmallVectorImpl<PartialDiagnosticAt> *NewDiag = nullptr)
: InfoAndOldSpecEval(&Info, Info.IsSpeculativelyEvaluating),
Old(Info.EvalStatus) {
Info.EvalStatus.Diag = NewDiag;
// If we're speculatively evaluating, we may have skipped over some
// evaluations and missed out a side effect.
Info.EvalStatus.HasSideEffects = true;
Info.IsSpeculativelyEvaluating = true;
}
~SpeculativeEvaluationRAII() {
Info.EvalStatus = Old;
SpeculativeEvaluationRAII(const SpeculativeEvaluationRAII &Other) = delete;
SpeculativeEvaluationRAII(SpeculativeEvaluationRAII &&Other) {
moveFromAndCancel(std::move(Other));
}
SpeculativeEvaluationRAII &operator=(SpeculativeEvaluationRAII &&Other) {
maybeRestoreState();
moveFromAndCancel(std::move(Other));
return *this;
}
~SpeculativeEvaluationRAII() { maybeRestoreState(); }
};
/// RAII object wrapping a full-expression or block scope, and handling
@ -2789,12 +2844,13 @@ static CompleteObject findCompleteObject(EvalInfo &Info, const Expr *E,
}
// In C++1y, we can't safely access any mutable state when we might be
// evaluating after an unmodeled side effect or an evaluation failure.
// evaluating after an unmodeled side effect.
//
// FIXME: Not all local state is mutable. Allow local constant subobjects
// to be read here (but take care with 'mutable' fields).
if (Frame && Info.getLangOpts().CPlusPlus14 &&
(Info.EvalStatus.HasSideEffects || Info.keepEvaluatingAfterFailure()))
if ((Frame && Info.getLangOpts().CPlusPlus14 &&
Info.EvalStatus.HasSideEffects) ||
(AK != AK_Read && Info.IsSpeculativelyEvaluating))
return CompleteObject();
return CompleteObject(BaseVal, BaseType);
@ -4049,14 +4105,16 @@ private:
assert(Info.checkingPotentialConstantExpression());
// Speculatively evaluate both arms.
{
SmallVector<PartialDiagnosticAt, 8> Diag;
{
SpeculativeEvaluationRAII Speculate(Info, &Diag);
StmtVisitorTy::Visit(E->getFalseExpr());
if (Diag.empty())
return;
}
{
SpeculativeEvaluationRAII Speculate(Info, &Diag);
Diag.clear();
StmtVisitorTy::Visit(E->getTrueExpr());
if (Diag.empty())
@ -4071,7 +4129,7 @@ private:
bool HandleConditionalOperator(const ConditionalOperator *E) {
bool BoolResult;
if (!EvaluateAsBooleanCondition(E->getCond(), BoolResult, Info)) {
if (Info.checkingPotentialConstantExpression())
if (Info.checkingPotentialConstantExpression() && Info.noteFailure())
CheckPotentialConstantConditional(E);
return false;
}
@ -7027,23 +7085,14 @@ class DataRecursiveIntBinOpEvaluator {
Job() = default;
Job(Job &&J)
: E(J.E), LHSResult(J.LHSResult), Kind(J.Kind),
StoredInfo(J.StoredInfo), OldEvalStatus(J.OldEvalStatus) {
J.StoredInfo = nullptr;
}
SpecEvalRAII(std::move(J.SpecEvalRAII)) {}
void startSpeculativeEval(EvalInfo &Info) {
OldEvalStatus = Info.EvalStatus;
Info.EvalStatus.Diag = nullptr;
StoredInfo = &Info;
}
~Job() {
if (StoredInfo) {
StoredInfo->EvalStatus = OldEvalStatus;
}
SpecEvalRAII = SpeculativeEvaluationRAII(Info);
}
private:
EvalInfo *StoredInfo = nullptr; // non-null if status changed.
Expr::EvalStatus OldEvalStatus;
SpeculativeEvaluationRAII SpecEvalRAII;
};
SmallVector<Job, 16> Queue;
@ -7145,7 +7194,7 @@ bool DataRecursiveIntBinOpEvaluator::
LHSResult.Failed = true;
// Since we weren't able to evaluate the left hand side, it
// must have had side effects.
// might have had side effects.
if (!Info.noteSideEffect())
return false;
@ -7313,10 +7362,34 @@ void DataRecursiveIntBinOpEvaluator::process(EvalResult &Result) {
llvm_unreachable("Invalid Job::Kind!");
}
namespace {
/// Used when we determine that we should fail, but can keep evaluating prior to
/// noting that we had a failure.
class DelayedNoteFailureRAII {
EvalInfo &Info;
bool NoteFailure;
public:
DelayedNoteFailureRAII(EvalInfo &Info, bool NoteFailure = true)
: Info(Info), NoteFailure(NoteFailure) {}
~DelayedNoteFailureRAII() {
if (NoteFailure) {
bool ContinueAfterFailure = Info.noteFailure();
(void)ContinueAfterFailure;
assert(ContinueAfterFailure &&
"Shouldn't have kept evaluating on failure.");
}
}
};
}
bool IntExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) {
// We don't call noteFailure immediately because the assignment happens after
// we evaluate LHS and RHS.
if (!Info.keepEvaluatingAfterFailure() && E->isAssignmentOp())
return Error(E);
DelayedNoteFailureRAII MaybeNoteFailureLater(Info, E->isAssignmentOp());
if (DataRecursiveIntBinOpEvaluator::shouldEnqueue(E))
return DataRecursiveIntBinOpEvaluator(*this, Result).Traverse(E);
@ -7638,7 +7711,7 @@ bool IntExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) {
MemberPtr LHSValue, RHSValue;
bool LHSOK = EvaluateMemberPointer(E->getLHS(), LHSValue, Info);
if (!LHSOK && Info.keepEvaluatingAfterFailure())
if (!LHSOK && !Info.keepEvaluatingAfterFailure())
return false;
if (!EvaluateMemberPointer(E->getRHS(), RHSValue, Info) || !LHSOK)

99
clang/test/SemaCXX/builtin-object-size-cxx14.cpp Normal file
View File

@ -0,0 +1,99 @@
// RUN: %clang_cc1 -fsyntax-only -verify -std=c++14 %s
namespace basic {
// Ensuring that __bos can be used in constexpr functions without anything
// sketchy going on...
constexpr int bos0() {
int k = 5;
char cs[10] = {};
return __builtin_object_size(&cs[k], 0);
}
constexpr int bos1() {
int k = 5;
char cs[10] = {};
return __builtin_object_size(&cs[k], 1);
}
constexpr int bos2() {
int k = 5;
char cs[10] = {};
return __builtin_object_size(&cs[k], 2);
}
constexpr int bos3() {
int k = 5;
char cs[10] = {};
return __builtin_object_size(&cs[k], 3);
}
static_assert(bos0() == sizeof(char) * 5, "");
static_assert(bos1() == sizeof(char) * 5, "");
static_assert(bos2() == sizeof(char) * 5, "");
static_assert(bos3() == sizeof(char) * 5, "");
}
namespace in_enable_if {
// The code that prompted these changes was __bos in enable_if
void copy5CharsInto(char *buf) // expected-note{{candidate}}
__attribute__((enable_if(__builtin_object_size(buf, 0) != -1 &&
__builtin_object_size(buf, 0) > 5,
"")));
// We use different EvalModes for __bos with type 0 versus 1. Ensure 1 works,
// too...
void copy5CharsIntoStrict(char *buf) // expected-note{{candidate}}
__attribute__((enable_if(__builtin_object_size(buf, 1) != -1 &&
__builtin_object_size(buf, 1) > 5,
"")));
struct LargeStruct {
int pad;
char buf[6];
int pad2;
};
struct SmallStruct {
int pad;
char buf[5];
int pad2;
};
void noWriteToBuf() {
char buf[6];
copy5CharsInto(buf);
LargeStruct large;
copy5CharsIntoStrict(large.buf);
}
void initTheBuf() {
char buf[6] = {};
copy5CharsInto(buf);
LargeStruct large = {0, {}, 0};
copy5CharsIntoStrict(large.buf);
}
int getI();
void initTheBufWithALoop() {
char buf[6] = {};
for (unsigned I = getI(); I != sizeof(buf); ++I)
buf[I] = I;
copy5CharsInto(buf);
LargeStruct large;
for (unsigned I = getI(); I != sizeof(buf); ++I)
large.buf[I] = I;
copy5CharsIntoStrict(large.buf);
}
void tooSmallBuf() {
char buf[5];
copy5CharsInto(buf); // expected-error{{no matching function for call}}
SmallStruct small;
copy5CharsIntoStrict(small.buf); // expected-error{{no matching function for call}}
}
}

19
clang/test/SemaCXX/constant-expression-cxx1y.cpp
View File

@ -179,12 +179,10 @@ namespace string_assign {
static_assert(!test1(100), "");
static_assert(!test1(101), ""); // expected-error {{constant expression}} expected-note {{in call to 'test1(101)'}}
// FIXME: We should be able to reject this before it's called
constexpr void f() {
constexpr void f() { // expected-error{{constexpr function never produces a constant expression}} expected-note@+2{{assignment to dereferenced one-past-the-end pointer is not allowed in a constant expression}}
char foo[10] = { "z" }; // expected-note {{here}}
foo[10] = 'x'; // expected-warning {{past the end}} expected-note {{assignment to dereferenced one-past-the-end pointer}}
foo[10] = 'x'; // expected-warning {{past the end}}
}
constexpr int k = (f(), 0); // expected-error {{constant expression}} expected-note {{in call}}
}
namespace array_resize {
@ -938,3 +936,16 @@ namespace EmptyClass {
constexpr int testb = f(e2, 3); // expected-error {{constant expression}} expected-note {{in call}}
constexpr int testc = f(e3, 3);
}
namespace SpeculativeEvalWrites {
// Ensure that we don't try to speculatively evaluate writes.
constexpr int f() {
int i = 0;
int a = 0;
// __builtin_object_size speculatively evaluates its first argument.
__builtin_object_size((i = 1, &a), 0);
return i;
}
static_assert(!f(), "");
}