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When evaluating a __builtin_constant_p conditional, always enter 

constant-folding mode regardless of the original evaluation mode.

In order for this to be correct, we need to track whether we're checking
for a potential constant expression or checking for undefined behavior
separately from the evaluation mode enum, since we don't want to clobber
those states when entering constant-folding mode.

llvm-svn: 371557
This commit is contained in:
Richard Smith 2019-09-10 21:24:09 +00:00
parent 1e1db80048
commit 045b2270ce
2 changed files with 45 additions and 64 deletions
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106
clang/lib/AST/ExprConstant.cpp
View File

@ -794,30 +794,21 @@ namespace {
/// constant value.
bool InConstantContext;
/// Whether we're checking that an expression is a potential constant
/// expression. If so, do not fail on constructs that could become constant
/// later on (such as a use of an undefined global).
bool CheckingPotentialConstantExpression = false;
/// Whether we're checking for an expression that has undefined behavior.
/// If so, we will produce warnings if we encounter an operation that is
/// always undefined.
bool CheckingForUndefinedBehavior = false;
enum EvaluationMode {
/// Evaluate as a constant expression. Stop if we find that the expression
/// is not a constant expression.
EM_ConstantExpression,
/// Evaluate as a potential constant expression. Keep going if we hit a
/// construct that we can't evaluate yet (because we don't yet know the
/// value of something) but stop if we hit something that could never be
/// a constant expression.
EM_PotentialConstantExpression,
/// Fold the expression to a constant. Stop if we hit a side-effect that
/// we can't model.
EM_ConstantFold,
/// Evaluate the expression looking for integer overflow and similar
/// issues. Don't worry about side-effects, and try to visit all
/// subexpressions.
EM_EvaluateForOverflow,
/// Evaluate in any way we know how. Don't worry about side-effects that
/// can't be modeled.
EM_IgnoreSideEffects,
/// Evaluate as a constant expression. Stop if we find that the expression
/// is not a constant expression. Some expressions can be retried in the
/// optimizer if we don't constant fold them here, but in an unevaluated
@ -825,27 +816,25 @@ namespace {
/// gets a chance to look at it.
EM_ConstantExpressionUnevaluated,
/// Evaluate as a potential constant expression. Keep going if we hit a
/// construct that we can't evaluate yet (because we don't yet know the
/// value of something) but stop if we hit something that could never be
/// a constant expression. Some expressions can be retried in the
/// optimizer if we don't constant fold them here, but in an unevaluated
/// context we try to fold them immediately since the optimizer never
/// gets a chance to look at it.
EM_PotentialConstantExpressionUnevaluated,
/// Fold the expression to a constant. Stop if we hit a side-effect that
/// we can't model.
EM_ConstantFold,
/// Evaluate in any way we know how. Don't worry about side-effects that
/// can't be modeled.
EM_IgnoreSideEffects,
} EvalMode;
/// Are we checking whether the expression is a potential constant
/// expression?
bool checkingPotentialConstantExpression() const {
return EvalMode == EM_PotentialConstantExpression ||
EvalMode == EM_PotentialConstantExpressionUnevaluated;
return CheckingPotentialConstantExpression;
}
/// Are we checking an expression for overflow?
// FIXME: We should check for any kind of undefined or suspicious behavior
// in such constructs, not just overflow.
bool checkingForOverflow() { return EvalMode == EM_EvaluateForOverflow; }
bool checkingForUndefinedBehavior() { return CheckingForUndefinedBehavior; }
EvalInfo(const ASTContext &C, Expr::EvalStatus &S, EvaluationMode Mode)
: Ctx(const_cast<ASTContext &>(C)), EvalStatus(S), CurrentCall(nullptr),
@ -932,15 +921,12 @@ namespace {
switch (EvalMode) {
case EM_ConstantFold:
case EM_IgnoreSideEffects:
case EM_EvaluateForOverflow:
if (!HasFoldFailureDiagnostic)
break;
// We've already failed to fold something. Keep that diagnostic.
LLVM_FALLTHROUGH;
case EM_ConstantExpression:
case EM_PotentialConstantExpression:
case EM_ConstantExpressionUnevaluated:
case EM_PotentialConstantExpressionUnevaluated:
HasActiveDiagnostic = false;
return OptionalDiagnostic();
}
@ -986,8 +972,8 @@ namespace {
/// Diagnose that the evaluation does not produce a C++11 core constant
/// expression.
///
/// FIXME: Stop evaluating if we're in EM_ConstantExpression or
/// EM_PotentialConstantExpression mode and we produce one of these.
/// FIXME: Stop evaluating if we're in EM_ConstantExpression mode
/// and we produce one of these.
OptionalDiagnostic CCEDiag(SourceLocation Loc, diag::kind DiagId
= diag::note_invalid_subexpr_in_const_expr,
unsigned ExtraNotes = 0) {
@ -1023,16 +1009,16 @@ namespace {
/// couldn't model?
bool keepEvaluatingAfterSideEffect() {
switch (EvalMode) {
case EM_PotentialConstantExpression:
case EM_PotentialConstantExpressionUnevaluated:
case EM_EvaluateForOverflow:
case EM_IgnoreSideEffects:
return true;
case EM_ConstantExpression:
case EM_ConstantExpressionUnevaluated:
case EM_ConstantFold:
return false;
// By default, assume any side effect might be valid in some other
// evaluation of this expression from a different context.
return checkingPotentialConstantExpression() ||
checkingForUndefinedBehavior();
}
llvm_unreachable("Missed EvalMode case");
}
@ -1047,16 +1033,13 @@ namespace {
/// Should we continue evaluation after encountering undefined behavior?
bool keepEvaluatingAfterUndefinedBehavior() {
switch (EvalMode) {
case EM_EvaluateForOverflow:
case EM_IgnoreSideEffects:
case EM_ConstantFold:
return true;
case EM_PotentialConstantExpression:
case EM_PotentialConstantExpressionUnevaluated:
case EM_ConstantExpression:
case EM_ConstantExpressionUnevaluated:
return false;
return checkingForUndefinedBehavior();
}
llvm_unreachable("Missed EvalMode case");
}
@ -1076,16 +1059,12 @@ namespace {
return false;
switch (EvalMode) {
case EM_PotentialConstantExpression:
case EM_PotentialConstantExpressionUnevaluated:
case EM_EvaluateForOverflow:
return true;
case EM_ConstantExpression:
case EM_ConstantExpressionUnevaluated:
case EM_ConstantFold:
case EM_IgnoreSideEffects:
return false;
return checkingPotentialConstantExpression() ||
checkingForUndefinedBehavior();
}
llvm_unreachable("Missed EvalMode case");
}
@ -1142,9 +1121,7 @@ namespace {
Info.EvalStatus.Diag->empty() &&
!Info.EvalStatus.HasSideEffects),
OldMode(Info.EvalMode) {
if (Enabled &&
(Info.EvalMode == EvalInfo::EM_ConstantExpression ||
Info.EvalMode == EvalInfo::EM_ConstantExpressionUnevaluated))
if (Enabled)
Info.EvalMode = EvalInfo::EM_ConstantFold;
}
void keepDiagnostics() { Enabled = false; }
@ -1163,8 +1140,7 @@ namespace {
EvalInfo::EvaluationMode OldMode;
explicit IgnoreSideEffectsRAII(EvalInfo &Info)
: Info(Info), OldMode(Info.EvalMode) {
if (!Info.checkingPotentialConstantExpression())
Info.EvalMode = EvalInfo::EM_IgnoreSideEffects;
Info.EvalMode = EvalInfo::EM_IgnoreSideEffects;
}
~IgnoreSideEffectsRAII() { Info.EvalMode = OldMode; }
@ -2323,7 +2299,7 @@ static bool CheckedIntArithmetic(EvalInfo &Info, const Expr *E,
APSInt Value(Op(LHS.extend(BitWidth), RHS.extend(BitWidth)), false);
Result = Value.trunc(LHS.getBitWidth());
if (Result.extend(BitWidth) != Value) {
if (Info.checkingForOverflow())
if (Info.checkingForUndefinedBehavior())
Info.Ctx.getDiagnostics().Report(E->getExprLoc(),
diag::warn_integer_constant_overflow)
<< Result.toString(10) << E->getType();
@ -6047,6 +6023,8 @@ public:
// Always assume __builtin_constant_p(...) ? ... : ... is a potential
// constant expression; we can't check whether it's potentially foldable.
// FIXME: We should instead treat __builtin_constant_p as non-constant if
// it would return 'false' in this mode.
if (Info.checkingPotentialConstantExpression() && IsBcpCall)
return false;
@ -6329,7 +6307,7 @@ public:
bool VisitStmtExpr(const StmtExpr *E) {
// We will have checked the full-expressions inside the statement expression
// when they were completed, and don't need to check them again now.
if (Info.checkingForOverflow())
if (Info.checkingForUndefinedBehavior())
return Error(E);
BlockScopeRAII Scope(Info);
@ -9502,14 +9480,11 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
// size of the referenced object.
switch (Info.EvalMode) {
case EvalInfo::EM_ConstantExpression:
case EvalInfo::EM_PotentialConstantExpression:
case EvalInfo::EM_ConstantFold:
case EvalInfo::EM_EvaluateForOverflow:
case EvalInfo::EM_IgnoreSideEffects:
// Leave it to IR generation.
return Error(E);
case EvalInfo::EM_ConstantExpressionUnevaluated:
case EvalInfo::EM_PotentialConstantExpressionUnevaluated:
// Reduce it to a constant now.
return Success((Type & 2) ? 0 : -1, E);
}
@ -12549,8 +12524,9 @@ APSInt Expr::EvaluateKnownConstIntCheckOverflow(
EvalResult EVResult;
EVResult.Diag = Diag;
EvalInfo Info(Ctx, EVResult, EvalInfo::EM_EvaluateForOverflow);
EvalInfo Info(Ctx, EVResult, EvalInfo::EM_IgnoreSideEffects);
Info.InConstantContext = true;
Info.CheckingForUndefinedBehavior = true;
bool Result = ::EvaluateAsRValue(Info, this, EVResult.Val);
(void)Result;
@ -12567,7 +12543,8 @@ void Expr::EvaluateForOverflow(const ASTContext &Ctx) const {
bool IsConst;
EvalResult EVResult;
if (!FastEvaluateAsRValue(this, EVResult, Ctx, IsConst)) {
EvalInfo Info(Ctx, EVResult, EvalInfo::EM_EvaluateForOverflow);
EvalInfo Info(Ctx, EVResult, EvalInfo::EM_IgnoreSideEffects);
Info.CheckingForUndefinedBehavior = true;
(void)::EvaluateAsRValue(Info, this, EVResult.Val);
}
}
@ -13181,9 +13158,9 @@ bool Expr::isPotentialConstantExpr(const FunctionDecl *FD,
Expr::EvalStatus Status;
Status.Diag = &Diags;
EvalInfo Info(FD->getASTContext(), Status,
EvalInfo::EM_PotentialConstantExpression);
EvalInfo Info(FD->getASTContext(), Status, EvalInfo::EM_ConstantExpression);
Info.InConstantContext = true;
Info.CheckingPotentialConstantExpression = true;
const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(FD);
const CXXRecordDecl *RD = MD ? MD->getParent()->getCanonicalDecl() : nullptr;
@ -13222,8 +13199,9 @@ bool Expr::isPotentialConstantExprUnevaluated(Expr *E,
Status.Diag = &Diags;
EvalInfo Info(FD->getASTContext(), Status,
EvalInfo::EM_PotentialConstantExpressionUnevaluated);
EvalInfo::EM_ConstantExpressionUnevaluated);
Info.InConstantContext = true;
Info.CheckingPotentialConstantExpression = true;
// Fabricate a call stack frame to give the arguments a plausible cover story.
ArrayRef<const Expr*> Args;

3
clang/test/Sema/i-c-e.c
View File

@ -75,3 +75,6 @@ int realop[(__real__ 4) == 4 ? 1 : -1];
int imagop[(__imag__ 4) == 0 ? 1 : -1];
int *PR14729 = 0 ?: 1/0; // expected-error {{not a compile-time constant}} expected-warning 3{{}}
int bcp_call_v;
int bcp_call_a[] = {__builtin_constant_p(bcp_call_v && 0) ? bcp_call_v && 0 : -1};