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[c++20] P1152R4: warn on any simple-assignment to a volatile lvalue 

whose value is not ignored.

We don't warn on all the cases that are deprecated: specifically, we
choose to not warn for now if there are parentheses around the
assignment but its value is not actually used. This seems like a more
defensible rule, particularly for cases like sizeof(v = a), where the
parens are part of the operand rather than the sizeof syntax.

llvm-svn: 374135
This commit is contained in:
Richard Smith 2019-10-09 02:04:54 +00:00
parent 84ef9c6493
commit 4a6861a7e5
6 changed files with 124 additions and 29 deletions
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3
clang/include/clang/Basic/DiagnosticSemaKinds.td
View File

@ -6654,6 +6654,9 @@ def err_increment_decrement_enum : Error<
def warn_deprecated_increment_decrement_volatile : Warning<
"%select{decrement|increment}0 of object of volatile-qualified type %1 "
"is deprecated">, InGroup<DeprecatedVolatile>;
def warn_deprecated_simple_assign_volatile : Warning<
"use of result of assignment to object of volatile-qualified type %0 "
"is deprecated">, InGroup<DeprecatedVolatile>;
def warn_deprecated_compound_assign_volatile : Warning<
"compound assignment to object of volatile-qualified type %0 is deprecated">,
InGroup<DeprecatedVolatile>;

8
clang/include/clang/Sema/Sema.h
View File

@ -1062,6 +1062,11 @@ public:
llvm::SmallPtrSet<const Expr *, 8> PossibleDerefs;
/// Expressions appearing as the LHS of a volatile assignment in this
/// context. We produce a warning for these when popping the context if
/// they are not discarded-value expressions nor unevaluated operands.
SmallVector<Expr*, 2> VolatileAssignmentLHSs;
/// \brief Describes whether we are in an expression constext which we have
/// to handle differently.
enum ExpressionKind {
@ -4248,6 +4253,9 @@ public:
ExprResult TransformToPotentiallyEvaluated(Expr *E);
ExprResult HandleExprEvaluationContextForTypeof(Expr *E);
ExprResult CheckUnevaluatedOperand(Expr *E);
void CheckUnusedVolatileAssignment(Expr *E);
ExprResult ActOnConstantExpression(ExprResult Res);
// Functions for marking a declaration referenced. These functions also

51
clang/lib/Sema/SemaExpr.cpp
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@ -3801,6 +3801,16 @@ bool Sema::CheckUnaryExprOrTypeTraitOperand(Expr *E,
QualType ExprTy = E->getType();
assert(!ExprTy->isReferenceType());
bool IsUnevaluatedOperand =
(ExprKind == UETT_SizeOf || ExprKind == UETT_AlignOf ||
ExprKind == UETT_PreferredAlignOf);
if (IsUnevaluatedOperand) {
ExprResult Result = CheckUnevaluatedOperand(E);
if (Result.isInvalid())
return true;
E = Result.get();
}
if (ExprKind == UETT_VecStep)
return CheckVecStepTraitOperandType(*this, ExprTy, E->getExprLoc(),
E->getSourceRange());
@ -3838,9 +3848,8 @@ bool Sema::CheckUnaryExprOrTypeTraitOperand(Expr *E,
// The operand for sizeof and alignof is in an unevaluated expression context,
// so side effects could result in unintended consequences.
if ((ExprKind == UETT_SizeOf || ExprKind == UETT_AlignOf ||
ExprKind == UETT_PreferredAlignOf) &&
!inTemplateInstantiation() && E->HasSideEffects(Context, false))
if (IsUnevaluatedOperand && !inTemplateInstantiation() &&
E->HasSideEffects(Context, false))
Diag(E->getExprLoc(), diag::warn_side_effects_unevaluated_context);
if (CheckObjCTraitOperandConstraints(*this, ExprTy, E->getExprLoc(),
@ -3939,8 +3948,6 @@ bool Sema::CheckUnaryExprOrTypeTraitOperand(QualType ExprType,
}
static bool CheckAlignOfExpr(Sema &S, Expr *E, UnaryExprOrTypeTrait ExprKind) {
E = E->IgnoreParens();
// Cannot know anything else if the expression is dependent.
if (E->isTypeDependent())
return false;
@ -3952,9 +3959,10 @@ static bool CheckAlignOfExpr(Sema &S, Expr *E, UnaryExprOrTypeTrait ExprKind) {
}
ValueDecl *D = nullptr;
if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E)) {
Expr *Inner = E->IgnoreParens();
if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(Inner)) {
D = DRE->getDecl();
} else if (MemberExpr *ME = dyn_cast<MemberExpr>(E)) {
} else if (MemberExpr *ME = dyn_cast<MemberExpr>(Inner)) {
D = ME->getMemberDecl();
}
@ -11944,7 +11952,7 @@ QualType Sema::CheckAssignmentOperands(Expr *LHSExpr, ExprResult &RHS,
// A simple-assignment whose left operand is of a volatile-qualified
// type is deprecated unless the assignment is either a discarded-value
// expression or an unevaluated operand
// FIXME: Implement checks for this.
ExprEvalContexts.back().VolatileAssignmentLHSs.push_back(LHSExpr);
} else {
// C++2a [expr.ass]p6:
// [Compound-assignment] expressions are deprecated if E1 has
@ -15082,6 +15090,26 @@ void Sema::WarnOnPendingNoDerefs(ExpressionEvaluationContextRecord &Rec) {
Rec.PossibleDerefs.clear();
}
/// Check whether E, which is either a discarded-value expression or an
/// unevaluated operand, is a simple-assignment to a volatlie-qualified lvalue,
/// and if so, remove it from the list of volatile-qualified assignments that
/// we are going to warn are deprecated.
void Sema::CheckUnusedVolatileAssignment(Expr *E) {
if (!E->getType().isVolatileQualified() || !getLangOpts().CPlusPlus2a)
return;
// Note: ignoring parens here is not justified by the standard rules, but
// ignoring parentheses seems like a more reasonable approach, and this only
// drives a deprecation warning so doesn't affect conformance.
if (auto *BO = dyn_cast<BinaryOperator>(E->IgnoreParenImpCasts())) {
if (BO->getOpcode() == BO_Assign) {
auto &LHSs = ExprEvalContexts.back().VolatileAssignmentLHSs;
LHSs.erase(std::remove(LHSs.begin(), LHSs.end(), BO->getLHS()),
LHSs.end());
}
}
}
void Sema::PopExpressionEvaluationContext() {
ExpressionEvaluationContextRecord& Rec = ExprEvalContexts.back();
unsigned NumTypos = Rec.NumTypos;
@ -15116,6 +15144,13 @@ void Sema::PopExpressionEvaluationContext() {
WarnOnPendingNoDerefs(Rec);
// Warn on any volatile-qualified simple-assignments that are not discarded-
// value expressions nor unevaluated operands (those cases get removed from
// this list by CheckUnusedVolatileAssignment).
for (auto *BO : Rec.VolatileAssignmentLHSs)
Diag(BO->getBeginLoc(), diag::warn_deprecated_simple_assign_volatile)
<< BO->getType();
// When are coming out of an unevaluated context, clear out any
// temporaries that we may have created as part of the evaluation of
// the expression in that context: they aren't relevant because they

40
clang/lib/Sema/SemaExprCXX.cpp
View File

@ -499,6 +499,11 @@ ExprResult Sema::BuildCXXTypeId(QualType TypeInfoType,
}
}
ExprResult Result = CheckUnevaluatedOperand(E);
if (Result.isInvalid())
return ExprError();
E = Result.get();
// C++ [expr.typeid]p4:
// [...] If the type of the type-id is a reference to a possibly
// cv-qualified type, the result of the typeid expression refers to a
@ -6609,6 +6614,11 @@ ExprResult Sema::ActOnDecltypeExpression(Expr *E) {
ExprEvalContexts.back().ExprContext =
ExpressionEvaluationContextRecord::EK_Other;
Result = CheckUnevaluatedOperand(E);
if (Result.isInvalid())
return ExprError();
E = Result.get();
// In MS mode, don't perform any extra checking of call return types within a
// decltype expression.
if (getLangOpts().MSVCCompat)
@ -7233,7 +7243,10 @@ ExprResult Sema::BuildCXXNoexceptExpr(SourceLocation KeyLoc, Expr *Operand,
if (R.isInvalid())
return R;
// The operand may have been modified when checking the placeholder type.
R = CheckUnevaluatedOperand(R.get());
if (R.isInvalid())
return ExprError();
Operand = R.get();
if (!inTemplateInstantiation() && Operand->HasSideEffects(Context, false)) {
@ -7337,12 +7350,17 @@ ExprResult Sema::IgnoredValueConversions(Expr *E) {
// volatile lvalue with a special form, we perform an lvalue-to-rvalue
// conversion.
if (getLangOpts().CPlusPlus11 && E->isGLValue() &&
E->getType().isVolatileQualified() &&
IsSpecialDiscardedValue(E)) {
ExprResult Res = DefaultLvalueConversion(E);
if (Res.isInvalid())
return E;
E = Res.get();
E->getType().isVolatileQualified()) {
if (IsSpecialDiscardedValue(E)) {
ExprResult Res = DefaultLvalueConversion(E);
if (Res.isInvalid())
return E;
E = Res.get();
} else {
// Per C++2a [expr.ass]p5, a volatile assignment is not deprecated if
// it occurs as a discarded-value expression.
CheckUnusedVolatileAssignment(E);
}
}
// C++1z:
@ -7377,6 +7395,14 @@ ExprResult Sema::IgnoredValueConversions(Expr *E) {
return E;
}
ExprResult Sema::CheckUnevaluatedOperand(Expr *E) {
// Per C++2a [expr.ass]p5, a volatile assignment is not deprecated if
// it occurs as an unevaluated operand.
CheckUnusedVolatileAssignment(E);
return E;
}
// If we can unambiguously determine whether Var can never be used
// in a constant expression, return true.
// - if the variable and its initializer are non-dependent, then

49
clang/test/SemaCXX/deprecated.cpp
View File

@ -1,13 +1,17 @@
// RUN: %clang_cc1 -std=c++98 %s -Wdeprecated -verify -triple x86_64-linux-gnu
// RUN: %clang_cc1 -std=c++11 %s -Wdeprecated -verify -triple x86_64-linux-gnu
// RUN: %clang_cc1 -std=c++14 %s -Wdeprecated -verify -triple x86_64-linux-gnu
// RUN: %clang_cc1 -std=c++17 %s -Wdeprecated -verify -triple x86_64-linux-gnu
// RUN: %clang_cc1 -std=c++2a %s -Wdeprecated -verify=expected,cxx20 -triple x86_64-linux-gnu
// RUN: %clang_cc1 -std=c++98 %s -Wno-parentheses -Wdeprecated -verify -triple x86_64-linux-gnu
// RUN: %clang_cc1 -std=c++11 %s -Wno-parentheses -Wdeprecated -verify -triple x86_64-linux-gnu
// RUN: %clang_cc1 -std=c++14 %s -Wno-parentheses -Wdeprecated -verify -triple x86_64-linux-gnu
// RUN: %clang_cc1 -std=c++17 %s -Wno-parentheses -Wdeprecated -verify -triple x86_64-linux-gnu
// RUN: %clang_cc1 -std=c++2a %s -Wno-parentheses -Wdeprecated -verify=expected,cxx20 -triple x86_64-linux-gnu
// RUN: %clang_cc1 -std=c++14 %s -Wdeprecated -verify -triple x86_64-linux-gnu -Wno-deprecated-register -DNO_DEPRECATED_FLAGS
// RUN: %clang_cc1 -std=c++14 %s -Wno-parentheses -Wdeprecated -verify -triple x86_64-linux-gnu -Wno-deprecated-register -DNO_DEPRECATED_FLAGS
#include "Inputs/register.h"
namespace std {
struct type_info {};
}
void g() throw();
void h() throw(int);
void i() throw(...);
@ -133,17 +137,36 @@ namespace DeprecatedVolatile {
n = 5; // ok
#if __cplusplus >= 201103L
decltype(n = 5) m = n; // ok expected-warning {{side effects}}
m = sizeof(n = 5); // ok expected-warning {{side effects}}
(void)noexcept(n = 5); // ok expected-warning {{side effects}}
#endif
(void)typeid(n = 5); // ok expected-warning {{side effects}}
(n = 5, 0); // ok
use(n = 5); // FIXME: deprecated
(n = 5); // FIXME: deprecated
int q = n = 5; // FIXME: deprecated
q = n = 5; // FIXME: deprecated
use(n = 5); // cxx20-warning {{use of result of assignment to object of volatile-qualified type 'volatile int' is deprecated}}
int q = n = 5; // cxx20-warning {{deprecated}}
q = n = 5; // cxx20-warning {{deprecated}}
#if __cplusplus >= 201103L
decltype(q = n = 5) m2 = q; // FIXME: deprecated expected-warning {{side effects}}
decltype(q = n = 5) m2 = q; // cxx20-warning {{deprecated}} expected-warning {{side effects}}
(void)noexcept(q = n = 5); // cxx20-warning {{deprecated}} expected-warning {{side effects}}
#endif
q = sizeof(q = n = 5); // FIXME: deprecated expected-warning {{side effects}}
(void)sizeof(q = n = 5); // cxx20-warning {{deprecated}} expected-warning {{side effects}}
(void)typeid(use(n = 5)); // cxx20-warning {{deprecated}} expected-warning {{side effects}}
(void)__alignof(+(n = 5)); // cxx20-warning {{deprecated}} expected-warning {{side effects}}
// FIXME: These cases are technically deprecated because the parens are
// part of the operand, but we choose to not diagnose for now.
(void)sizeof(n = 5); // expected-warning {{side effects}}
(void)__alignof(n = 5); // expected-warning {{side effects}}
// Similarly here.
(n = 5);
volatile bool b = true;
if (b = true) {} // cxx20-warning {{deprecated}}
for (b = true;
b = true; // cxx20-warning {{deprecated}}
b = true) {}
for (volatile bool x = true;
volatile bool y = true; // ok despite volatile load from volatile initialization
) {}
// inc / dec / compound assignments are always deprecated
++n; // cxx20-warning {{increment of object of volatile-qualified type 'volatile int' is deprecated}}

2
clang/www/cxx_status.html
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@ -1103,7 +1103,7 @@ as the draft C++2a standard evolves.
<tr>
<td>Deprecate some problematic uses of <tt>volatile</tt></td>
<td><a href="http://wg21.link/p1152r4">P1152R4</a></td>
<td class="partial" align="center">Partial</td>
<td class="svn" align="center">SVN</td>
</tr>
<tr>
<td><tt>[[nodiscard("with reason")]]</tt></td>