rZhBoYao created this revision.
rZhBoYao added reviewers: aaron.ballman, Endill, clang-language-wg.
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rZhBoYao requested review of this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.
Add -Windeterminately-sequenced and fix -Wunsequenced according to P0400R0 and
CWG2571.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D156057
Files:
clang/docs/ReleaseNotes.rst
clang/include/clang/Basic/DiagnosticGroups.td
clang/include/clang/Basic/DiagnosticSemaKinds.td
clang/lib/Sema/SemaChecking.cpp
clang/test/SemaCXX/warn-unsequenced.cpp
Index: clang/test/SemaCXX/warn-unsequenced.cpp
===================================================================
--- clang/test/SemaCXX/warn-unsequenced.cpp
+++ clang/test/SemaCXX/warn-unsequenced.cpp
@@ -1,7 +1,7 @@
// RUN: %clang_cc1 -fsyntax-only -verify=cxx11 -std=c++11 -Wno-unused -Wno-uninitialized \
// RUN: -Wunsequenced -Wno-c++17-extensions -Wno-c++14-extensions %s
-// RUN: %clang_cc1 -fsyntax-only -verify=cxx17 -std=c++17 -Wno-unused -Wno-uninitialized \
-// RUN: -Wunsequenced -Wno-c++17-extensions -Wno-c++14-extensions %s
+// RUN: %clang_cc1 -fsyntax-only -verify=cxx17 -std=c++23 -Wno-unused -Wno-uninitialized \
+// RUN: -Wunsequenced %s
int f(int, int = 0);
int g1();
@@ -40,15 +40,15 @@
a = (a++, a++); // cxx11-warning {{multiple unsequenced modifications to 'a'}}
f(a, a); // ok
f(a = 0, a); // cxx11-warning {{unsequenced modification and access to 'a'}}
- // cxx17-warning@-1 {{unsequenced modification and access to 'a'}}
+ // cxx17-warning@-1 {{indeterminately sequenced modification and access to 'a'}}
f(a, a += 0); // cxx11-warning {{unsequenced modification and access to 'a'}}
- // cxx17-warning@-1 {{unsequenced modification and access to 'a'}}
+ // cxx17-warning@-1 {{indeterminately sequenced modification and access to 'a'}}
f(a = 0, a = 0); // cxx11-warning {{multiple unsequenced modifications to 'a'}}
- // cxx17-warning@-1 {{multiple unsequenced modifications to 'a'}}
+ // cxx17-warning@-1 {{multiple indeterminately sequenced modifications to 'a'}}
a = f(++a); // ok
a = f(a++); // ok
a = f(++a, a++); // cxx11-warning {{multiple unsequenced modifications to 'a'}}
- // cxx17-warning@-1 {{multiple unsequenced modifications to 'a'}}
+ // cxx17-warning@-1 {{multiple indeterminately sequenced modifications to 'a'}}
// Compound assignment "A OP= B" is equivalent to "A = A OP B" except that A
// is evaluated only once.
@@ -279,15 +279,18 @@
// cxx11-warning@-1 {{multiple unsequenced modifications to 'i'}}
(i++, f)(i++, 42); // cxx11-warning {{multiple unsequenced modifications to 'i'}}
+ f((++i, f)(i++, j++), ++j); // cxx11-warning {{multiple unsequenced modifications to 'i'}}
+ // cxx11-warning@-1 {{multiple unsequenced modifications to 'j'}}
+ // cxx17-warning@-2 {{multiple indeterminately sequenced modifications to 'j'}}
(i++ + i++, f)(42, 42); // cxx11-warning {{multiple unsequenced modifications to 'i'}}
// cxx17-warning@-1 {{multiple unsequenced modifications to 'i'}}
int (*pf)(int, int);
(pf = f)(pf != nullptr, pf != nullptr); // cxx11-warning {{unsequenced modification and access to 'pf'}}
pf((pf = f) != nullptr, 42); // cxx11-warning {{unsequenced modification and access to 'pf'}}
f((pf = f, 42), (pf = f, 42)); // cxx11-warning {{multiple unsequenced modifications to 'pf'}}
- // cxx17-warning@-1 {{multiple unsequenced modifications to 'pf'}}
+ // cxx17-warning@-1 {{multiple indeterminately sequenced modifications to 'pf'}}
pf((pf = f) != nullptr, pf == nullptr); // cxx11-warning {{unsequenced modification and access to 'pf'}}
- // cxx17-warning@-1 {{unsequenced modification and access to 'pf'}}
+ // cxx17-warning@-1 {{indeterminately sequenced modification and access to 'pf'}}
}
namespace PR20819 {
@@ -305,7 +308,11 @@
E &operator=(E &);
E operator()(E);
E operator()(E, E);
+#if __cplusplus >= 202302L
+ E operator[](auto...);
+#else
E operator[](E);
+#endif
} e;
// Binary operators with unsequenced operands.
E operator+(E,E);
@@ -417,7 +424,7 @@
operator+=(((void)i++,e), ((void)i++,e));
// cxx11-warning@-1 {{multiple unsequenced modifications to 'i'}}
- // cxx17-warning@-2 {{multiple unsequenced modifications to 'i'}}
+ // cxx17-warning@-2 {{multiple indeterminately sequenced modifications to 'i'}}
// Binary operators where the LHS is sequenced before the RHS in C++17.
((void)i++,e) << ((void)i++,e);
@@ -435,16 +442,21 @@
operator<<(((void)i++,e), ((void)i++,e));
// cxx11-warning@-1 {{multiple unsequenced modifications to 'i'}}
- // cxx17-warning@-2 {{multiple unsequenced modifications to 'i'}}
+ // cxx17-warning@-2 {{multiple indeterminately sequenced modifications to 'i'}}
+#if __cplusplus >= 202302L
+ ((void)i++,e)[((void)i++,e), ++i];
+ // cxx17-warning@-1 {{multiple indeterminately sequenced modifications to 'i'}}
+#else
((void)i++,e)[((void)i++,e)];
// cxx11-warning@-1 {{multiple unsequenced modifications to 'i'}}
+#endif
((void)i++,e)(((void)i++,e));
// cxx11-warning@-1 {{multiple unsequenced modifications to 'i'}}
e(((void)i++,e), ((void)i++,e));
// cxx11-warning@-1 {{multiple unsequenced modifications to 'i'}}
- // cxx17-warning@-2 {{multiple unsequenced modifications to 'i'}}
+ // cxx17-warning@-2 {{multiple indeterminately sequenced modifications to 'i'}}
((void)i++,e).operator()(((void)i++,e));
// cxx11-warning@-1 {{multiple unsequenced modifications to 'i'}}
@@ -464,7 +476,7 @@
operator<<(operator<<(s, i++), i++);
// cxx11-warning@-1 {{multiple unsequenced modifications to 'i'}}
- // cxx17-warning@-2 {{multiple unsequenced modifications to 'i'}}
+ // cxx17-warning@-2 {{multiple indeterminately sequenced modifications to 'i'}}
}
}
@@ -805,7 +817,7 @@
foo(num++, num++);
// cxx11-warning@-1 {{multiple unsequenced modifications to 'num'}}
- // cxx17-warning@-2 {{multiple unsequenced modifications to 'num'}}
+ // cxx17-warning@-2 {{multiple indeterminately sequenced modifications to 'num'}}
return 1;
}
Index: clang/lib/Sema/SemaChecking.cpp
===================================================================
--- clang/lib/Sema/SemaChecking.cpp
+++ clang/lib/Sema/SemaChecking.cpp
@@ -15692,6 +15692,8 @@
};
SmallVector<Value, 8> Values;
+ const SequenceChecker &SC;
+
public:
/// A region within an expression which may be sequenced with respect
/// to some other region.
@@ -15706,7 +15708,9 @@
Seq() : Index(0) {}
};
- SequenceTree() { Values.push_back(Value(0)); }
+ SequenceTree(const SequenceChecker &SC) : SC(SC) {
+ Values.push_back(Value(0));
+ }
Seq root() const { return Seq(0); }
/// Create a new sequence of operations, which is an unsequenced
@@ -15736,6 +15740,29 @@
return false;
}
+ /// Determine whether two operations are indeterminately sequenced. This
+ /// operation is asymmetric: \p Cur should be the more recent sequence, and
+ /// \p Old should have been merged into its parent as appropriate.
+ bool isIndeterminatelySequenced(Seq Cur, Seq Old) {
+ unsigned C = representative(Cur.Index);
+ unsigned Target = representative(Old.Index);
+ for (Seq seq : llvm::iterator_range(SC.CallPostfixExprs.rbegin(),
+ SC.CallPostfixExprs.rend())) {
+ unsigned Sibling = seq.Index;
+ unsigned Parent = Values[Sibling].Parent;
+ if (Target <= Sibling)
+ continue;
+ if ((Target = Values[Target].Parent) != Parent)
+ continue;
+ while (C >= Target) {
+ if (C == Target)
+ return true;
+ C = Values[C].Parent;
+ }
+ }
+ return false;
+ }
+
private:
/// Pick a representative for a sequence.
unsigned representative(unsigned K) {
@@ -15788,7 +15815,7 @@
Sema &SemaRef;
/// Sequenced regions within the expression.
- SequenceTree Tree;
+ SequenceTree Tree = *this;
/// Declaration modifications and references which we have seen.
UsageInfoMap UsageMap;
@@ -15800,10 +15827,6 @@
/// (that is, post-increment operations).
SmallVectorImpl<std::pair<Object, Usage>> *ModAsSideEffect = nullptr;
- /// Expressions to check later. We defer checking these to reduce
- /// stack usage.
- SmallVectorImpl<const Expr *> &WorkList;
-
/// RAII object wrapping the visitation of a sequenced subexpression of an
/// expression. At the end of this process, the side-effects of the evaluation
/// become sequenced with respect to the value computation of the result, so
@@ -15864,6 +15887,22 @@
bool EvalOK = true;
} *EvalTracker = nullptr;
+ /// RAII object tracking the visitation of CallExpr and that of its
+ /// subexpressions.
+ struct InCallExprArgs {
+ InCallExprArgs(SequenceChecker &SC) : SC(SC) {
+ SC.CallPostfixExprs.push_back(SC.Region);
+ };
+
+ ~InCallExprArgs() { SC.CallPostfixExprs.pop_back(); }
+
+ private:
+ SequenceChecker &SC;
+ };
+
+ /// Only modified by InCallExprArgs
+ SmallVector<SequenceTree::Seq, 4> CallPostfixExprs;
+
/// Find the object which is produced by the specified expression,
/// if any.
Object getObject(const Expr *E, bool Mod) const {
@@ -15892,7 +15931,11 @@
void addUsage(Object O, UsageInfo &UI, const Expr *UsageExpr, UsageKind UK) {
// Get the old usage for the given object and usage kind.
Usage &U = UI.Uses[UK];
- if (!U.UsageExpr || !Tree.isUnsequenced(Region, U.Seq)) {
+ bool FoundUnsequenced = U.UsageExpr && Tree.isUnsequenced(Region, U.Seq);
+ bool FoundIndeterminatelySequenced =
+ U.UsageExpr && SemaRef.LangOpts.CPlusPlus17 &&
+ Tree.isIndeterminatelySequenced(Region, U.Seq);
+ if (!FoundUnsequenced && !FoundIndeterminatelySequenced) {
// If we have a modification as side effect and are in a sequenced
// subexpression, save the old Usage so that we can restore it later
// in SequencedSubexpression::~SequencedSubexpression.
@@ -15915,7 +15958,11 @@
return;
const Usage &U = UI.Uses[OtherKind];
- if (!U.UsageExpr || !Tree.isUnsequenced(Region, U.Seq))
+ bool FoundUnsequenced = U.UsageExpr && Tree.isUnsequenced(Region, U.Seq);
+ bool FoundIndeterminatelySequenced =
+ U.UsageExpr && SemaRef.LangOpts.CPlusPlus17 &&
+ Tree.isIndeterminatelySequenced(Region, U.Seq);
+ if (!FoundUnsequenced && !FoundIndeterminatelySequenced)
return;
const Expr *Mod = U.UsageExpr;
@@ -15925,8 +15972,12 @@
SemaRef.DiagRuntimeBehavior(
Mod->getExprLoc(), {Mod, ModOrUse},
- SemaRef.PDiag(IsModMod ? diag::warn_unsequenced_mod_mod
- : diag::warn_unsequenced_mod_use)
+ SemaRef.PDiag(!FoundUnsequenced && FoundIndeterminatelySequenced
+ ? IsModMod
+ ? diag::warn_indeterminately_sequenced_mod_mod
+ : diag::warn_indeterminately_sequenced_mod_use
+ : IsModMod ? diag::warn_unsequenced_mod_mod
+ : diag::warn_unsequenced_mod_use)
<< O << SourceRange(ModOrUse->getExprLoc()));
UI.Diagnosed = true;
}
@@ -15985,13 +16036,9 @@
}
public:
- SequenceChecker(Sema &S, const Expr *E,
- SmallVectorImpl<const Expr *> &WorkList)
- : Base(S.Context), SemaRef(S), Region(Tree.root()), WorkList(WorkList) {
+ SequenceChecker(Sema &S, const Expr *E)
+ : Base(S.Context), SemaRef(S), Region(Tree.root()) {
Visit(E);
- // Silence a -Wunused-private-field since WorkList is now unused.
- // TODO: Evaluate if it can be used, and if not remove it.
- (void)this->WorkList;
}
void VisitStmt(const Stmt *S) {
@@ -16332,43 +16379,48 @@
// the value computation of its result].
SequencedSubexpression Sequenced(*this);
SemaRef.runWithSufficientStackSpace(CE->getExprLoc(), [&] {
+ if (!SemaRef.getLangOpts().CPlusPlus17)
+ return Base::VisitCallExpr(CE);
+
// C++17 [expr.call]p5
// The postfix-expression is sequenced before each expression in the
// expression-list and any default argument. [...]
- SequenceTree::Seq CalleeRegion;
- SequenceTree::Seq OtherRegion;
- if (SemaRef.getLangOpts().CPlusPlus17) {
- CalleeRegion = Tree.allocate(Region);
- OtherRegion = Tree.allocate(Region);
- } else {
- CalleeRegion = Region;
- OtherRegion = Region;
- }
- SequenceTree::Seq OldRegion = Region;
-
- // Visit the callee expression first.
+ SequenceTree::Seq Parent = Region;
+ SequenceTree::Seq CalleeRegion = Tree.allocate(Parent);
Region = CalleeRegion;
- if (SemaRef.getLangOpts().CPlusPlus17) {
+ {
SequencedSubexpression Sequenced(*this);
- Visit(CE->getCallee());
- } else {
- Visit(CE->getCallee());
+ Visit(isa<CXXOperatorCallExpr>(CE) ? CE->getArg(0) : CE->getCallee());
}
- // Then visit the argument expressions.
- Region = OtherRegion;
- for (const Expr *Argument : CE->arguments())
+ // C++17 [expr.call]p5
+ // [...] The initialization of a parameter, including every associated
+ // value computation and side effect, is indeterminately sequenced with
+ // respect to that of any other parameter.
+ SmallVector<SequenceTree::Seq, 16> Args;
+ auto ArgRange =
+ isa<CXXOperatorCallExpr>(CE)
+ ? llvm::iterator_range(CE->arg_begin() + 1, CE->arg_end())
+ : CE->arguments();
+ InCallExprArgs _(*this);
+ for (const Expr *Argument : ArgRange) {
+ SequencedSubexpression Sequenced(*this);
+ Region = Tree.allocate(Parent);
+ Args.push_back(Region);
Visit(Argument);
-
- Region = OldRegion;
- if (SemaRef.getLangOpts().CPlusPlus17) {
- Tree.merge(CalleeRegion);
- Tree.merge(OtherRegion);
}
+
+ Region = Parent;
+ Tree.merge(CalleeRegion);
+ for (SequenceTree::Seq region : Args)
+ Tree.merge(region);
});
}
void VisitCXXOperatorCallExpr(const CXXOperatorCallExpr *CXXOCE) {
+ if (!SemaRef.getLangOpts().CPlusPlus17)
+ return VisitCallExpr(CXXOCE);
+
// C++17 [over.match.oper]p2:
// [...] the operator notation is first transformed to the equivalent
// function-call notation as summarized in Table 12 (where @ denotes one
@@ -16379,15 +16431,11 @@
// From the above only overloaded binary operators and overloaded call
// operators have sequencing rules in C++17 that we need to handle
// separately.
- if (!SemaRef.getLangOpts().CPlusPlus17 ||
- (CXXOCE->getNumArgs() != 2 && CXXOCE->getOperator() != OO_Call))
- return VisitCallExpr(CXXOCE);
-
enum {
NoSequencing,
LHSBeforeRHS,
RHSBeforeLHS,
- LHSBeforeRest
+ IndeterminatelySequenced
} SequencingKind;
switch (CXXOCE->getOperator()) {
case OO_Equal:
@@ -16403,28 +16451,49 @@
case OO_GreaterGreaterEqual:
SequencingKind = RHSBeforeLHS;
break;
-
case OO_LessLess:
case OO_GreaterGreater:
case OO_AmpAmp:
case OO_PipePipe:
case OO_Comma:
case OO_ArrowStar:
- case OO_Subscript:
SequencingKind = LHSBeforeRHS;
break;
-
+ case OO_Subscript:
+ SequencingKind = SemaRef.getLangOpts().CPlusPlus23
+ ? IndeterminatelySequenced // CWG2571
+ : LHSBeforeRHS;
+ break;
case OO_Call:
- SequencingKind = LHSBeforeRest;
+ SequencingKind = IndeterminatelySequenced;
break;
-
default:
SequencingKind = NoSequencing;
break;
}
- if (SequencingKind == NoSequencing)
- return VisitCallExpr(CXXOCE);
+ if (SequencingKind == NoSequencing) {
+ SequenceTree::Seq Parent = Region;
+ SequenceTree::Seq CalleeRegion = Tree.allocate(Parent);
+ SequenceTree::Seq OtherRegion = Tree.allocate(Parent);
+
+ // Visit the callee expression first.
+ Region = CalleeRegion;
+ {
+ SequencedSubexpression Sequenced(*this);
+ Visit(CXXOCE->getCallee());
+ }
+
+ // Then visit the argument expressions.
+ Region = OtherRegion;
+ for (const Expr *Argument : CXXOCE->arguments())
+ Visit(Argument);
+
+ Region = Parent;
+ Tree.merge(CalleeRegion);
+ Tree.merge(OtherRegion);
+ return;
+ }
// This is a call, so all subexpressions are sequenced before the result.
SequencedSubexpression Sequenced(*this);
@@ -16432,63 +16501,31 @@
SemaRef.runWithSufficientStackSpace(CXXOCE->getExprLoc(), [&] {
assert(SemaRef.getLangOpts().CPlusPlus17 &&
"Should only get there with C++17 and above!");
- assert((CXXOCE->getNumArgs() == 2 || CXXOCE->getOperator() == OO_Call) &&
- "Should only get there with an overloaded binary operator"
- " or an overloaded call operator!");
-
- if (SequencingKind == LHSBeforeRest) {
- assert(CXXOCE->getOperator() == OO_Call &&
- "We should only have an overloaded call operator here!");
-
- // This is very similar to VisitCallExpr, except that we only have the
- // C++17 case. The postfix-expression is the first argument of the
- // CXXOperatorCallExpr. The expressions in the expression-list, if any,
- // are in the following arguments.
- //
- // Note that we intentionally do not visit the callee expression since
- // it is just a decayed reference to a function.
- SequenceTree::Seq PostfixExprRegion = Tree.allocate(Region);
- SequenceTree::Seq ArgsRegion = Tree.allocate(Region);
- SequenceTree::Seq OldRegion = Region;
+ if (SequencingKind == IndeterminatelySequenced) {
+ assert((CXXOCE->getOperator() == OO_Subscript ||
+ CXXOCE->getOperator() == OO_Call) &&
+ "We should only have an overloaded call or subscript operator "
+ "here!");
assert(CXXOCE->getNumArgs() >= 1 &&
- "An overloaded call operator must have at least one argument"
- " for the postfix-expression!");
- const Expr *PostfixExpr = CXXOCE->getArgs()[0];
- llvm::ArrayRef<const Expr *> Args(CXXOCE->getArgs() + 1,
- CXXOCE->getNumArgs() - 1);
-
- // Visit the postfix-expression first.
- {
- Region = PostfixExprRegion;
- SequencedSubexpression Sequenced(*this);
- Visit(PostfixExpr);
- }
-
- // Then visit the argument expressions.
- Region = ArgsRegion;
- for (const Expr *Arg : Args)
- Visit(Arg);
-
- Region = OldRegion;
- Tree.merge(PostfixExprRegion);
- Tree.merge(ArgsRegion);
- } else {
- assert(CXXOCE->getNumArgs() == 2 &&
- "Should only have two arguments here!");
- assert((SequencingKind == LHSBeforeRHS ||
- SequencingKind == RHSBeforeLHS) &&
- "Unexpected sequencing kind!");
-
- // We do not visit the callee expression since it is just a decayed
- // reference to a function.
- const Expr *E1 = CXXOCE->getArg(0);
- const Expr *E2 = CXXOCE->getArg(1);
- if (SequencingKind == RHSBeforeLHS)
- std::swap(E1, E2);
-
- return VisitSequencedExpressions(E1, E2);
+ "An overloaded call or subscript operator must have at least "
+ "one argument for the postfix-expression!");
+ return VisitCallExpr(CXXOCE);
}
+ assert(CXXOCE->getNumArgs() == 2 &&
+ "Should only have two arguments here!");
+ assert(
+ (SequencingKind == LHSBeforeRHS || SequencingKind == RHSBeforeLHS) &&
+ "Unexpected sequencing kind!");
+
+ // We do not visit the callee expression since it is just a decayed
+ // reference to a function.
+ const Expr *E1 = CXXOCE->getArg(0);
+ const Expr *E2 = CXXOCE->getArg(1);
+ if (SequencingKind == RHSBeforeLHS)
+ std::swap(E1, E2);
+
+ return VisitSequencedExpressions(E1, E2);
});
}
@@ -16542,12 +16579,7 @@
} // namespace
void Sema::CheckUnsequencedOperations(const Expr *E) {
- SmallVector<const Expr *, 8> WorkList;
- WorkList.push_back(E);
- while (!WorkList.empty()) {
- const Expr *Item = WorkList.pop_back_val();
- SequenceChecker(*this, Item, WorkList);
- }
+ SequenceChecker(*this, E);
}
void Sema::CheckCompletedExpr(Expr *E, SourceLocation CheckLoc,
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2291,6 +2291,12 @@
"multiple unsequenced modifications to %0">, InGroup<Unsequenced>;
def warn_unsequenced_mod_use : Warning<
"unsequenced modification and access to %0">, InGroup<Unsequenced>;
+def warn_indeterminately_sequenced_mod_mod : Warning<
+ "multiple indeterminately sequenced modifications to %0">,
+ InGroup<IndeterminatelySequenced>;
+def warn_indeterminately_sequenced_mod_use : Warning<
+ "indeterminately sequenced modification and access to %0">,
+ InGroup<IndeterminatelySequenced>;
def select_initialized_entity_kind : TextSubstitution<
"%select{copying variable|copying parameter|initializing template parameter|"
Index: clang/include/clang/Basic/DiagnosticGroups.td
===================================================================
--- clang/include/clang/Basic/DiagnosticGroups.td
+++ clang/include/clang/Basic/DiagnosticGroups.td
@@ -688,6 +688,7 @@
def XorUsedAsPow : DiagGroup<"xor-used-as-pow">;
def Unsequenced : DiagGroup<"unsequenced">;
+def IndeterminatelySequenced : DiagGroup<"indeterminately-sequenced">;
// GCC name for -Wunsequenced
def : DiagGroup<"sequence-point", [Unsequenced]>;
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -453,6 +453,42 @@
- Clang now emits ``-Wconstant-logical-operand`` warning even when constant logical
operand is on left side.
(`#37919 <https://github.com/llvm/llvm-project/issues/37919>`_)
+- Added a new warning group ``-Windeterminately-sequenced`` to diagnose indeterminately
+ sequenced accesses amongst the initializations of each function parameter, as is the
+ case from C++17 onwards. Accordingly, ``-Wunsequenced`` no longer falsely diagnoses
+ such accesses as unsequenced.
+ (`#63935 <https://github.com/llvm/llvm-project/issues/63935>`_)
+
+ *Example C++23 Code*:
+
+ .. code-block:: c++
+
+ struct S { int operator[](auto...); };
+ int c{}, d{}, f(int, int = {}),
+ a = f(c++, (++d, f)(!c, !d)),
+ b = S()[f(f(c++)), c++];
+
+ *BEFORE*:
+
+ .. code-block:: text
+
+ <source>:3:12: warning: unsequenced modification and access to 'c' [-Wunsequenced]
+ 3 | a = f(c++, (++d, f)(!c, !d)),
+ | ^ ~
+ <source>:4:18: warning: multiple unsequenced modifications to 'c' [-Wunsequenced]
+ 4 | b = S()[f(f(c++)), c++];
+ | ^ ~~
+
+ *AFTER*:
+
+ .. code-block:: text
+
+ <source>:3:12: warning: indeterminately sequenced modification and access to 'c' [-Windeterminately-sequenced]
+ 3 | a = f(c++, (++d, f)(!c, !d)),
+ | ^ ~
+ <source>:4:18: warning: multiple indeterminately sequenced modifications to 'c' [-Windeterminately-sequenced]
+ 4 | b = S()[f(f(c++)), c++];
+ | ^ ~~
Bug Fixes in This Version
-------------------------
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