================
@@ -95,9 +106,59 @@ bool ExprSequence::inSequence(const Stmt *Before, const
Stmt *After) const {
return true;
}
+ SmallVector<const Stmt *, 1> BeforeParents = getParentStmts(Before, Context);
+
+ // Since C++17, the callee of a call expression is guaranteed to be sequenced
+ // before all of the arguments.
+ // We handle this as a special case rather than using the general
+ // `getSequenceSuccessor` logic above because the callee expression doesn't
+ // have an unambiguous successor; the order in which arguments are evaluated
+ // is indeterminate.
+ for (const Stmt *Parent : BeforeParents) {
+ // Special case: If the callee is a `MemberExpr` with a `DeclRefExpr` as
its
+ // base, we consider it to be sequenced _after_ the arguments. This is
+ // because the variable referenced in the base will only actually be
+ // accessed when the call happens, i.e. once all of the arguments have been
+ // evaluated. This has no basis in the C++ standard, but it reflects actual
+ // behavior that is relevant to a use-after-move scenario:
+ //
+ // ```
+ // a.bar(consumeA(std::move(a));
+ // ```
+ //
+ // In this example, we end up accessing `a` after it has been moved from,
+ // even though nominally the callee `a.bar` is evaluated before the
argument
+ // `consumeA(std::move(a))`. Note that this is not specific to C++17, so
+ // we implement this logic unconditionally.
+ if (const auto *call = dyn_cast<CXXMemberCallExpr>(Parent)) {
+ if (argsContain(call, Before) &&
+ isa<DeclRefExpr>(
+ call->getImplicitObjectArgument()->IgnoreParenImpCasts()) &&
+ isDescendantOrEqual(After, call->getImplicitObjectArgument(),
+ Context))
+ return true;
+
+ // We need this additional early exit so that we don't fall through to
the
+ // more general logic below.
+ if (auto *Member = dyn_cast<MemberExpr>(Before);
----------------
EugeneZelenko wrote:
```suggestion
if (const auto *Member = dyn_cast<MemberExpr>(Before);
```
https://github.com/llvm/llvm-project/pull/93623
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