sepavloff created this revision.
sepavloff added a reviewer: rsmith.
sepavloff requested review of this revision.
Herald added a project: clang.
The function HandleUnionActiveMemberChange determined union members that
become active by analyzing LHS expression. It works for assignment
operator but in the case of C++ assignment operator LHS is not easily
available. Actually RHS was used instead, wich resulted in crash
reported in PR45879.
This change uses LValue object to find union members.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D101429
Files:
clang/lib/AST/ExprConstant.cpp
clang/test/SemaCXX/constant-expression-cxx2a.cpp
Index: clang/test/SemaCXX/constant-expression-cxx2a.cpp
===================================================================
--- clang/test/SemaCXX/constant-expression-cxx2a.cpp
+++ clang/test/SemaCXX/constant-expression-cxx2a.cpp
@@ -379,10 +379,10 @@
return *p; // expected-note {{read of uninitialized object}}
}
static_assert(read_uninitialized() == 0); // expected-error {{constant}} expected-note {{in call}}
- constexpr void write_wrong_member_indirect() { // expected-error {{never produces a constant}}
+ constexpr void write_wrong_member_indirect() {
B b = {.b = 1};
int *p = &b.a.y;
- *p = 1; // expected-note {{assignment to member 'a' of union with active member 'b'}}
+ *p = 1;
}
constexpr int write_uninitialized() {
B b = {.b = 1};
@@ -1447,3 +1447,9 @@
constexpr bool b = [a = S(), b = S()] { return a.p == b.p; }();
static_assert(!b);
}
+
+namespace PR45879 {
+ struct Base { int m; };
+ struct Derived : Base {};
+ constexpr int k = ((Base{} = Derived{}), 0);
+}
Index: clang/lib/AST/ExprConstant.cpp
===================================================================
--- clang/lib/AST/ExprConstant.cpp
+++ clang/lib/AST/ExprConstant.cpp
@@ -5871,7 +5871,7 @@
/// operator whose left-hand side might involve a union member access. If it
/// does, implicitly start the lifetime of any accessed union elements per
/// C++20 [class.union]5.
-static bool HandleUnionActiveMemberChange(EvalInfo &Info, const Expr *LHSExpr,
+static bool HandleUnionActiveMemberChange(EvalInfo &Info, const Expr *E,
const LValue &LHS) {
if (LHS.InvalidBase || LHS.Designator.Invalid)
return false;
@@ -5879,11 +5879,11 @@
llvm::SmallVector<std::pair<unsigned, const FieldDecl*>, 4> UnionPathLengths;
// C++ [class.union]p5:
// define the set S(E) of subexpressions of E as follows:
- unsigned PathLength = LHS.Designator.Entries.size();
- for (const Expr *E = LHSExpr; E != nullptr;) {
+ for (unsigned PathLength = LHS.Designator.Entries.size(); PathLength;
+ --PathLength) {
+ SubobjectDesignator::PathEntry PE = LHS.Designator.Entries[PathLength - 1];
// -- If E is of the form A.B, S(E) contains the elements of S(A)...
- if (auto *ME = dyn_cast<MemberExpr>(E)) {
- auto *FD = dyn_cast<FieldDecl>(ME->getMemberDecl());
+ if (auto *FD = PE.getAsFieldOrNull()) {
// Note that we can't implicitly start the lifetime of a reference,
// so we don't need to proceed any further if we reach one.
if (!FD || FD->getType()->isReferenceType())
@@ -5900,41 +5900,10 @@
UnionPathLengths.push_back({PathLength - 1, FD});
}
- E = ME->getBase();
- --PathLength;
- assert(declaresSameEntity(
- FD, LHS.Designator.Entries[PathLength].getAsBaseOrMember()));
-
// -- If E is of the form A[B] and is interpreted as a built-in array
// subscripting operator, S(E) is [S(the array operand, if any)].
- } else if (auto *ASE = dyn_cast<ArraySubscriptExpr>(E)) {
- // Step over an ArrayToPointerDecay implicit cast.
- auto *Base = ASE->getBase()->IgnoreImplicit();
- if (!Base->getType()->isArrayType())
- break;
-
- E = Base;
- --PathLength;
-
- } else if (auto *ICE = dyn_cast<ImplicitCastExpr>(E)) {
- // Step over a derived-to-base conversion.
- E = ICE->getSubExpr();
- if (ICE->getCastKind() == CK_NoOp)
- continue;
- if (ICE->getCastKind() != CK_DerivedToBase &&
- ICE->getCastKind() != CK_UncheckedDerivedToBase)
- break;
- // Walk path backwards as we walk up from the base to the derived class.
- for (const CXXBaseSpecifier *Elt : llvm::reverse(ICE->path())) {
- --PathLength;
- (void)Elt;
- assert(
- declaresSameEntity(Elt->getType()->getAsCXXRecordDecl(),
- LHS.Designator.Entries[PathLength].getAsBase()));
- }
-
- // -- Otherwise, S(E) is empty.
- } else {
+ // -- Otherwise, S(E) is empty.
+ } else if (!PE.isArrayIndex() && !PE.isAnyBase()) {
break;
}
}
@@ -5946,7 +5915,7 @@
// if modification of X [would access an inactive union member], an object
// of the type of X is implicitly created
CompleteObject Obj =
- findCompleteObject(Info, LHSExpr, AK_Assign, LHS, LHSExpr->getType());
+ findCompleteObject(Info, E, AK_Assign, LHS, E->getType());
if (!Obj)
return false;
for (std::pair<unsigned, const FieldDecl *> LengthAndField :
@@ -5958,8 +5927,8 @@
bool DuringInit = Info.isEvaluatingCtorDtor(LHS.Base, D.Entries) ==
ConstructionPhase::AfterBases;
StartLifetimeOfUnionMemberHandler StartLifetime{
- Info, LHSExpr, LengthAndField.second, DuringInit};
- if (!findSubobject(Info, LHSExpr, Obj, D, StartLifetime))
+ Info, E, LengthAndField.second, DuringInit};
+ if (!findSubobject(Info, E, Obj, D, StartLifetime))
return false;
}
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