On 22/05/2019 01:15, Richard Smith via cfe-commits wrote:
Author: rsmith
Date: Tue May 21 16:15:20 2019
New Revision: 361329
URL: http://llvm.org/viewvc/llvm-project?rev=361329&view=rev
Log:
[c++20] P1330R0: permit simple-assignments that change the active member
of a union within constant expression evaluation.
[...]
--- cfe/trunk/lib/AST/ExprConstant.cpp (original)
+++ cfe/trunk/lib/AST/ExprConstant.cpp Tue May 21 16:15:20 2019
[...]> @@ -4888,6 +4916,159 @@ static bool HandleDynamicCast(EvalInfo &
[...]
+/// Handle a builtin simple-assignment or a call to a trivial assignment
+/// 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,
+ const LValue &LHS) {
+ if (LHS.InvalidBase || LHS.Designator.Invalid)
+ return false;
+
+ llvm::SmallVector<std::pair<unsigned, const FieldDecl*>, 4> UnionPathLengths;
+ // C++ [class.union]p5:
+ // define the set S(E) of subexpressions of E as follows:
+ const Expr *E = LHSExpr;
+ unsigned PathLength = LHS.Designator.Entries.size();
+ while (E) {
+ // -- 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 (!FD)
+ break;
+
+ // ... and also contains A.B if B names a union member
+ if (FD->getParent()->isUnion())
+ UnionPathLengths.push_back({PathLength - 1, FD});
+
+ E = ME->getBase();
+ --PathLength;
+ assert(declaresSameEntity(FD,
+ LHS.Designator.Entries[PathLength]
+ .getAsBaseOrMember().getPointer()));
+
+ // -- 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.
+ if (ICE->getCastKind() == CK_NoOp)
+ continue;
+ if (ICE->getCastKind() != CK_DerivedToBase &&
+ ICE->getCastKind() != CK_UncheckedDerivedToBase)
+ break;
+ for (const CXXBaseSpecifier *Elt : ICE->path()) {
+ --PathLength;
+ assert(declaresSameEntity(Elt->getType()->getAsCXXRecordDecl(),
+ LHS.Designator.Entries[PathLength]
+ .getAsBaseOrMember().getPointer()));
the above assert fires for the below test.cc with `clang++ -std=c++2a
-fsyntax-only test.cc`:
struct S1 { int n; };
struct S2: S1 {};
struct S3: S2 {};
void f() {
S3 s;
s.n = 0;
}
_______________________________________________
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
