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Fix hang during constant evaluation of union assignment. 

HandleUnionActiveMemberChange forgot to walk over a nop implicit
conversion node and got stuck in the process.

As a cleanup I changed the declaration of `E` so it can't
be accidentally accessed after the loop.

llvm-svn: 361571
This commit is contained in:
Eric Fiselier 2019-05-23 23:34:43 +00:00
parent 093c922205
commit ffafdb9afc
2 changed files with 10 additions and 3 deletions
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5
clang/lib/AST/ExprConstant.cpp
View File

@ -4994,9 +4994,8 @@ static bool HandleUnionActiveMemberChange(EvalInfo &Info, const Expr *LHSExpr,
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) {
for (const Expr *E = LHSExpr; E != nullptr;) {
// -- 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());
@ -5026,6 +5025,7 @@ static bool HandleUnionActiveMemberChange(EvalInfo &Info, const Expr *LHSExpr,
} 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 &&
@ -5038,7 +5038,6 @@ static bool HandleUnionActiveMemberChange(EvalInfo &Info, const Expr *LHSExpr,
LHS.Designator.Entries[PathLength]
.getAsBaseOrMember().getPointer()));
}
E = ICE->getSubExpr();
// -- Otherwise, S(E) is empty.
} else {

8
clang/test/SemaCXX/constant-expression-cxx2a.cpp
View File

@ -513,4 +513,12 @@ namespace Union {
static_assert(return_init_all().a.p == 7); // expected-error {{}} expected-note {{read of member 'p' of union with no active member}}
static_assert(return_init_all().a.q == 8); // expected-error {{}} expected-note {{read of member 'q' of union with no active member}}
constexpr B init_all = return_init_all();
constexpr bool test_no_member_change = []{
union U { char dummy = {}; };
U u1;
U u2;
u1 = u2;
return true;
}();
}