Reject a slightly-sneaky way to perform a read of mutable state from within a
constexpr function. Part of this fix is a tentative fix for an as-yet-unfiled
core issue (we're missing a prohibition against reading mutable members from
unions via a trivial constructor/assignment, since that doesn't perform an
lvalue-to-rvalue conversion on the members).
llvm-svn: 217852
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 155d9be..743e59f 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -2080,6 +2080,64 @@
Array.swap(NewValue);
}
+/// Determine whether a type would actually be read by an lvalue-to-rvalue
+/// conversion. If it's of class type, we may assume that the copy operation
+/// is trivial. Note that this is never true for a union type with fields
+/// (because the copy always "reads" the active member) and always true for
+/// a non-class type.
+static bool isReadByLvalueToRvalueConversion(QualType T) {
+ CXXRecordDecl *RD = T->getBaseElementTypeUnsafe()->getAsCXXRecordDecl();
+ if (!RD || (RD->isUnion() && !RD->field_empty()))
+ return true;
+ if (RD->isEmpty())
+ return false;
+
+ for (auto *Field : RD->fields())
+ if (isReadByLvalueToRvalueConversion(Field->getType()))
+ return true;
+
+ for (auto &BaseSpec : RD->bases())
+ if (isReadByLvalueToRvalueConversion(BaseSpec.getType()))
+ return true;
+
+ return false;
+}
+
+/// Diagnose an attempt to read from any unreadable field within the specified
+/// type, which might be a class type.
+static bool diagnoseUnreadableFields(EvalInfo &Info, const Expr *E,
+ QualType T) {
+ CXXRecordDecl *RD = T->getBaseElementTypeUnsafe()->getAsCXXRecordDecl();
+ if (!RD)
+ return false;
+
+ if (!RD->hasMutableFields())
+ return false;
+
+ for (auto *Field : RD->fields()) {
+ // If we're actually going to read this field in some way, then it can't
+ // be mutable. If we're in a union, then assigning to a mutable field
+ // (even an empty one) can change the active member, so that's not OK.
+ // FIXME: Add core issue number for the union case.
+ if (Field->isMutable() &&
+ (RD->isUnion() || isReadByLvalueToRvalueConversion(Field->getType()))) {
+ Info.Diag(E, diag::note_constexpr_ltor_mutable, 1) << Field;
+ Info.Note(Field->getLocation(), diag::note_declared_at);
+ return true;
+ }
+
+ if (diagnoseUnreadableFields(Info, E, Field->getType()))
+ return true;
+ }
+
+ for (auto &BaseSpec : RD->bases())
+ if (diagnoseUnreadableFields(Info, E, BaseSpec.getType()))
+ return true;
+
+ // All mutable fields were empty, and thus not actually read.
+ return false;
+}
+
/// Kinds of access we can perform on an object, for diagnostics.
enum AccessKinds {
AK_Read,
@@ -2135,6 +2193,14 @@
}
if (I == N) {
+ // If we are reading an object of class type, there may still be more
+ // things we need to check: if there are any mutable subobjects, we
+ // cannot perform this read. (This only happens when performing a trivial
+ // copy or assignment.)
+ if (ObjType->isRecordType() && handler.AccessKind == AK_Read &&
+ diagnoseUnreadableFields(Info, E, ObjType))
+ return handler.failed();
+
if (!handler.found(*O, ObjType))
return false;