Refactor CompareReferenceRelationship and its callers in preparation for
implementing the resolution of CWG2352.
No functionality change, except that we now convert the referent of a
reference binding to the underlying type of the reference in more cases;
we used to happen to preserve the type sugar from the referent if the
only type change was in the cv-qualifiers.
This exposed a bug in how we generate code for trivial assignment
operators: if the type sugar (particularly the may_alias attribute)
got lost during reference binding, we'd use the "wrong" TBAA information
for the load during the assignment.
diff --git a/clang/lib/CodeGen/CGExprCXX.cpp b/clang/lib/CodeGen/CGExprCXX.cpp
index 269b80b..3fc8613 100644
--- a/clang/lib/CodeGen/CGExprCXX.cpp
+++ b/clang/lib/CodeGen/CGExprCXX.cpp
@@ -241,16 +241,28 @@
}
}
+ bool TrivialForCodegen =
+ MD->isTrivial() || (MD->isDefaulted() && MD->getParent()->isUnion());
+ bool TrivialAssignment =
+ TrivialForCodegen &&
+ (MD->isCopyAssignmentOperator() || MD->isMoveAssignmentOperator()) &&
+ !MD->getParent()->mayInsertExtraPadding();
+
// C++17 demands that we evaluate the RHS of a (possibly-compound) assignment
// operator before the LHS.
CallArgList RtlArgStorage;
CallArgList *RtlArgs = nullptr;
+ LValue TrivialAssignmentRHS;
if (auto *OCE = dyn_cast<CXXOperatorCallExpr>(CE)) {
if (OCE->isAssignmentOp()) {
- RtlArgs = &RtlArgStorage;
- EmitCallArgs(*RtlArgs, MD->getType()->castAs<FunctionProtoType>(),
- drop_begin(CE->arguments(), 1), CE->getDirectCallee(),
- /*ParamsToSkip*/0, EvaluationOrder::ForceRightToLeft);
+ if (TrivialAssignment) {
+ TrivialAssignmentRHS = EmitLValue(CE->getArg(1));
+ } else {
+ RtlArgs = &RtlArgStorage;
+ EmitCallArgs(*RtlArgs, MD->getType()->castAs<FunctionProtoType>(),
+ drop_begin(CE->arguments(), 1), CE->getDirectCallee(),
+ /*ParamsToSkip*/0, EvaluationOrder::ForceRightToLeft);
+ }
}
}
@@ -281,22 +293,25 @@
return RValue::get(nullptr);
}
- if (MD->isTrivial() || (MD->isDefaulted() && MD->getParent()->isUnion())) {
- if (isa<CXXDestructorDecl>(MD)) return RValue::get(nullptr);
- if (!MD->getParent()->mayInsertExtraPadding()) {
- if (MD->isCopyAssignmentOperator() || MD->isMoveAssignmentOperator()) {
- // We don't like to generate the trivial copy/move assignment operator
- // when it isn't necessary; just produce the proper effect here.
- LValue RHS = isa<CXXOperatorCallExpr>(CE)
- ? MakeNaturalAlignAddrLValue(
- (*RtlArgs)[0].getRValue(*this).getScalarVal(),
- (*(CE->arg_begin() + 1))->getType())
- : EmitLValue(*CE->arg_begin());
- EmitAggregateAssign(This, RHS, CE->getType());
- return RValue::get(This.getPointer(*this));
- }
- llvm_unreachable("unknown trivial member function");
+ if (TrivialForCodegen) {
+ if (isa<CXXDestructorDecl>(MD))
+ return RValue::get(nullptr);
+
+ if (TrivialAssignment) {
+ // We don't like to generate the trivial copy/move assignment operator
+ // when it isn't necessary; just produce the proper effect here.
+ // It's important that we use the result of EmitLValue here rather than
+ // emitting call arguments, in order to preserve TBAA information from
+ // the RHS.
+ LValue RHS = isa<CXXOperatorCallExpr>(CE)
+ ? TrivialAssignmentRHS
+ : EmitLValue(*CE->arg_begin());
+ EmitAggregateAssign(This, RHS, CE->getType());
+ return RValue::get(This.getPointer(*this));
}
+
+ assert(MD->getParent()->mayInsertExtraPadding() &&
+ "unknown trivial member function");
}
// Compute the function type we're calling.