| Message ID | c4cfe14b-34c2-67f6-4954-85cc5e347ba5@acm.org |
|---|---|
| State | New |
| Headers | show |
On Fri, Jan 20, 2017 at 8:15 AM, Nathan Sidwell <nathan@acm.org> wrote: > Bug 78495 is a wrong code bug caused by an invisiref parm. When building > the inherited ctor, we use forward_parm to create a forwarding reference. > That code generation considers the type of the parm to be 'T'. We thus end > up with a tree that looks like *&PARM > > The subsequent call gets 'CALL_FROM_THUNK' set. We need that set so code > generation doesn't copy pass-by-invisiref objects that are specified by the > C abi (but not specified so by the C++ abi) (POD structs, commonly). > > cp_genericize is used to mutate invisiref parm_decls from T to &T and bash > their uses from PARM to *PARM (with suitable checking of &PARM turning into > plain PARM). However it explicitly skips genericizing the args of a > CALL_FROM_THUNK tree. Thus we end up taking the address of the reference > parm itself. > > That appears to be incorrect now we have forward_parm. This patch deletes > that skipping. Hmm, I would guess that if we're going to do this we need to also use forward_parm in maybe_thunk_body. Jason
On 01/20/2017 08:45 AM, Jason Merrill wrote: > Hmm, I would guess that if we're going to do this we need to also use > forward_parm in maybe_thunk_body. Apparently not needed. maybe_thunk_body is called after we've genericized the parent ctor. That ctor's parms have been bashed to reference and have DECL_BY_REFERENCE set appropriately. The clone's parms have also been bashed, but do not have DECL_BY_REFERENCE set. For POD struct (which remain as struct T) the backend machinery already DTRT. nathan
On Fri, Jan 20, 2017 at 11:12 AM, Nathan Sidwell <nathan@acm.org> wrote: > On 01/20/2017 08:45 AM, Jason Merrill wrote: > >> Hmm, I would guess that if we're going to do this we need to also use >> forward_parm in maybe_thunk_body. > > > Apparently not needed. maybe_thunk_body is called after we've genericized > the parent ctor. That ctor's parms have been bashed to reference and have > DECL_BY_REFERENCE set appropriately. The clone's parms have also been > bashed, but do not have DECL_BY_REFERENCE set. > > For POD struct (which remain as struct T) the backend machinery already > DTRT. OK, then. Jason
2017-01-20 Nathan Sidwell <nathan@acm.org> PR c++/78495 - wrong code inherited ctor and invisi-ref parm * cp-gimplify.c (cp_generize_r): Don't skip thunks. PR c++/79495 * g++.dg/cpp1z/inh-ctor38.C: New. Index: cp/cp-gimplify.c =================================================================== --- cp/cp-gimplify.c (revision 244596) +++ cp/cp-gimplify.c (working copy) @@ -1103,15 +1103,7 @@ cp_genericize_r (tree *stmt_p, int *walk && omp_var_to_track (stmt)) omp_cxx_notice_variable (wtd->omp_ctx, stmt); - /* Don't dereference parms in a thunk, pass the references through. */ - if ((TREE_CODE (stmt) == CALL_EXPR && CALL_FROM_THUNK_P (stmt)) - || (TREE_CODE (stmt) == AGGR_INIT_EXPR && AGGR_INIT_FROM_THUNK_P (stmt))) - { - *walk_subtrees = 0; - return NULL; - } - - /* Otherwise, do dereference invisible reference parms. */ + /* Dereference invisible reference parms. */ if (wtd->handle_invisiref_parm_p && is_invisiref_parm (stmt)) { *stmt_p = convert_from_reference (stmt); Index: testsuite/g++.dg/cpp1z/inh-ctor38.C =================================================================== --- testsuite/g++.dg/cpp1z/inh-ctor38.C (revision 0) +++ testsuite/g++.dg/cpp1z/inh-ctor38.C (working copy) @@ -0,0 +1,31 @@ +// { dg-do run { target c++11 } } +// PR78495 failed to propagate pass-by-value struct to base ctor. + +struct Ptr { + void *ptr = 0; + + Ptr() {} + Ptr(Ptr const&) = delete; + Ptr(Ptr&& other) : ptr (other.ptr) {} +}; + +struct Base { + Ptr val; + Base(Ptr val_) : val(static_cast<Ptr&&>(val_)) {} +}; + +struct Derived: Base { + using Base::Base; +}; + +void *Foo () { + Ptr ptr; + + Derived d(static_cast<Ptr&&>(ptr)); + + return d.val.ptr; +} + +int main () { + return Foo () != 0; +}