| Message ID | 20170228224834.GU1849@tucnak |
|---|---|
| State | New |
| Headers | show |
On Tue, Feb 28, 2017 at 12:48 PM, Jakub Jelinek <jakub@redhat.com> wrote: > The DR1659/DR1611 changes result in construct_virtual_base not being called, > but unfortunately the call generated in there was the spot that caused > mark_exp_read on the arguments passed to the vbase construction (TREE_USED > is set on these earlier already during parsing them). That results > in false positive -Wunused-but-set-parameter warnings. > > The following patch tries to avoid the warning in that case by marking > the arguments as read (essentially pretending they were read in the omitted > call). Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? I believe there's some question still about whether the DR1659/11 changes are what we want; I'll defer to Nathan on this patch. Jason > 2017-02-28 Jakub Jelinek <jakub@redhat.com> > > PR c++/79746 > * init.c (emit_mem_initializers): When not constructing vbases of > abstract classes, mark arguments as read for > -Wunused-but-set-parameter. > > * g++.dg/warn/Wunused-parm-9.C: New test. > > --- gcc/cp/init.c.jj 2017-02-28 16:24:05.000000000 +0100 > +++ gcc/cp/init.c 2017-02-28 21:08:29.158380881 +0100 > @@ -1217,6 +1217,12 @@ emit_mem_initializers (tree mem_inits) > /* C++14 DR1658 Means we do not have to construct vbases of > abstract classes. */ > construct_virtual_base (subobject, arguments); > + else > + /* When not constructing vbases of abstract classes, at least mark > + the arguments expressions as read to avoid > + -Wunused-but-set-parameter false positives. */ > + for (tree arg = arguments; arg; arg = TREE_CHAIN (arg)) > + mark_exp_read (TREE_VALUE (arg)); > > if (inherited_base) > pop_deferring_access_checks (); > --- gcc/testsuite/g++.dg/warn/Wunused-parm-9.C.jj 2017-02-28 21:11:44.989820368 +0100 > +++ gcc/testsuite/g++.dg/warn/Wunused-parm-9.C 2017-02-28 21:10:43.000000000 +0100 > @@ -0,0 +1,12 @@ > +// PR c++/79746 > +// { dg-do compile } > +// { dg-options "-Wunused-but-set-parameter" } > + > +struct A { > + A (const char *x) : a(x) {} // { dg-bogus "set but not used" } > + virtual int foo () = 0; > + const char *a; > +}; > +struct B : public virtual A { > + B (const char *x) : A(x) {} // { dg-bogus "set but not used" } > +}; > > Jakub
On 02/28/2017 02:41 PM, Jason Merrill wrote: > On Tue, Feb 28, 2017 at 12:48 PM, Jakub Jelinek <jakub@redhat.com> wrote: >> The DR1659/DR1611 changes result in construct_virtual_base not being called, >> but unfortunately the call generated in there was the spot that caused >> mark_exp_read on the arguments passed to the vbase construction (TREE_USED >> is set on these earlier already during parsing them). That results >> in false positive -Wunused-but-set-parameter warnings. >> >> The following patch tries to avoid the warning in that case by marking >> the arguments as read (essentially pretending they were read in the omitted >> call). Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? > > I believe there's some question still about whether the DR1659/11 > changes are what we want; I'll defer to Nathan on this patch. Jakub's patch is OK. The defect I've reported is how 1658 interacts with virtual destructors. (bug 79393) nathan
--- gcc/cp/init.c.jj 2017-02-28 16:24:05.000000000 +0100 +++ gcc/cp/init.c 2017-02-28 21:08:29.158380881 +0100 @@ -1217,6 +1217,12 @@ emit_mem_initializers (tree mem_inits) /* C++14 DR1658 Means we do not have to construct vbases of abstract classes. */ construct_virtual_base (subobject, arguments); + else + /* When not constructing vbases of abstract classes, at least mark + the arguments expressions as read to avoid + -Wunused-but-set-parameter false positives. */ + for (tree arg = arguments; arg; arg = TREE_CHAIN (arg)) + mark_exp_read (TREE_VALUE (arg)); if (inherited_base) pop_deferring_access_checks (); --- gcc/testsuite/g++.dg/warn/Wunused-parm-9.C.jj 2017-02-28 21:11:44.989820368 +0100 +++ gcc/testsuite/g++.dg/warn/Wunused-parm-9.C 2017-02-28 21:10:43.000000000 +0100 @@ -0,0 +1,12 @@ +// PR c++/79746 +// { dg-do compile } +// { dg-options "-Wunused-but-set-parameter" } + +struct A { + A (const char *x) : a(x) {} // { dg-bogus "set but not used" } + virtual int foo () = 0; + const char *a; +}; +struct B : public virtual A { + B (const char *x) : A(x) {} // { dg-bogus "set but not used" } +};