| Message ID | YjykYDP3avLDvlhP@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] c++: FIX_TRUNC_EXPR in tsubst [PR102990] | expand |
On 3/24/22 13:03, Marek Polacek wrote: > On Thu, Mar 24, 2022 at 09:32:19AM -0400, Jason Merrill wrote: >> On 3/23/22 19:26, Marek Polacek wrote: >>> On Wed, Mar 23, 2022 at 04:35:32PM -0400, Jason Merrill wrote: >>>> On 3/22/22 19:55, Marek Polacek wrote: >>>>> This is a crash where a FIX_TRUNC_EXPR gets into tsubst_copy_and_build >>>>> where it hits gcc_unreachable (). >>>>> >>>>> The history of tsubst_copy_and_build/FIX_TRUNC_EXPR is such that it >>>>> was introduced in r181478, but it did the wrong thing, whereupon it >>>>> was turned into gcc_unreachable () in r258821 (see this thread: >>>>> <https://gcc.gnu.org/pipermail/gcc-patches/2018-March/495853.html>). >>>>> >>>>> In a template, we should never create a FIX_TRUNC_EXPR (that's what >>>>> conv_unsafe_in_template_p is for). But in this test we are NOT in >>>>> a template when we call digest_nsdmi_init which ends up calling >>>>> convert_like, converting 1.0e+0 to int, so convert_to_integer_1 >>>>> gives us a FIX_TRUNC_EXPR. >>>>> >>>>> But then when we get to parsing f's parameters, we are in a template >>>>> when processing decltype(Helpers{}), and since r268321, when the >>>>> compound literal isn't instantiation-dependent and the type isn't >>>>> type-dependent, finish_compound_literal falls back to the normal >>>>> processing, so it calls digest_init, which does fold_non_dependent_init >>>>> and since the FIX_TRUNC_EXPR isn't dependent, we instantiate and >>>>> therefore crash in tsubst_copy_and_build. >>>> >>>> Hmm, we shouldn't be doing fold_non_dependent_init on the result of >>>> get_nsdmi. Why does that happen? >>> >>> OK, so we have decltype(Helpers{}), finish_compound_literal gets >>> Helpers{}, it's not type-dependent, so: >>> >>> - call digest_init (type=Helpers, init={}) >>> init is BRACE_ENCLOSED_INITIALIZER_P, type is !TYPE_NON_AGGREGATE_CLASS >>> so go down to... >>> - process_init_constructor_record (type=Helpers, init={}) >>> - we walk the fields of Helpers, there's 'inputs' of type knob_t >>> type_build_ctor_call (knob_t) is true, we want to default-init this >>> field >>> - create a {} as the init for default-initialization >>> - call massage_init_elt (type=knob_t, init={}) to adjust the init >>> - we do so by calling digest_init_r (type=knob_t, init={}) >>> - here we again call process_init_constructor_record, walk knob_t's >>> fields, see the field 'value', it has a DECL_INITIAL, so call >>> get_nsdmi, that returns the FIX_TRUNC_EXPR we've created before >>> - so digesting {} for knob_t produced >>> init = {.value=(int) NON_LVALUE_EXPR <1.0e+0>} >>> - then we call fold_non_dependent_init on this init, and die >> >> Maybe we shouldn't call fold_non_dependent_init on a CONSTRUCTOR here, since >> presumably we already called it on elements that needed it in the recursive >> digest_init_r. > > Ah, that works. It's still a bit weird that we don't treat FLOAT_EXPR and > FIX_TRUNC_EXPR the same. > > I've tried to remove the call to fold_non_dependent_init in massage_init_elt > to see what breaks...a lot. So it has to stay at least in this form. > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? OK. > Thanks, > > -- >8 -- > This is a crash where a FIX_TRUNC_EXPR gets into tsubst_copy_and_build > where it hits gcc_unreachable (). > > The history of tsubst_copy_and_build/FIX_TRUNC_EXPR is such that it > was introduced in r181478, but it did the wrong thing, whereupon it > was turned into gcc_unreachable () in r258821 (see this thread: > <https://gcc.gnu.org/pipermail/gcc-patches/2018-March/495853.html>). > > In a template, we should never create a FIX_TRUNC_EXPR (that's what > conv_unsafe_in_template_p is for). But in this test we are NOT in > a template when we call digest_nsdmi_init which ends up calling > convert_like, converting 1.0e+0 to int, so convert_to_integer_1 > gives us a FIX_TRUNC_EXPR. > > But then when we get to parsing f's parameters, we are in a template > when processing decltype(Helpers{}), and since r268321, when the > compound literal isn't instantiation-dependent and the type isn't > type-dependent, finish_compound_literal falls back to the normal > processing, so it calls digest_init, which does fold_non_dependent_init > and since the FIX_TRUNC_EXPR isn't dependent, we instantiate and > therefore crash in tsubst_copy_and_build. > > The fateful call to fold_non_dependent_init comes from massage_init_elt, > We shouldn't be calling f_n_d_i on the result of get_nsdmi. This we can > avoid by eschewing calling f_n_d_i on CONSTRUCTORs; their elements have > already been folded. > > PR c++/102990 > > gcc/cp/ChangeLog: > > * typeck2.cc (massage_init_elt): Avoid folding CONSTRUCTORs. > > gcc/testsuite/ChangeLog: > > * g++.dg/cpp0x/nsdmi-template22.C: New test. > * g++.dg/cpp0x/nsdmi-template23.C: New test. > --- > gcc/cp/typeck2.cc | 13 +++++++++---- > gcc/testsuite/g++.dg/cpp0x/nsdmi-template22.C | 13 +++++++++++++ > gcc/testsuite/g++.dg/cpp0x/nsdmi-template23.C | 13 +++++++++++++ > 3 files changed, 35 insertions(+), 4 deletions(-) > create mode 100644 gcc/testsuite/g++.dg/cpp0x/nsdmi-template22.C > create mode 100644 gcc/testsuite/g++.dg/cpp0x/nsdmi-template23.C > > diff --git a/gcc/cp/typeck2.cc b/gcc/cp/typeck2.cc > index a4c825fc34d..cebe6acf487 100644 > --- a/gcc/cp/typeck2.cc > +++ b/gcc/cp/typeck2.cc > @@ -1433,10 +1433,15 @@ massage_init_elt (tree type, tree init, int nested, int flags, > new_flags |= LOOKUP_AGGREGATE_PAREN_INIT; > init = digest_init_r (type, init, nested ? 2 : 1, new_flags, complain); > /* When we defer constant folding within a statement, we may want to > - defer this folding as well. */ > - tree t = fold_non_dependent_init (init, complain); > - if (TREE_CONSTANT (t)) > - init = t; > + defer this folding as well. Don't call this on CONSTRUCTORs because > + their elements have already been folded, and we must avoid folding > + the result of get_nsdmi. */ > + if (TREE_CODE (init) != CONSTRUCTOR) > + { > + tree t = fold_non_dependent_init (init, complain); > + if (TREE_CONSTANT (t)) > + init = t; > + } > return init; > } > > diff --git a/gcc/testsuite/g++.dg/cpp0x/nsdmi-template22.C b/gcc/testsuite/g++.dg/cpp0x/nsdmi-template22.C > new file mode 100644 > index 00000000000..4ed2501035c > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp0x/nsdmi-template22.C > @@ -0,0 +1,13 @@ > +// PR c++/102990 > +// { dg-do compile { target c++11 } } > + > +struct knob_t { > + /* Let's create a FIX_TRUNC_EXPR. */ > + int value = 1.0; > +}; > + > +struct Helpers { > + knob_t inputs; > +}; > + > +template<class> void f(decltype(Helpers{})); > diff --git a/gcc/testsuite/g++.dg/cpp0x/nsdmi-template23.C b/gcc/testsuite/g++.dg/cpp0x/nsdmi-template23.C > new file mode 100644 > index 00000000000..240cab4347a > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp0x/nsdmi-template23.C > @@ -0,0 +1,13 @@ > +// PR c++/102990 > +// { dg-do compile { target c++11 } } > + > +struct knob_t { > + /* Let's create a FLOAT_EXPR. */ > + double value = 1UL; > +}; > + > +struct Helpers { > + knob_t inputs; > +}; > + > +template<class> void f(decltype(Helpers{})); > > base-commit: fb488cba571539b6644e8f99f1dd997cdb4c82c1
diff --git a/gcc/cp/typeck2.cc b/gcc/cp/typeck2.cc index a4c825fc34d..cebe6acf487 100644 --- a/gcc/cp/typeck2.cc +++ b/gcc/cp/typeck2.cc @@ -1433,10 +1433,15 @@ massage_init_elt (tree type, tree init, int nested, int flags, new_flags |= LOOKUP_AGGREGATE_PAREN_INIT; init = digest_init_r (type, init, nested ? 2 : 1, new_flags, complain); /* When we defer constant folding within a statement, we may want to - defer this folding as well. */ - tree t = fold_non_dependent_init (init, complain); - if (TREE_CONSTANT (t)) - init = t; + defer this folding as well. Don't call this on CONSTRUCTORs because + their elements have already been folded, and we must avoid folding + the result of get_nsdmi. */ + if (TREE_CODE (init) != CONSTRUCTOR) + { + tree t = fold_non_dependent_init (init, complain); + if (TREE_CONSTANT (t)) + init = t; + } return init; } diff --git a/gcc/testsuite/g++.dg/cpp0x/nsdmi-template22.C b/gcc/testsuite/g++.dg/cpp0x/nsdmi-template22.C new file mode 100644 index 00000000000..4ed2501035c --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/nsdmi-template22.C @@ -0,0 +1,13 @@ +// PR c++/102990 +// { dg-do compile { target c++11 } } + +struct knob_t { + /* Let's create a FIX_TRUNC_EXPR. */ + int value = 1.0; +}; + +struct Helpers { + knob_t inputs; +}; + +template<class> void f(decltype(Helpers{})); diff --git a/gcc/testsuite/g++.dg/cpp0x/nsdmi-template23.C b/gcc/testsuite/g++.dg/cpp0x/nsdmi-template23.C new file mode 100644 index 00000000000..240cab4347a --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/nsdmi-template23.C @@ -0,0 +1,13 @@ +// PR c++/102990 +// { dg-do compile { target c++11 } } + +struct knob_t { + /* Let's create a FLOAT_EXPR. */ + double value = 1UL; +}; + +struct Helpers { + knob_t inputs; +}; + +template<class> void f(decltype(Helpers{}));