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 Do we have a mechanism to avoid folding get_nsdmi's trees that I've missed? > > Either I can tweak p_c_e to say that a FIX_TRUNC_EXPR in a template > > is not potentially constant, or I can just remove the whole F_T_E > > case, since: > > a) we could not have created an IMPLICIT_CONV_EXPR here, and > > b) similar code, FLOAT_EXPR, is not handled here, either. > > > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/11? > > > > PR c++/102990 > > > > gcc/cp/ChangeLog: > > > > * pt.cc (tsubst_copy_and_build) <case FIX_TRUNC_EXPR>: Remove. > > > > gcc/testsuite/ChangeLog: > > > > * g++.dg/cpp0x/nsdmi-template22.C: New test. > > * g++.dg/cpp0x/nsdmi-template23.C: New test. > > --- > > gcc/cp/pt.cc | 4 ---- > > gcc/testsuite/g++.dg/cpp0x/nsdmi-template22.C | 13 +++++++++++++ > > gcc/testsuite/g++.dg/cpp0x/nsdmi-template23.C | 13 +++++++++++++ > > 3 files changed, 26 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/pt.cc b/gcc/cp/pt.cc > > index 715eea27577..a3becc19290 100644 > > --- a/gcc/cp/pt.cc > > +++ b/gcc/cp/pt.cc > > @@ -20184,10 +20184,6 @@ tsubst_copy_and_build (tree t, > > templated_operator_saved_lookups (t), > > complain|decltype_flag)); > > - case FIX_TRUNC_EXPR: > > - /* convert_like should have created an IMPLICIT_CONV_EXPR. */ > > - gcc_unreachable (); > > - > > case ADDR_EXPR: > > op1 = TREE_OPERAND (t, 0); > > if (TREE_CODE (op1) == LABEL_DECL) > > 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: 5d2233f4033dfa37ad88dc2eab138524fe64242e > Marek