| Message ID | 20210831012638.3293672-1-ppalka@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | c++: check arity before deduction w/ explicit targs [PR12672] | expand |
On 8/30/21 9:26 PM, Patrick Palka wrote: > During overload resolution, when the arity of a function template > clearly disagrees with the arity of the call, no specialization of the > function template could yield a viable candidate. The deduction routine > type_unification_real already notices this situation, but not before > it substitutes explicit template arguments into the template, a step > which could induce a hard error. Although it's necessary to perform > this substitution first in order to check arity perfectly (since the > substitution can e.g. expand a non-trailing parameter pack), in most > cases we can determine ahead of time whether there's an arity > disagreement without needing to perform deduction. > > To that end, this patch implements an (approximate) arity check in > add_template_candidate_real that guards actual deduction. It's enabled > only when there are explicit template arguments since that's when > deduction can force otherwise avoidable template instantiations. (I > experimented with enabling it unconditionally as an optimization and > saw some compile-time improvements of about 5% but also some regressions > by about the same magnitude, so kept it conditional.) > > In passing, this adds a least_p parameter to arity_rejection for sake > of consistent diagnostics with unify_arity. > > A couple of testcases needed to be adjusted so that deduction continues > to occur as intended after this change. Except in unify6.C, where we > were expecting foo<void ()> to be ill-formed due to substitution > yielding a function type with an added 'const', but I think this is > permitted by [dcl.fct]/7, so I changed the test accordingly. Agreed. > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for > trunk? OK, thanks. > PR c++/12672 > > gcc/cp/ChangeLog: > > * call.c (rejection_reason::call_varargs_p): Rename this > previously unused member to ... > (rejection_reason::least_p): ... this. > (arity_rejection): Add least_p parameter. > (add_template_candidate_real): When there are explicit > template arguments, check that the arity of the call agrees with > the arity of the function before attempting deduction. > (print_arity_information): Add least_p parameter. > (print_z_candidate): Adjust call to print_arity_information. > > gcc/testsuite/ChangeLog: > > * g++.dg/cpp0x/decltype29.C: Adjust. > * g++.dg/template/error56.C: Adjust. > * g++.old-deja/g++.pt/unify6.C: Adjust. > * g++.dg/template/explicit-args6.C: New test. > --- > gcc/cp/call.c | 67 ++++++++++++++++--- > gcc/testsuite/g++.dg/cpp0x/decltype29.C | 4 +- > gcc/testsuite/g++.dg/template/error56.C | 4 +- > .../g++.dg/template/explicit-args6.C | 33 +++++++++ > gcc/testsuite/g++.old-deja/g++.pt/unify6.C | 4 +- > 5 files changed, 96 insertions(+), 16 deletions(-) > create mode 100644 gcc/testsuite/g++.dg/template/explicit-args6.C > > diff --git a/gcc/cp/call.c b/gcc/cp/call.c > index e4df72ec1a3..80e6121ce44 100644 > --- a/gcc/cp/call.c > +++ b/gcc/cp/call.c > @@ -455,8 +455,8 @@ struct rejection_reason { > int expected; > /* The actual number of arguments in the call. */ > int actual; > - /* Whether the call was a varargs call. */ > - bool call_varargs_p; > + /* Whether EXPECTED should be treated as a lower bound. */ > + bool least_p; > } arity; > /* Information about an argument conversion mismatch. */ > struct conversion_info conversion; > @@ -628,12 +628,13 @@ alloc_rejection (enum rejection_reason_code code) > } > > static struct rejection_reason * > -arity_rejection (tree first_arg, int expected, int actual) > +arity_rejection (tree first_arg, int expected, int actual, bool least_p = false) > { > struct rejection_reason *r = alloc_rejection (rr_arity); > int adjust = first_arg != NULL_TREE; > r->u.arity.expected = expected - adjust; > r->u.arity.actual = actual - adjust; > + r->u.arity.least_p = least_p; > return r; > } > > @@ -3452,6 +3453,44 @@ add_template_candidate_real (struct z_candidate **candidates, tree tmpl, > } > gcc_assert (ia == nargs_without_in_chrg); > > + if (!obj && explicit_targs) > + { > + /* Check that there's no obvious arity mismatch before proceeding with > + deduction. This avoids substituting explicit template arguments > + into the template (which could result in an error outside the > + immediate context) when the resulting candidate would be unviable > + anyway. */ > + int min_arity = 0, max_arity = 0; > + tree parms = TYPE_ARG_TYPES (TREE_TYPE (tmpl)); > + parms = skip_artificial_parms_for (tmpl, parms); > + for (; parms != void_list_node; parms = TREE_CHAIN (parms)) > + { > + if (!parms || PACK_EXPANSION_P (TREE_VALUE (parms))) > + { > + max_arity = -1; > + break; > + } > + if (TREE_PURPOSE (parms)) > + /* A parameter with a default argument. */ > + ++max_arity; > + else > + ++min_arity, ++max_arity; > + } > + if (ia < (unsigned)min_arity) > + { > + /* Too few arguments. */ > + reason = arity_rejection (NULL_TREE, min_arity, ia, > + /*least_p=*/(max_arity == -1)); > + goto fail; > + } > + else if (max_arity != -1 && ia > (unsigned)max_arity) > + { > + /* Too many arguments. */ > + reason = arity_rejection (NULL_TREE, max_arity, ia); > + goto fail; > + } > + } > + > errs = errorcount+sorrycount; > if (!obj) > convs = alloc_conversions (nargs); > @@ -3725,12 +3764,19 @@ print_conversion_rejection (location_t loc, struct conversion_info *info, > HAVE. */ > > static void > -print_arity_information (location_t loc, unsigned int have, unsigned int want) > -{ > - inform_n (loc, want, > - " candidate expects %d argument, %d provided", > - " candidate expects %d arguments, %d provided", > - want, have); > +print_arity_information (location_t loc, unsigned int have, unsigned int want, > + bool least_p) > +{ > + if (least_p) > + inform_n (loc, want, > + " candidate expects at least %d argument, %d provided", > + " candidate expects at least %d arguments, %d provided", > + want, have); > + else > + inform_n (loc, want, > + " candidate expects %d argument, %d provided", > + " candidate expects %d arguments, %d provided", > + want, have); > } > > /* Print information about one overload candidate CANDIDATE. MSGSTR > @@ -3794,7 +3840,8 @@ print_z_candidate (location_t loc, const char *msgstr, > { > case rr_arity: > print_arity_information (cloc, r->u.arity.actual, > - r->u.arity.expected); > + r->u.arity.expected, > + r->u.arity.least_p); > break; > case rr_arg_conversion: > print_conversion_rejection (cloc, &r->u.conversion, fn); > diff --git a/gcc/testsuite/g++.dg/cpp0x/decltype29.C b/gcc/testsuite/g++.dg/cpp0x/decltype29.C > index 51da8ddd0de..ea97b033569 100644 > --- a/gcc/testsuite/g++.dg/cpp0x/decltype29.C > +++ b/gcc/testsuite/g++.dg/cpp0x/decltype29.C > @@ -10,10 +10,10 @@ ft() {} > > template<class F, int N> > decltype (ft<F> (F())) // { dg-error "depth" } > -ft() {} > +ft(F) {} > > int main() { > - ft<struct a*, 0>(); // { dg-message "from here" } > + ft<struct a*, 0>(0); // { dg-message "from here" } > } > > // { dg-prune-output "compilation terminated" } > diff --git a/gcc/testsuite/g++.dg/template/error56.C b/gcc/testsuite/g++.dg/template/error56.C > index e85471a50b0..71206a1ae5c 100644 > --- a/gcc/testsuite/g++.dg/template/error56.C > +++ b/gcc/testsuite/g++.dg/template/error56.C > @@ -3,12 +3,12 @@ > struct A > { > template <class T> void f(T); > - void f(); > + void f(int); > }; > > int main() > { > - A().f<1>(); // { dg-error "f<1>" } > + A().f<1>(0); // { dg-error "f<1>" } > // { dg-error "type/value mismatch at argument 1" "" { target *-*-* } .-1 } > // { dg-message "expected a type, got .1." "" { target *-*-* } .-2 } > } > diff --git a/gcc/testsuite/g++.dg/template/explicit-args6.C b/gcc/testsuite/g++.dg/template/explicit-args6.C > new file mode 100644 > index 00000000000..fb5e89e4cf6 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/template/explicit-args6.C > @@ -0,0 +1,33 @@ > +// PR c++/12672 > +// Verify we don't substitute explicit template arguments into > +// candidate function templates when the arity of the function > +// template disagrees with the arity of the call. > + > +template<class T> > +struct A { typedef typename T::type type; }; > + > +template<class T> void f(T); // arity 1 > +template<class T> void f(T, T, T); // arity 3 > + > +template<class T> typename A<T>::type f(T, T); // arity 2 > +template<class T, class U> typename A<T>::type f(U, U); // arity 2 > + > +struct B { > + template<class T> void f(T); // arity 1 > + template<class T> void f(T, T, T); // arity 3 > + > + template<class T> typename A<T>::type f(T, T); // arity 2 > + template<class T, class U> typename A<T>::type f(U, U); // arity 2 > +}; > + > +int main() { > + // If overload resolution attempts deduction for any of the arity-2 function > + // templates, the substitution of explicit arguments into the template would > + // cause a hard error. > + f<int>(1); > + f<int>(1, 1, 1); > + > + B b; > + b.f<int>(1); > + b.f<int>(1, 1, 1); > +} > diff --git a/gcc/testsuite/g++.old-deja/g++.pt/unify6.C b/gcc/testsuite/g++.old-deja/g++.pt/unify6.C > index d122ec2dcb9..ee14ceadd91 100644 > --- a/gcc/testsuite/g++.old-deja/g++.pt/unify6.C > +++ b/gcc/testsuite/g++.old-deja/g++.pt/unify6.C > @@ -23,8 +23,8 @@ template<class T> void foo(T const *){} // { dg-error "pointer to reference" } > > void f() > { > - foo<int &>(); // { dg-error "" } attempt to build int & const * > - foo<void ()>(); // { dg-error "" } attempt to build void (const *)() > + foo<int &>(0); // { dg-error "" } attempt to build int & const * > + foo<void ()>(0); // OK by [dcl.fct]/7, the const is silently dropped > } > > typedef void (*Fptr)(); >
diff --git a/gcc/cp/call.c b/gcc/cp/call.c index e4df72ec1a3..80e6121ce44 100644 --- a/gcc/cp/call.c +++ b/gcc/cp/call.c @@ -455,8 +455,8 @@ struct rejection_reason { int expected; /* The actual number of arguments in the call. */ int actual; - /* Whether the call was a varargs call. */ - bool call_varargs_p; + /* Whether EXPECTED should be treated as a lower bound. */ + bool least_p; } arity; /* Information about an argument conversion mismatch. */ struct conversion_info conversion; @@ -628,12 +628,13 @@ alloc_rejection (enum rejection_reason_code code) } static struct rejection_reason * -arity_rejection (tree first_arg, int expected, int actual) +arity_rejection (tree first_arg, int expected, int actual, bool least_p = false) { struct rejection_reason *r = alloc_rejection (rr_arity); int adjust = first_arg != NULL_TREE; r->u.arity.expected = expected - adjust; r->u.arity.actual = actual - adjust; + r->u.arity.least_p = least_p; return r; } @@ -3452,6 +3453,44 @@ add_template_candidate_real (struct z_candidate **candidates, tree tmpl, } gcc_assert (ia == nargs_without_in_chrg); + if (!obj && explicit_targs) + { + /* Check that there's no obvious arity mismatch before proceeding with + deduction. This avoids substituting explicit template arguments + into the template (which could result in an error outside the + immediate context) when the resulting candidate would be unviable + anyway. */ + int min_arity = 0, max_arity = 0; + tree parms = TYPE_ARG_TYPES (TREE_TYPE (tmpl)); + parms = skip_artificial_parms_for (tmpl, parms); + for (; parms != void_list_node; parms = TREE_CHAIN (parms)) + { + if (!parms || PACK_EXPANSION_P (TREE_VALUE (parms))) + { + max_arity = -1; + break; + } + if (TREE_PURPOSE (parms)) + /* A parameter with a default argument. */ + ++max_arity; + else + ++min_arity, ++max_arity; + } + if (ia < (unsigned)min_arity) + { + /* Too few arguments. */ + reason = arity_rejection (NULL_TREE, min_arity, ia, + /*least_p=*/(max_arity == -1)); + goto fail; + } + else if (max_arity != -1 && ia > (unsigned)max_arity) + { + /* Too many arguments. */ + reason = arity_rejection (NULL_TREE, max_arity, ia); + goto fail; + } + } + errs = errorcount+sorrycount; if (!obj) convs = alloc_conversions (nargs); @@ -3725,12 +3764,19 @@ print_conversion_rejection (location_t loc, struct conversion_info *info, HAVE. */ static void -print_arity_information (location_t loc, unsigned int have, unsigned int want) -{ - inform_n (loc, want, - " candidate expects %d argument, %d provided", - " candidate expects %d arguments, %d provided", - want, have); +print_arity_information (location_t loc, unsigned int have, unsigned int want, + bool least_p) +{ + if (least_p) + inform_n (loc, want, + " candidate expects at least %d argument, %d provided", + " candidate expects at least %d arguments, %d provided", + want, have); + else + inform_n (loc, want, + " candidate expects %d argument, %d provided", + " candidate expects %d arguments, %d provided", + want, have); } /* Print information about one overload candidate CANDIDATE. MSGSTR @@ -3794,7 +3840,8 @@ print_z_candidate (location_t loc, const char *msgstr, { case rr_arity: print_arity_information (cloc, r->u.arity.actual, - r->u.arity.expected); + r->u.arity.expected, + r->u.arity.least_p); break; case rr_arg_conversion: print_conversion_rejection (cloc, &r->u.conversion, fn); diff --git a/gcc/testsuite/g++.dg/cpp0x/decltype29.C b/gcc/testsuite/g++.dg/cpp0x/decltype29.C index 51da8ddd0de..ea97b033569 100644 --- a/gcc/testsuite/g++.dg/cpp0x/decltype29.C +++ b/gcc/testsuite/g++.dg/cpp0x/decltype29.C @@ -10,10 +10,10 @@ ft() {} template<class F, int N> decltype (ft<F> (F())) // { dg-error "depth" } -ft() {} +ft(F) {} int main() { - ft<struct a*, 0>(); // { dg-message "from here" } + ft<struct a*, 0>(0); // { dg-message "from here" } } // { dg-prune-output "compilation terminated" } diff --git a/gcc/testsuite/g++.dg/template/error56.C b/gcc/testsuite/g++.dg/template/error56.C index e85471a50b0..71206a1ae5c 100644 --- a/gcc/testsuite/g++.dg/template/error56.C +++ b/gcc/testsuite/g++.dg/template/error56.C @@ -3,12 +3,12 @@ struct A { template <class T> void f(T); - void f(); + void f(int); }; int main() { - A().f<1>(); // { dg-error "f<1>" } + A().f<1>(0); // { dg-error "f<1>" } // { dg-error "type/value mismatch at argument 1" "" { target *-*-* } .-1 } // { dg-message "expected a type, got .1." "" { target *-*-* } .-2 } } diff --git a/gcc/testsuite/g++.dg/template/explicit-args6.C b/gcc/testsuite/g++.dg/template/explicit-args6.C new file mode 100644 index 00000000000..fb5e89e4cf6 --- /dev/null +++ b/gcc/testsuite/g++.dg/template/explicit-args6.C @@ -0,0 +1,33 @@ +// PR c++/12672 +// Verify we don't substitute explicit template arguments into +// candidate function templates when the arity of the function +// template disagrees with the arity of the call. + +template<class T> +struct A { typedef typename T::type type; }; + +template<class T> void f(T); // arity 1 +template<class T> void f(T, T, T); // arity 3 + +template<class T> typename A<T>::type f(T, T); // arity 2 +template<class T, class U> typename A<T>::type f(U, U); // arity 2 + +struct B { + template<class T> void f(T); // arity 1 + template<class T> void f(T, T, T); // arity 3 + + template<class T> typename A<T>::type f(T, T); // arity 2 + template<class T, class U> typename A<T>::type f(U, U); // arity 2 +}; + +int main() { + // If overload resolution attempts deduction for any of the arity-2 function + // templates, the substitution of explicit arguments into the template would + // cause a hard error. + f<int>(1); + f<int>(1, 1, 1); + + B b; + b.f<int>(1); + b.f<int>(1, 1, 1); +} diff --git a/gcc/testsuite/g++.old-deja/g++.pt/unify6.C b/gcc/testsuite/g++.old-deja/g++.pt/unify6.C index d122ec2dcb9..ee14ceadd91 100644 --- a/gcc/testsuite/g++.old-deja/g++.pt/unify6.C +++ b/gcc/testsuite/g++.old-deja/g++.pt/unify6.C @@ -23,8 +23,8 @@ template<class T> void foo(T const *){} // { dg-error "pointer to reference" } void f() { - foo<int &>(); // { dg-error "" } attempt to build int & const * - foo<void ()>(); // { dg-error "" } attempt to build void (const *)() + foo<int &>(0); // { dg-error "" } attempt to build int & const * + foo<void ()>(0); // OK by [dcl.fct]/7, the const is silently dropped } typedef void (*Fptr)();