Message ID | 20230303175121.705791-1-polacek@redhat.com |
---|---|
State | New |
Headers | show |
Series | c++: error with constexpr operator() [PR107939] | expand |
On 3/3/23 12:51, Marek Polacek wrote: > Similarly to PR107938, this also started with r11-557, whereby cp_finish_decl > can call check_initializer even in a template for a constexpr initializer. > > Here we are rejecting > > extern const Q q; > > template<int> > constexpr auto p = q(0); > > even though q has a constexpr operator(). It's deemed non-const by > decl_maybe_constant_var_p because even though 'q' is const it is not > of integral/enum type. I think the fix is for p_c_e to treat q(0) as > potentially-constant, as below. > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/12? > > PR c++/107939 > > gcc/cp/ChangeLog: > > * constexpr.cc (is_constexpr_function_object): New. > (potential_constant_expression_1): Treat an object with constexpr > operator() as potentially-constant. > > gcc/testsuite/ChangeLog: > > * g++.dg/cpp1y/var-templ74.C: Remove dg-error. > * g++.dg/cpp1y/var-templ77.C: New test. > --- > gcc/cp/constexpr.cc | 23 ++++++++++++++++++++++- > gcc/testsuite/g++.dg/cpp1y/var-templ74.C | 2 +- > gcc/testsuite/g++.dg/cpp1y/var-templ77.C | 14 ++++++++++++++ > 3 files changed, 37 insertions(+), 2 deletions(-) > create mode 100644 gcc/testsuite/g++.dg/cpp1y/var-templ77.C > > diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc > index acf9847a4d1..7d786f332b4 100644 > --- a/gcc/cp/constexpr.cc > +++ b/gcc/cp/constexpr.cc > @@ -8929,6 +8929,24 @@ check_for_return_continue (tree *tp, int *walk_subtrees, void *data) > return NULL_TREE; > } > > +/* Return true iff TYPE is a class with constexpr operator(). */ > + > +static bool > +is_constexpr_function_object (tree type) > +{ > + if (!CLASS_TYPE_P (type)) > + return false; > + > + for (tree f = TYPE_FIELDS (type); f; f = DECL_CHAIN (f)) > + if (TREE_CODE (f) == FUNCTION_DECL > + && DECL_OVERLOADED_OPERATOR_P (f) > + && DECL_OVERLOADED_OPERATOR_IS (f, CALL_EXPR) > + && DECL_DECLARED_CONSTEXPR_P (f)) > + return true; > + > + return false; > +} > + > /* Return true if T denotes a potentially constant expression. Issue > diagnostic as appropriate under control of FLAGS. If WANT_RVAL is true, > an lvalue-rvalue conversion is implied. If NOW is true, we want to > @@ -9160,7 +9178,10 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now, > } > else if (fun) > { > - if (RECUR (fun, rval)) > + if (VAR_P (fun) > + && is_constexpr_function_object (TREE_TYPE (fun))) > + /* Could be an object with constexpr operator(). */; I guess if fun is not a function pointer, we don't know if we're using it as an lvalue or rvalue, so we want to pass 'any' for want_rval, which should make this work; I don't think we need to be specific about constexpr op(), as a constexpr conversion operator to fn* could also do the trick. > + else if (RECUR (fun, rval)) > /* Might end up being a constant function pointer. */; > else > return false; > diff --git a/gcc/testsuite/g++.dg/cpp1y/var-templ74.C b/gcc/testsuite/g++.dg/cpp1y/var-templ74.C > index 4e2e800a6eb..c76a7d949ac 100644 > --- a/gcc/testsuite/g++.dg/cpp1y/var-templ74.C > +++ b/gcc/testsuite/g++.dg/cpp1y/var-templ74.C > @@ -9,7 +9,7 @@ struct Q { > extern const Q q; > > template<int> > -constexpr const Q* p = q(0); // { dg-bogus "not usable" "PR107939" { xfail *-*-* } } > +constexpr const Q* p = q(0); > > void > g () > diff --git a/gcc/testsuite/g++.dg/cpp1y/var-templ77.C b/gcc/testsuite/g++.dg/cpp1y/var-templ77.C > new file mode 100644 > index 00000000000..b480f54b001 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp1y/var-templ77.C > @@ -0,0 +1,14 @@ > +// PR c++/107939 > +// { dg-do compile { target c++14 } } > + > +struct Q { > + struct P { > + const Q* p; > + }; > + int n; > + constexpr P operator()(int) const { return {this}; } > +}; > + > +extern const Q q; > +template<int> > +constexpr auto p = q(0); > > base-commit: 9056d0df830c5a295d7594d517d409d10476990d
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc index acf9847a4d1..7d786f332b4 100644 --- a/gcc/cp/constexpr.cc +++ b/gcc/cp/constexpr.cc @@ -8929,6 +8929,24 @@ check_for_return_continue (tree *tp, int *walk_subtrees, void *data) return NULL_TREE; } +/* Return true iff TYPE is a class with constexpr operator(). */ + +static bool +is_constexpr_function_object (tree type) +{ + if (!CLASS_TYPE_P (type)) + return false; + + for (tree f = TYPE_FIELDS (type); f; f = DECL_CHAIN (f)) + if (TREE_CODE (f) == FUNCTION_DECL + && DECL_OVERLOADED_OPERATOR_P (f) + && DECL_OVERLOADED_OPERATOR_IS (f, CALL_EXPR) + && DECL_DECLARED_CONSTEXPR_P (f)) + return true; + + return false; +} + /* Return true if T denotes a potentially constant expression. Issue diagnostic as appropriate under control of FLAGS. If WANT_RVAL is true, an lvalue-rvalue conversion is implied. If NOW is true, we want to @@ -9160,7 +9178,10 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now, } else if (fun) { - if (RECUR (fun, rval)) + if (VAR_P (fun) + && is_constexpr_function_object (TREE_TYPE (fun))) + /* Could be an object with constexpr operator(). */; + else if (RECUR (fun, rval)) /* Might end up being a constant function pointer. */; else return false; diff --git a/gcc/testsuite/g++.dg/cpp1y/var-templ74.C b/gcc/testsuite/g++.dg/cpp1y/var-templ74.C index 4e2e800a6eb..c76a7d949ac 100644 --- a/gcc/testsuite/g++.dg/cpp1y/var-templ74.C +++ b/gcc/testsuite/g++.dg/cpp1y/var-templ74.C @@ -9,7 +9,7 @@ struct Q { extern const Q q; template<int> -constexpr const Q* p = q(0); // { dg-bogus "not usable" "PR107939" { xfail *-*-* } } +constexpr const Q* p = q(0); void g () diff --git a/gcc/testsuite/g++.dg/cpp1y/var-templ77.C b/gcc/testsuite/g++.dg/cpp1y/var-templ77.C new file mode 100644 index 00000000000..b480f54b001 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1y/var-templ77.C @@ -0,0 +1,14 @@ +// PR c++/107939 +// { dg-do compile { target c++14 } } + +struct Q { + struct P { + const Q* p; + }; + int n; + constexpr P operator()(int) const { return {this}; } +}; + +extern const Q q; +template<int> +constexpr auto p = q(0);