* [PATCH] c++: error with constexpr operator() [PR107939] @ 2023-03-03 17:51 Marek Polacek 2023-03-06 16:12 ` Jason Merrill 0 siblings, 1 reply; 5+ messages in thread From: Marek Polacek @ 2023-03-03 17:51 UTC (permalink / raw) To: Jason Merrill, GCC Patches 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(). */; + 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 -- 2.39.2 ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] c++: error with constexpr operator() [PR107939] 2023-03-03 17:51 [PATCH] c++: error with constexpr operator() [PR107939] Marek Polacek @ 2023-03-06 16:12 ` Jason Merrill 2023-03-06 22:01 ` [PATCH v2] " Marek Polacek 0 siblings, 1 reply; 5+ messages in thread From: Jason Merrill @ 2023-03-06 16:12 UTC (permalink / raw) To: Marek Polacek, GCC Patches 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 ^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH v2] c++: error with constexpr operator() [PR107939] 2023-03-06 16:12 ` Jason Merrill @ 2023-03-06 22:01 ` Marek Polacek 2023-03-07 14:53 ` Jason Merrill 0 siblings, 1 reply; 5+ messages in thread From: Marek Polacek @ 2023-03-06 22:01 UTC (permalink / raw) To: Jason Merrill; +Cc: GCC Patches On Mon, Mar 06, 2023 at 11:12:56AM -0500, Jason Merrill wrote: > 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 Presumably the operator function could return this, making it an lvalue? I'm not sure I'm really clear on this. > , so we want to pass 'any' for want_rval, which should > make this work; Yes, want_rval==false means that p_c_e/VAR_DECL will not issue the hard error. > I don't think we need to be specific about constexpr op(), > as a constexpr conversion operator to fn* could also do the trick. Ah, those surrogate classes. I couldn't reproduce the problem with them, though I'm adding a test for it anyway. Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? -- >8 -- 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. If fun is not a function pointer, we don't know if we're using it as an lvalue or rvalue, so with this patch we pass 'any' for want_rval. With that, p_c_e/VAR_DECL doesn't flat out reject the underlying VAR_DECL. PR c++/107939 gcc/cp/ChangeLog: * constexpr.cc (potential_constant_expression_1) <case CALL_EXPR>: Pass 'any' when recursing on a VAR_DECL and not a pointer to function. gcc/testsuite/ChangeLog: * g++.dg/cpp1y/var-templ74.C: Remove dg-error. * g++.dg/cpp1y/var-templ77.C: New test. --- gcc/cp/constexpr.cc | 8 ++++-- gcc/testsuite/g++.dg/cpp1y/var-templ74.C | 2 +- gcc/testsuite/g++.dg/cpp1y/var-templ77.C | 32 ++++++++++++++++++++++++ 3 files changed, 39 insertions(+), 3 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 364695b762c..3079561f2e8 100644 --- a/gcc/cp/constexpr.cc +++ b/gcc/cp/constexpr.cc @@ -9179,8 +9179,12 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now, } else if (fun) { - if (RECUR (fun, rval)) - /* Might end up being a constant function pointer. */; + if (RECUR (fun, FUNCTION_POINTER_TYPE_P (fun) ? rval : any)) + /* Might end up being a constant function pointer. But it + could also be a function object with constexpr op(), so + we pass 'any' so that the underlying VAR_DECL is deemed + as potentially-constant even though it wasn't declared + constexpr. */; 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..0c56d70a034 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1y/var-templ77.C @@ -0,0 +1,32 @@ +// 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); +static_assert(p<0>.p == &q, ""); + +constexpr int +fn (int) +{ + return 42; +} + +struct Sur { + using FN = int(int); + constexpr operator FN*() const { return &fn; } +}; + +extern const Sur sur; +template<int> +constexpr int aja = sur (0); +static_assert(aja<0> == 42, ""); +static_assert(sur(1) == 42, ""); base-commit: 553ff2524f412be4e02e2ffb1a0a3dc3e2280742 -- 2.39.2 ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2] c++: error with constexpr operator() [PR107939] 2023-03-06 22:01 ` [PATCH v2] " Marek Polacek @ 2023-03-07 14:53 ` Jason Merrill 2023-03-07 15:11 ` Marek Polacek 0 siblings, 1 reply; 5+ messages in thread From: Jason Merrill @ 2023-03-07 14:53 UTC (permalink / raw) To: Marek Polacek; +Cc: GCC Patches On 3/6/23 17:01, Marek Polacek wrote: > On Mon, Mar 06, 2023 at 11:12:56AM -0500, Jason Merrill wrote: >> 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 > > Presumably the operator function could return this, making it an lvalue? > I'm not sure I'm really clear on this. I mean just calling the operator uses the variable as an lvalue, by passing its address as 'this'. >> , so we want to pass 'any' for want_rval, which should >> make this work; > > Yes, want_rval==false means that p_c_e/VAR_DECL will not issue the > hard error. > >> I don't think we need to be specific about constexpr op(), >> as a constexpr conversion operator to fn* could also do the trick. > > Ah, those surrogate classes. I couldn't reproduce the problem with > them, though I'm adding a test for it anyway. > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? OK, thanks. > -- >8 -- > 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. > > If fun is not a function pointer, we don't know if we're using it as an > lvalue or rvalue, so with this patch we pass 'any' for want_rval. With > that, p_c_e/VAR_DECL doesn't flat out reject the underlying VAR_DECL. > > PR c++/107939 > > gcc/cp/ChangeLog: > > * constexpr.cc (potential_constant_expression_1) <case CALL_EXPR>: Pass > 'any' when recursing on a VAR_DECL and not a pointer to function. > > gcc/testsuite/ChangeLog: > > * g++.dg/cpp1y/var-templ74.C: Remove dg-error. > * g++.dg/cpp1y/var-templ77.C: New test. > --- > gcc/cp/constexpr.cc | 8 ++++-- > gcc/testsuite/g++.dg/cpp1y/var-templ74.C | 2 +- > gcc/testsuite/g++.dg/cpp1y/var-templ77.C | 32 ++++++++++++++++++++++++ > 3 files changed, 39 insertions(+), 3 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 364695b762c..3079561f2e8 100644 > --- a/gcc/cp/constexpr.cc > +++ b/gcc/cp/constexpr.cc > @@ -9179,8 +9179,12 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now, > } > else if (fun) > { > - if (RECUR (fun, rval)) > - /* Might end up being a constant function pointer. */; > + if (RECUR (fun, FUNCTION_POINTER_TYPE_P (fun) ? rval : any)) > + /* Might end up being a constant function pointer. But it > + could also be a function object with constexpr op(), so > + we pass 'any' so that the underlying VAR_DECL is deemed > + as potentially-constant even though it wasn't declared > + constexpr. */; > 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..0c56d70a034 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp1y/var-templ77.C > @@ -0,0 +1,32 @@ > +// 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); > +static_assert(p<0>.p == &q, ""); > + > +constexpr int > +fn (int) > +{ > + return 42; > +} > + > +struct Sur { > + using FN = int(int); > + constexpr operator FN*() const { return &fn; } > +}; > + > +extern const Sur sur; > +template<int> > +constexpr int aja = sur (0); > +static_assert(aja<0> == 42, ""); > +static_assert(sur(1) == 42, ""); > > base-commit: 553ff2524f412be4e02e2ffb1a0a3dc3e2280742 ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2] c++: error with constexpr operator() [PR107939] 2023-03-07 14:53 ` Jason Merrill @ 2023-03-07 15:11 ` Marek Polacek 0 siblings, 0 replies; 5+ messages in thread From: Marek Polacek @ 2023-03-07 15:11 UTC (permalink / raw) To: Jason Merrill; +Cc: GCC Patches On Tue, Mar 07, 2023 at 09:53:28AM -0500, Jason Merrill wrote: > On 3/6/23 17:01, Marek Polacek wrote: > > On Mon, Mar 06, 2023 at 11:12:56AM -0500, Jason Merrill wrote: > > > 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 > > > > Presumably the operator function could return this, making it an lvalue? > > I'm not sure I'm really clear on this. > > I mean just calling the operator uses the variable as an lvalue, by passing > its address as 'this'. Ah yeah, right. Unless there's the && ref-qual etc. > > > , so we want to pass 'any' for want_rval, which should > > > make this work; > > > > Yes, want_rval==false means that p_c_e/VAR_DECL will not issue the > > hard error. > > > > > I don't think we need to be specific about constexpr op(), > > > as a constexpr conversion operator to fn* could also do the trick. > > > > Ah, those surrogate classes. I couldn't reproduce the problem with > > them, though I'm adding a test for it anyway. > > > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? > > OK, thanks. Thanks. Marek ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2023-03-07 15:11 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2023-03-03 17:51 [PATCH] c++: error with constexpr operator() [PR107939] Marek Polacek 2023-03-06 16:12 ` Jason Merrill 2023-03-06 22:01 ` [PATCH v2] " Marek Polacek 2023-03-07 14:53 ` Jason Merrill 2023-03-07 15:11 ` Marek Polacek
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