* [PATCH] c++: constant non-copy-init is manifestly constant [PR108243] @ 2023-02-20 19:46 Patrick Palka 2023-02-21 20:18 ` Patrick Palka 0 siblings, 1 reply; 3+ messages in thread From: Patrick Palka @ 2023-02-20 19:46 UTC (permalink / raw) To: gcc-patches; +Cc: jason, Patrick Palka According to [basic.start.static]/2 and [expr.const]/2, a variable with static storage duration initialized with a constant initializer has constant initialization, and such an initializer is manifestly constant-evaluated. We're already getting this right with copy initialization because in that case check_initializer would consistently call store_init_value (which for TREE_STATIC variables calls fold_non_dependent_init with m_c_e=true). But for direct (or default) initialization, we don't always call store_init_value. We instead however always call maybe_constant_init from expand_default_init[1], albeit with m_c_e=false which means we don't always get the "manifestly constant-evaluated" part right for copy-init. This patch fixes this by simply passing m_c_e=true to this call to maybe_constant_init for static storage duration variables, mirroring what store_init_value basically does. [1]: this maybe_constant_init call isn't reached in the copy-init case because there init is a CONSTRUCTOR rather than a TREE_LIST so expand_default_init exits early returning an INIT_EXPR. This INIT_EXPR is ultimately what causes us to consistently hit the store_init_value code path from check_initializer in the copy-init case. Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for trunk? Would it be suitable to backport this to the 12 branch since it should only affect C++20 code? PR c++/108243 gcc/cp/ChangeLog: * init.cc (expand_default_init): Pass m_c_e=true instead of =false to maybe_constant_init when initializing a variable with static storage duration. gcc/testsuite/ChangeLog: * g++.dg/cpp2a/is-constant-evaluated14.C: New test. --- gcc/cp/init.cc | 5 +- .../g++.dg/cpp2a/is-constant-evaluated14.C | 140 ++++++++++++++++++ 2 files changed, 144 insertions(+), 1 deletion(-) create mode 100644 gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated14.C diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc index 52e96fbe590..705a5b3bdb6 100644 --- a/gcc/cp/init.cc +++ b/gcc/cp/init.cc @@ -2203,7 +2203,10 @@ expand_default_init (tree binfo, tree true_exp, tree exp, tree init, int flags, tree fn = get_callee_fndecl (rval); if (fn && DECL_DECLARED_CONSTEXPR_P (fn)) { - tree e = maybe_constant_init (rval, exp); + bool manifestly_const_eval = false; + if (VAR_P (exp) && TREE_STATIC (exp)) + manifestly_const_eval = true; + tree e = maybe_constant_init (rval, exp, manifestly_const_eval); if (TREE_CONSTANT (e)) rval = cp_build_init_expr (exp, e); } diff --git a/gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated14.C b/gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated14.C new file mode 100644 index 00000000000..365bca3fd9a --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated14.C @@ -0,0 +1,140 @@ +// PR c++/108243 +// Verify a variable with static storage duration initialized with a +// constant initializer has constant initialization, and the initializer +// is manifestly constant-evaluated. +// { dg-do run { target c++11 } } +// { dg-additional-options "-fdump-tree-original" } + +#include <initializer_list> + +struct A { + constexpr A(int n) : n(n), m(__builtin_is_constant_evaluated()) { } + constexpr A() : A(42) { } + void verify_mce() const { + if (m != 1) __builtin_abort(); + } + int n; + int m; +}; + +A a1 = {42}; +A a2{42}; +A a3(42); +A a4; +A a5{}; + +void f() { + static A a1 = {42}; + static A a2{42}; + static A a3(42); + static A a4; + static A a5{}; + for (auto& a : {a1, a2, a3, a4, a5}) + a.verify_mce(); +} + +template<int... N> +void g() { + static A a1 = {42}; + static A a2{42}; + static A a3(42); + static A a4; + static A a5{}; + static A a6 = {N...}; + static A a7{N...}; + static A a8(N...); + for (auto& a : {a1, a2, a3, a4, a5, a6, a7, a8}) + a.verify_mce(); +} + +struct B { + static A a1; + static A a2; + static A a3; + static A a4; + static A a5; + static void verify_mce() { + for (auto& a : {a1, a2, a3, a4, a5}) + a.verify_mce(); + } +}; + +A B::a1 = {42}; +A B::a2{42}; +A B::a3(42); +A B::a4; +A B::a5{}; + +template<int... N> +struct BT { + static A a1; + static A a2; + static A a3; + static A a4; + static A a5; + static A a6; + static A a7; + static A a8; + static void verify_mce() { + for (auto& a : {a1, a2, a3, a4, a5}) + a.verify_mce(); + } +}; + +template<int... N> A BT<N...>::a1 = {42}; +template<int... N> A BT<N...>::a2{42}; +template<int... N> A BT<N...>::a3(42); +template<int... N> A BT<N...>::a4; +template<int... N> A BT<N...>::a5{}; +template<int... N> A BT<N...>::a6 = {N...}; +template<int... N> A BT<N...>::a7{N...}; +template<int... N> A BT<N...>::a8(N...); + +#if __cpp_inline_variables +struct BI { + static inline A a1 = {42}; + static inline A a2{42}; + static inline A a3; + static inline A a4{}; + static void verify_mce() { + for (auto& a : {a1, a2, a3, a4}) + a.verify_mce(); + } +}; + +template<int... N> +struct BIT { + static inline A a1 = {42}; + static inline A a2{42}; + static inline A a3; + static inline A a4{}; + static inline A a5 = {N...}; + static inline A a6{N...}; + static void verify_mce() { + for (auto& a : {a1, a2, a3, a4, a5, a6}) + a.verify_mce(); + } +}; +#endif + +int main() { + for (auto& a : {a1, a2, a3, a4, a5}) + a.verify_mce(); + + f(); + g<42>(); + g<>(); + + B::verify_mce(); + BT<42>::verify_mce(); + BT<>::verify_mce(); + +#if __cpp_inline_variables + BI::verify_mce(); + BIT<42>::verify_mce(); + BIT<>::verify_mce(); +#endif +} + +// { dg-final { scan-tree-dump-not "static initializers for" "original" } } +// { dg-final { scan-tree-dump-not "cxa_guard_acquire" "original" } } -- 2.39.2.501.gd9d677b2d8 ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] c++: constant non-copy-init is manifestly constant [PR108243] 2023-02-20 19:46 [PATCH] c++: constant non-copy-init is manifestly constant [PR108243] Patrick Palka @ 2023-02-21 20:18 ` Patrick Palka 2023-03-02 16:35 ` Jason Merrill 0 siblings, 1 reply; 3+ messages in thread From: Patrick Palka @ 2023-02-21 20:18 UTC (permalink / raw) To: Patrick Palka; +Cc: gcc-patches, jason On Mon, 20 Feb 2023, Patrick Palka wrote: > According to [basic.start.static]/2 and [expr.const]/2, a variable > with static storage duration initialized with a constant initializer > has constant initialization, and such an initializer is manifestly > constant-evaluated. > > We're already getting this right with copy initialization because in > that case check_initializer would consistently call store_init_value > (which for TREE_STATIC variables calls fold_non_dependent_init with > m_c_e=true). > > But for direct (or default) initialization, we don't always call > store_init_value. We instead however always call maybe_constant_init > from expand_default_init[1], albeit with m_c_e=false which means we > don't always get the "manifestly constant-evaluated" part right for > copy-init. > > This patch fixes this by simply passing m_c_e=true to this call to > maybe_constant_init for static storage duration variables, mirroring > what store_init_value basically does. > > [1]: this maybe_constant_init call isn't reached in the copy-init > case because there init is a CONSTRUCTOR rather than a TREE_LIST so > expand_default_init exits early returning an INIT_EXPR. This INIT_EXPR > is ultimately what causes us to consistently hit the store_init_value > code path from check_initializer in the copy-init case. > > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for > trunk? Would it be suitable to backport this to the 12 branch since > it should only affect C++20 code? > > PR c++/108243 > > gcc/cp/ChangeLog: > > * init.cc (expand_default_init): Pass m_c_e=true instead of > =false to maybe_constant_init when initializing a variable > with static storage duration. > > gcc/testsuite/ChangeLog: > > * g++.dg/cpp2a/is-constant-evaluated14.C: New test. > --- > gcc/cp/init.cc | 5 +- > .../g++.dg/cpp2a/is-constant-evaluated14.C | 140 ++++++++++++++++++ > 2 files changed, 144 insertions(+), 1 deletion(-) > create mode 100644 gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated14.C > > diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc > index 52e96fbe590..705a5b3bdb6 100644 > --- a/gcc/cp/init.cc > +++ b/gcc/cp/init.cc > @@ -2203,7 +2203,10 @@ expand_default_init (tree binfo, tree true_exp, tree exp, tree init, int flags, > tree fn = get_callee_fndecl (rval); > if (fn && DECL_DECLARED_CONSTEXPR_P (fn)) > { > - tree e = maybe_constant_init (rval, exp); > + bool manifestly_const_eval = false; > + if (VAR_P (exp) && TREE_STATIC (exp)) > + manifestly_const_eval = true; > + tree e = maybe_constant_init (rval, exp, manifestly_const_eval); > if (TREE_CONSTANT (e)) > rval = cp_build_init_expr (exp, e); > } Hmm, alternatively we could just override manifestly_const_eval to true from maybe_constant_init for static storage duration variables, like so. I guess this approach much be preferable since it potentially benefits all maybe_constant_init callers? -- >8 -- gcc/cp/ChangeLog: * constexpr.cc (maybe_constant_init_1): Override manifestly_const_eval to true if is_static. diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc index aa2c14355f8..8ae83a6eadf 100644 --- a/gcc/cp/constexpr.cc +++ b/gcc/cp/constexpr.cc @@ -8760,7 +8760,8 @@ maybe_constant_init_1 (tree t, tree decl, bool allow_non_constant, bool is_static = (decl && DECL_P (decl) && (TREE_STATIC (decl) || DECL_EXTERNAL (decl))); t = cxx_eval_outermost_constant_expr (t, allow_non_constant, !is_static, - mce_value (manifestly_const_eval), + (is_static ? mce_true + : mce_value (manifestly_const_eval)), false, decl); } if (TREE_CODE (t) == TARGET_EXPR) > diff --git a/gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated14.C b/gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated14.C > new file mode 100644 > index 00000000000..365bca3fd9a > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated14.C > @@ -0,0 +1,140 @@ > +// PR c++/108243 > +// Verify a variable with static storage duration initialized with a > +// constant initializer has constant initialization, and the initializer > +// is manifestly constant-evaluated. > +// { dg-do run { target c++11 } } > +// { dg-additional-options "-fdump-tree-original" } > + > +#include <initializer_list> > + > +struct A { > + constexpr A(int n) : n(n), m(__builtin_is_constant_evaluated()) { } > + constexpr A() : A(42) { } > + void verify_mce() const { > + if (m != 1) __builtin_abort(); > + } > + int n; > + int m; > +}; > + > +A a1 = {42}; > +A a2{42}; > +A a3(42); > +A a4; > +A a5{}; > + > +void f() { > + static A a1 = {42}; > + static A a2{42}; > + static A a3(42); > + static A a4; > + static A a5{}; > + for (auto& a : {a1, a2, a3, a4, a5}) > + a.verify_mce(); > +} > + > +template<int... N> > +void g() { > + static A a1 = {42}; > + static A a2{42}; > + static A a3(42); > + static A a4; > + static A a5{}; > + static A a6 = {N...}; > + static A a7{N...}; > + static A a8(N...); > + for (auto& a : {a1, a2, a3, a4, a5, a6, a7, a8}) > + a.verify_mce(); > +} > + > +struct B { > + static A a1; > + static A a2; > + static A a3; > + static A a4; > + static A a5; > + static void verify_mce() { > + for (auto& a : {a1, a2, a3, a4, a5}) > + a.verify_mce(); > + } > +}; > + > +A B::a1 = {42}; > +A B::a2{42}; > +A B::a3(42); > +A B::a4; > +A B::a5{}; > + > +template<int... N> > +struct BT { > + static A a1; > + static A a2; > + static A a3; > + static A a4; > + static A a5; > + static A a6; > + static A a7; > + static A a8; > + static void verify_mce() { > + for (auto& a : {a1, a2, a3, a4, a5}) > + a.verify_mce(); > + } > +}; > + > +template<int... N> A BT<N...>::a1 = {42}; > +template<int... N> A BT<N...>::a2{42}; > +template<int... N> A BT<N...>::a3(42); > +template<int... N> A BT<N...>::a4; > +template<int... N> A BT<N...>::a5{}; > +template<int... N> A BT<N...>::a6 = {N...}; > +template<int... N> A BT<N...>::a7{N...}; > +template<int... N> A BT<N...>::a8(N...); > + > +#if __cpp_inline_variables > +struct BI { > + static inline A a1 = {42}; > + static inline A a2{42}; > + static inline A a3; > + static inline A a4{}; > + static void verify_mce() { > + for (auto& a : {a1, a2, a3, a4}) > + a.verify_mce(); > + } > +}; > + > +template<int... N> > +struct BIT { > + static inline A a1 = {42}; > + static inline A a2{42}; > + static inline A a3; > + static inline A a4{}; > + static inline A a5 = {N...}; > + static inline A a6{N...}; > + static void verify_mce() { > + for (auto& a : {a1, a2, a3, a4, a5, a6}) > + a.verify_mce(); > + } > +}; > +#endif > + > +int main() { > + for (auto& a : {a1, a2, a3, a4, a5}) > + a.verify_mce(); > + > + f(); > + g<42>(); > + g<>(); > + > + B::verify_mce(); > + BT<42>::verify_mce(); > + BT<>::verify_mce(); > + > +#if __cpp_inline_variables > + BI::verify_mce(); > + BIT<42>::verify_mce(); > + BIT<>::verify_mce(); > +#endif > +} > + > +// { dg-final { scan-tree-dump-not "static initializers for" "original" } } > +// { dg-final { scan-tree-dump-not "cxa_guard_acquire" "original" } } > -- > 2.39.2.501.gd9d677b2d8 > > ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] c++: constant non-copy-init is manifestly constant [PR108243] 2023-02-21 20:18 ` Patrick Palka @ 2023-03-02 16:35 ` Jason Merrill 0 siblings, 0 replies; 3+ messages in thread From: Jason Merrill @ 2023-03-02 16:35 UTC (permalink / raw) To: Patrick Palka; +Cc: gcc-patches On 2/21/23 15:18, Patrick Palka wrote: > On Mon, 20 Feb 2023, Patrick Palka wrote: > >> According to [basic.start.static]/2 and [expr.const]/2, a variable >> with static storage duration initialized with a constant initializer >> has constant initialization, and such an initializer is manifestly >> constant-evaluated. >> >> We're already getting this right with copy initialization because in >> that case check_initializer would consistently call store_init_value >> (which for TREE_STATIC variables calls fold_non_dependent_init with >> m_c_e=true). >> >> But for direct (or default) initialization, we don't always call >> store_init_value. We instead however always call maybe_constant_init >> from expand_default_init[1], albeit with m_c_e=false which means we >> don't always get the "manifestly constant-evaluated" part right for >> copy-init. >> >> This patch fixes this by simply passing m_c_e=true to this call to >> maybe_constant_init for static storage duration variables, mirroring >> what store_init_value basically does. >> >> [1]: this maybe_constant_init call isn't reached in the copy-init >> case because there init is a CONSTRUCTOR rather than a TREE_LIST so >> expand_default_init exits early returning an INIT_EXPR. This INIT_EXPR >> is ultimately what causes us to consistently hit the store_init_value >> code path from check_initializer in the copy-init case. >> >> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for >> trunk? Would it be suitable to backport this to the 12 branch since >> it should only affect C++20 code? >> >> PR c++/108243 >> >> gcc/cp/ChangeLog: >> >> * init.cc (expand_default_init): Pass m_c_e=true instead of >> =false to maybe_constant_init when initializing a variable >> with static storage duration. >> >> gcc/testsuite/ChangeLog: >> >> * g++.dg/cpp2a/is-constant-evaluated14.C: New test. >> --- >> gcc/cp/init.cc | 5 +- >> .../g++.dg/cpp2a/is-constant-evaluated14.C | 140 ++++++++++++++++++ >> 2 files changed, 144 insertions(+), 1 deletion(-) >> create mode 100644 gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated14.C >> >> diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc >> index 52e96fbe590..705a5b3bdb6 100644 >> --- a/gcc/cp/init.cc >> +++ b/gcc/cp/init.cc >> @@ -2203,7 +2203,10 @@ expand_default_init (tree binfo, tree true_exp, tree exp, tree init, int flags, >> tree fn = get_callee_fndecl (rval); >> if (fn && DECL_DECLARED_CONSTEXPR_P (fn)) >> { >> - tree e = maybe_constant_init (rval, exp); >> + bool manifestly_const_eval = false; >> + if (VAR_P (exp) && TREE_STATIC (exp)) >> + manifestly_const_eval = true; >> + tree e = maybe_constant_init (rval, exp, manifestly_const_eval); >> if (TREE_CONSTANT (e)) >> rval = cp_build_init_expr (exp, e); >> } > > Hmm, alternatively we could just override manifestly_const_eval to true > from maybe_constant_init for static storage duration variables, like so. > I guess this approach much be preferable since it potentially benefits > all maybe_constant_init callers? That does look better. OK (perhaps with a local variable to hold the mce_value). > -- >8 -- > > gcc/cp/ChangeLog: > > * constexpr.cc (maybe_constant_init_1): Override > manifestly_const_eval to true if is_static. > > diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc > index aa2c14355f8..8ae83a6eadf 100644 > --- a/gcc/cp/constexpr.cc > +++ b/gcc/cp/constexpr.cc > @@ -8760,7 +8760,8 @@ maybe_constant_init_1 (tree t, tree decl, bool allow_non_constant, > bool is_static = (decl && DECL_P (decl) > && (TREE_STATIC (decl) || DECL_EXTERNAL (decl))); > t = cxx_eval_outermost_constant_expr (t, allow_non_constant, !is_static, > - mce_value (manifestly_const_eval), > + (is_static ? mce_true > + : mce_value (manifestly_const_eval)), > false, decl); > } > if (TREE_CODE (t) == TARGET_EXPR) > >> diff --git a/gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated14.C b/gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated14.C >> new file mode 100644 >> index 00000000000..365bca3fd9a >> --- /dev/null >> +++ b/gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated14.C >> @@ -0,0 +1,140 @@ >> +// PR c++/108243 >> +// Verify a variable with static storage duration initialized with a >> +// constant initializer has constant initialization, and the initializer >> +// is manifestly constant-evaluated. >> +// { dg-do run { target c++11 } } >> +// { dg-additional-options "-fdump-tree-original" } >> + >> +#include <initializer_list> >> + >> +struct A { >> + constexpr A(int n) : n(n), m(__builtin_is_constant_evaluated()) { } >> + constexpr A() : A(42) { } >> + void verify_mce() const { >> + if (m != 1) __builtin_abort(); >> + } >> + int n; >> + int m; >> +}; >> + >> +A a1 = {42}; >> +A a2{42}; >> +A a3(42); >> +A a4; >> +A a5{}; >> + >> +void f() { >> + static A a1 = {42}; >> + static A a2{42}; >> + static A a3(42); >> + static A a4; >> + static A a5{}; >> + for (auto& a : {a1, a2, a3, a4, a5}) >> + a.verify_mce(); >> +} >> + >> +template<int... N> >> +void g() { >> + static A a1 = {42}; >> + static A a2{42}; >> + static A a3(42); >> + static A a4; >> + static A a5{}; >> + static A a6 = {N...}; >> + static A a7{N...}; >> + static A a8(N...); >> + for (auto& a : {a1, a2, a3, a4, a5, a6, a7, a8}) >> + a.verify_mce(); >> +} >> + >> +struct B { >> + static A a1; >> + static A a2; >> + static A a3; >> + static A a4; >> + static A a5; >> + static void verify_mce() { >> + for (auto& a : {a1, a2, a3, a4, a5}) >> + a.verify_mce(); >> + } >> +}; >> + >> +A B::a1 = {42}; >> +A B::a2{42}; >> +A B::a3(42); >> +A B::a4; >> +A B::a5{}; >> + >> +template<int... N> >> +struct BT { >> + static A a1; >> + static A a2; >> + static A a3; >> + static A a4; >> + static A a5; >> + static A a6; >> + static A a7; >> + static A a8; >> + static void verify_mce() { >> + for (auto& a : {a1, a2, a3, a4, a5}) >> + a.verify_mce(); >> + } >> +}; >> + >> +template<int... N> A BT<N...>::a1 = {42}; >> +template<int... N> A BT<N...>::a2{42}; >> +template<int... N> A BT<N...>::a3(42); >> +template<int... N> A BT<N...>::a4; >> +template<int... N> A BT<N...>::a5{}; >> +template<int... N> A BT<N...>::a6 = {N...}; >> +template<int... N> A BT<N...>::a7{N...}; >> +template<int... N> A BT<N...>::a8(N...); >> + >> +#if __cpp_inline_variables >> +struct BI { >> + static inline A a1 = {42}; >> + static inline A a2{42}; >> + static inline A a3; >> + static inline A a4{}; >> + static void verify_mce() { >> + for (auto& a : {a1, a2, a3, a4}) >> + a.verify_mce(); >> + } >> +}; >> + >> +template<int... N> >> +struct BIT { >> + static inline A a1 = {42}; >> + static inline A a2{42}; >> + static inline A a3; >> + static inline A a4{}; >> + static inline A a5 = {N...}; >> + static inline A a6{N...}; >> + static void verify_mce() { >> + for (auto& a : {a1, a2, a3, a4, a5, a6}) >> + a.verify_mce(); >> + } >> +}; >> +#endif >> + >> +int main() { >> + for (auto& a : {a1, a2, a3, a4, a5}) >> + a.verify_mce(); >> + >> + f(); >> + g<42>(); >> + g<>(); >> + >> + B::verify_mce(); >> + BT<42>::verify_mce(); >> + BT<>::verify_mce(); >> + >> +#if __cpp_inline_variables >> + BI::verify_mce(); >> + BIT<42>::verify_mce(); >> + BIT<>::verify_mce(); >> +#endif >> +} >> + >> +// { dg-final { scan-tree-dump-not "static initializers for" "original" } } >> +// { dg-final { scan-tree-dump-not "cxa_guard_acquire" "original" } } >> -- >> 2.39.2.501.gd9d677b2d8 >> >> > ^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2023-03-02 16:35 UTC | newest] Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2023-02-20 19:46 [PATCH] c++: constant non-copy-init is manifestly constant [PR108243] Patrick Palka 2023-02-21 20:18 ` Patrick Palka 2023-03-02 16:35 ` Jason Merrill
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