| Message ID | 20220915180312.1596193-1-ppalka@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | c++: 'mutable' within constexpr [PR92505] | expand |
On 9/15/22 14:03, Patrick Palka wrote: > This patch permits accessing 'mutable' members of local objects during > constexpr evaluation (which other compilers seem to accept in C++14 > mode, while we reject), while continuing to reject it for global objects > (as in the last line of cpp0x/constexpr-mutable1.C, which other > compilers also reject). To distinguish between the two cases, it looks > like we just need to additionally check CONSTRUCTOR_MUTABLE_POISION > alongside DECL_MUTABLE_P in cxx_eval_component_reference before > rejecting the access. > > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for > trunk? OK. > PR c++/92505 > > gcc/cp/ChangeLog: > > * constexpr.cc (cxx_eval_component_reference): Test non_constant_p > earlier. In C++14 or later, reject DECL_MUTABLE_P member > accesses only if CONSTRUCTOR_MUTABLE_POISION is also set. > > gcc/testsuite/ChangeLog: > > * g++.dg/cpp0x/constexpr-mutable3.C: New test. > * g++.dg/cpp1y/constexpr-mutable1.C: New test. > --- > gcc/cp/constexpr.cc | 11 +++++++---- > gcc/testsuite/g++.dg/cpp0x/constexpr-mutable3.C | 7 +++++++ > gcc/testsuite/g++.dg/cpp1y/constexpr-mutable1.C | 16 ++++++++++++++++ > 3 files changed, 30 insertions(+), 4 deletions(-) > create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-mutable3.C > create mode 100644 gcc/testsuite/g++.dg/cpp1y/constexpr-mutable1.C > > diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc > index 57283eabf3c..10639876d9c 100644 > --- a/gcc/cp/constexpr.cc > +++ b/gcc/cp/constexpr.cc > @@ -4088,6 +4088,8 @@ cxx_eval_component_reference (const constexpr_ctx *ctx, tree t, > tree whole = cxx_eval_constant_expression (ctx, orig_whole, > lval, > non_constant_p, overflow_p); > + if (*non_constant_p) > + return t; > if (INDIRECT_REF_P (whole) > && integer_zerop (TREE_OPERAND (whole, 0))) > { > @@ -4108,20 +4110,21 @@ cxx_eval_component_reference (const constexpr_ctx *ctx, tree t, > whole, part, NULL_TREE); > /* Don't VERIFY_CONSTANT here; we only want to check that we got a > CONSTRUCTOR. */ > - if (!*non_constant_p && TREE_CODE (whole) != CONSTRUCTOR) > + if (TREE_CODE (whole) != CONSTRUCTOR) > { > if (!ctx->quiet) > error ("%qE is not a constant expression", orig_whole); > *non_constant_p = true; > + return t; > } > - if (DECL_MUTABLE_P (part)) > + if ((cxx_dialect < cxx14 || CONSTRUCTOR_MUTABLE_POISON (whole)) > + && DECL_MUTABLE_P (part)) > { > if (!ctx->quiet) > error ("mutable %qD is not usable in a constant expression", part); > *non_constant_p = true; > + return t; > } > - if (*non_constant_p) > - return t; > bool pmf = TYPE_PTRMEMFUNC_P (TREE_TYPE (whole)); > FOR_EACH_CONSTRUCTOR_ELT (CONSTRUCTOR_ELTS (whole), i, field, value) > { > diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-mutable3.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-mutable3.C > new file mode 100644 > index 00000000000..46c9d8437be > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-mutable3.C > @@ -0,0 +1,7 @@ > +// PR c++/92505 > +// { dg-do compile { target c++11 } } > + > +struct A { mutable int m; }; > +constexpr int f(A a) { return a.m; } > +static_assert(f({42}) == 42, ""); > +// { dg-error "non-constant|mutable" "" { target c++11_only } .-1 } > diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-mutable1.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-mutable1.C > new file mode 100644 > index 00000000000..6c47988c01a > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-mutable1.C > @@ -0,0 +1,16 @@ > +// PR c++/92505 > +// { dg-do compile { target c++14 } } > + > +struct S { mutable int m; }; > + > +static_assert(S{42}.m == 42, ""); > + > +constexpr int f() { > + S s = {40}; > + s.m++; > + const auto& cs = s; > + ++cs.m; > + return cs.m; > +} > + > +static_assert(f() == 42, "");
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc index 57283eabf3c..10639876d9c 100644 --- a/gcc/cp/constexpr.cc +++ b/gcc/cp/constexpr.cc @@ -4088,6 +4088,8 @@ cxx_eval_component_reference (const constexpr_ctx *ctx, tree t, tree whole = cxx_eval_constant_expression (ctx, orig_whole, lval, non_constant_p, overflow_p); + if (*non_constant_p) + return t; if (INDIRECT_REF_P (whole) && integer_zerop (TREE_OPERAND (whole, 0))) { @@ -4108,20 +4110,21 @@ cxx_eval_component_reference (const constexpr_ctx *ctx, tree t, whole, part, NULL_TREE); /* Don't VERIFY_CONSTANT here; we only want to check that we got a CONSTRUCTOR. */ - if (!*non_constant_p && TREE_CODE (whole) != CONSTRUCTOR) + if (TREE_CODE (whole) != CONSTRUCTOR) { if (!ctx->quiet) error ("%qE is not a constant expression", orig_whole); *non_constant_p = true; + return t; } - if (DECL_MUTABLE_P (part)) + if ((cxx_dialect < cxx14 || CONSTRUCTOR_MUTABLE_POISON (whole)) + && DECL_MUTABLE_P (part)) { if (!ctx->quiet) error ("mutable %qD is not usable in a constant expression", part); *non_constant_p = true; + return t; } - if (*non_constant_p) - return t; bool pmf = TYPE_PTRMEMFUNC_P (TREE_TYPE (whole)); FOR_EACH_CONSTRUCTOR_ELT (CONSTRUCTOR_ELTS (whole), i, field, value) { diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-mutable3.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-mutable3.C new file mode 100644 index 00000000000..46c9d8437be --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-mutable3.C @@ -0,0 +1,7 @@ +// PR c++/92505 +// { dg-do compile { target c++11 } } + +struct A { mutable int m; }; +constexpr int f(A a) { return a.m; } +static_assert(f({42}) == 42, ""); +// { dg-error "non-constant|mutable" "" { target c++11_only } .-1 } diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-mutable1.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-mutable1.C new file mode 100644 index 00000000000..6c47988c01a --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-mutable1.C @@ -0,0 +1,16 @@ +// PR c++/92505 +// { dg-do compile { target c++14 } } + +struct S { mutable int m; }; + +static_assert(S{42}.m == 42, ""); + +constexpr int f() { + S s = {40}; + s.m++; + const auto& cs = s; + ++cs.m; + return cs.m; +} + +static_assert(f() == 42, "");