| Message ID | 20220420224003.374946-1-polacek@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | c++: wrong error with constexpr COMPOUND_EXPR [PR105321] | expand |
On 4/20/22 18:40, Marek Polacek wrote: > Here we issue a bogus error for the first assert in the test. Therein > we have > > <retval> = (void) (VIEW_CONVERT_EXPR<bool>(yes) || handle_error ());, VIEW_CONVERT_EXPR<int>(value); > > which has a COMPOUND_EXPR, so we get to cxx_eval_constant_expression > <case COMPOUND_EXPR>. The problem here is that we call > > 7044 /* Check that the LHS is constant and then discard it. */ > 7045 cxx_eval_constant_expression (ctx, op0, > 7046 true, non_constant_p, overflow_p, > 7047 jump_target); > > where lval is always true, so the PARM_DECL 'yes' is not evaluated into > its value. r218832 changed the argument for 'lval' from false to true: > > (cxx_eval_constant_expression) [COMPOUND_EXPR]: Pass true for lval. > > but I think we want to pass 'lval' instead. Jakub tells me that's what > we do for "(void) expr" as well. [expr.comma] says that the left expression > is a discarded-value expression, but [expr.context] doesn't suggest that > we should always be passing false for lval as pre-r218832. In a discarded-value expression, we don't do the lvalue-rvalue conversion; whether we want an lvalue for the RHS of the comma is irrelevant. The bug here seems to be that we aren't doing the l->r conversion for the LHS of the TRUTH_OR_EXPR; I'd think that cxx_eval_logical_expression should pass false for lval to both recursive calls, there's no case where we actually expect an lvalue from a TRUTH_*. > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/11.3? > > PR c++/105321 > > gcc/cp/ChangeLog: > > * constexpr.cc (cxx_eval_constant_expression) <case COMPOUND_EXPR>: Pass > lval to cxx_eval_constant_expression. > > gcc/testsuite/ChangeLog: > > * g++.dg/cpp0x/constexpr-105321.C: New test. > --- > gcc/cp/constexpr.cc | 2 +- > gcc/testsuite/g++.dg/cpp0x/constexpr-105321.C | 18 ++++++++++++++++++ > 2 files changed, 19 insertions(+), 1 deletion(-) > create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-105321.C > > diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc > index e89440e770f..28271d4405d 100644 > --- a/gcc/cp/constexpr.cc > +++ b/gcc/cp/constexpr.cc > @@ -7043,7 +7043,7 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t, > { > /* Check that the LHS is constant and then discard it. */ > cxx_eval_constant_expression (ctx, op0, > - true, non_constant_p, overflow_p, > + lval, non_constant_p, overflow_p, > jump_target); > if (*non_constant_p) > return t; > diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-105321.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-105321.C > new file mode 100644 > index 00000000000..adb6830ff22 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-105321.C > @@ -0,0 +1,18 @@ > +// PR c++/105321 > +// { dg-do compile { target c++11 } } > + > +bool handle_error(); > + > +constexpr int echo(int value, bool yes = true) noexcept > +{ > + return (yes || handle_error()), value; > +} > + > +static_assert(echo(10) == 10, ""); > + > +constexpr int echo2(int value, bool no = false) noexcept > +{ > + return (!no || handle_error()), value; > +} > + > +static_assert(echo2(10) == 10, ""); > > base-commit: 5bde80f48bcc594658c788895ad1fd86d0916fc2
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc index e89440e770f..28271d4405d 100644 --- a/gcc/cp/constexpr.cc +++ b/gcc/cp/constexpr.cc @@ -7043,7 +7043,7 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t, { /* Check that the LHS is constant and then discard it. */ cxx_eval_constant_expression (ctx, op0, - true, non_constant_p, overflow_p, + lval, non_constant_p, overflow_p, jump_target); if (*non_constant_p) return t; diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-105321.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-105321.C new file mode 100644 index 00000000000..adb6830ff22 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-105321.C @@ -0,0 +1,18 @@ +// PR c++/105321 +// { dg-do compile { target c++11 } } + +bool handle_error(); + +constexpr int echo(int value, bool yes = true) noexcept +{ + return (yes || handle_error()), value; +} + +static_assert(echo(10) == 10, ""); + +constexpr int echo2(int value, bool no = false) noexcept +{ + return (!no || handle_error()), value; +} + +static_assert(echo2(10) == 10, "");