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PR c++/83273 - constexpr if allows non-constant condition

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* semantics.c (finish_if_stmt_cond): Use require_constant_expression
	rather than is_constant_expression.
	* constexpr.c (potential_constant_expression_1) [LAMBDA_EXPR]: Allow
	in C++17.

From-SVN: r255390
This commit is contained in:
Jason Merrill 2017-12-04 17:52:07 -05:00 • committed by Jason Merrill
parent f3abed16a0
commit 899ac3b800
5 changed files with 28 additions and 2 deletions
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8
gcc/cp/ChangeLog
View file

@ -1,3 +1,11 @@
2017-12-04 Jason Merrill <jason@redhat.com>
PR c++/83273 - constexpr if allows non-constant condition
* semantics.c (finish_if_stmt_cond): Use require_constant_expression
rather than is_constant_expression.
* constexpr.c (potential_constant_expression_1) [LAMBDA_EXPR]: Allow
in C++17.
2017-12-01 Jason Merrill <jason@redhat.com>
Give #include hints for <complex>.

8
gcc/cp/constexpr.c
View file

@ -5524,6 +5524,14 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
return RECUR (STMT_EXPR_STMT (t), rval);
case LAMBDA_EXPR:
if (cxx_dialect >= cxx17)
/* In C++17 lambdas can be constexpr, don't give up yet. */
return true;
else if (flags & tf_error)
error_at (loc, "lambda-expression is not a constant expression "
"before C++17");
return false;
case DYNAMIC_CAST_EXPR:
case PSEUDO_DTOR_EXPR:
case NEW_EXPR:

2
gcc/cp/semantics.c
View file

@ -731,7 +731,7 @@ finish_if_stmt_cond (tree cond, tree if_stmt)
{
cond = maybe_convert_cond (cond);
if (IF_STMT_CONSTEXPR_P (if_stmt)
&& is_constant_expression (cond)
&& require_constant_expression (cond)
&& !value_dependent_expression_p (cond))
{
cond = instantiate_non_dependent_expr (cond);

2
gcc/testsuite/g++.dg/cpp1z/constexpr-if12.C
View file

@ -7,7 +7,7 @@ struct T {
template <class MustBeTemplate>
constexpr auto bf(T t) {
if constexpr(t.foo()) {
if constexpr(t.foo()) { // { dg-error "constant expression" }
return false;
}
return true;

10
gcc/testsuite/g++.dg/cpp1z/constexpr-if13.C Normal file
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@ -0,0 +1,10 @@
// PR c++/83273
// { dg-options -std=c++17 }
int main()
{
auto d = 42;
if constexpr (d > 0) { // { dg-error "constant expression" }
return d;
}
}