This is the same issue as PR86429, just in potential_constant_expression_1
rather than cxx_eval_constant_expression. As in that case, when we're
trying to evaluate a constant expression within a lambda, we don't have a
constant closure object to refer to, but we can try to refer directly to the
captured variable.
Tested x86_64-pc-linux-gnu, applying to trunk.
gcc/cp/ChangeLog
2020-05-05 Jason Merrill <ja...@redhat.com>
PR c++/90212
* constexpr.c (potential_constant_expression_1): In a lambda
function, consider a captured variable directly.
---
gcc/cp/constexpr.c | 8 +++++++-
.../g++.dg/cpp0x/lambda/lambda-constexpr2.C | 13 +++++++++++++
2 files changed, 20 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/lambda/lambda-constexpr2.C
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 637cb746576..706d8a13d8e 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -7520,12 +7520,18 @@ potential_constant_expression_1 (tree t, bool
want_rval, bool strict, bool now,
variable with automatic storage duration defined outside that
lambda-expression, where the reference would be an
odr-use. */
+
+ if (want_rval)
+ /* Since we're doing an lvalue-rvalue conversion, this might
+ not be an odr-use, so evaluate the variable directly. */
+ return RECUR (DECL_CAPTURED_VARIABLE (t), rval);
+
if (flags & tf_error)
{
tree cap = DECL_CAPTURED_VARIABLE (t);
error ("lambda capture of %qE is not a constant expression",
cap);
- if (!want_rval && decl_constant_var_p (cap))
+ if (decl_constant_var_p (cap))
inform (input_location, "because it is used as a glvalue");
}
return false;
diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-constexpr2.C
b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-constexpr2.C
new file mode 100644
index 00000000000..b1982ab0506
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-constexpr2.C
@@ -0,0 +1,13 @@
+// PR c++/90212
+// { dg-do compile { target c++11 } }
+
+template<typename T> struct tuple {
+ constexpr tuple(T&& t) : t(t) { }
+ int t;
+};
+
+void foo() {
+ constexpr tuple<int> v1{1};
+ constexpr auto v2 = v1;
+ [&]{ constexpr auto v2 = v1; };
+}
base-commit: d0aed8d5ba77e0756f3c9ebcd65eba1bfb11f24b
--
2.18.1
