Tested x86_64-pc-linux-gnu, applying to trunk.
-- 8< --
The pack index is manifestly constant-evaluated, and the call to
maybe_constant_value needs to reflect that or we wrongly complain about
non-constant index if the evaluation uses if consteval.
gcc/cp/ChangeLog:
* semantics.cc (finish_type_pack_element): Pass mce_true to
maybe_constant_value.
gcc/testsuite/ChangeLog:
* g++.dg/cpp26/pack-indexing16.C: New test.
---
gcc/cp/semantics.cc | 2 +-
gcc/testsuite/g++.dg/cpp26/pack-indexing16.C | 16 ++++++++++++++++
2 files changed, 17 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp26/pack-indexing16.C
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index b0a5f9ad660..b390d663e24 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -5086,7 +5086,7 @@ finish_underlying_type (tree type)
static tree
finish_type_pack_element (tree idx, tree types, tsubst_flags_t complain)
{
- idx = maybe_constant_value (idx);
+ idx = maybe_constant_value (idx, NULL_TREE, mce_true);
if (TREE_CODE (idx) != INTEGER_CST || !INTEGRAL_TYPE_P (TREE_TYPE (idx)))
{
if (complain & tf_error)
diff --git a/gcc/testsuite/g++.dg/cpp26/pack-indexing16.C
b/gcc/testsuite/g++.dg/cpp26/pack-indexing16.C
new file mode 100644
index 00000000000..92ade86d06b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp26/pack-indexing16.C
@@ -0,0 +1,16 @@
+// { dg-do compile { target c++26 } }
+
+int i;
+constexpr int idx()
+{
+ if consteval { return 0; }
+ else { return i; }
+}
+
+template <int... Ns>
+int first () { return Ns...[idx()]; }
+
+int main()
+{
+ return first<0,1,2>();
+}
base-commit: 57fdc97dac1453849a76bdce265428d441a03de0
--
2.49.0
