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