https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100295
Bug ID: 100295
Summary: Internal compiler error from generic lambda capturing
parameter pack and expanding it in if constexpr
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: davidfromonline at gmail dot com
Target Milestone: ---
The following well-formed translation unit
```
template<typename... Ts>
void f(Ts... ts) {
auto lambda = [=](auto x) {
if constexpr (sizeof((..., ts), x) != 0) {
(..., ts);
}
};
lambda(0);
}
void g() {
f(0);
}
```
causes gcc to crash with
```
<source>: In instantiation of ‘f<int>(int)::<lambda(auto:1)> [with auto:1 =
int]’:
<source>:8:8: required from ‘void f(Ts ...) [with Ts = {int}]’
<source>:12:3: required from here
<source>:5:31: internal compiler error: trying to capture ‘ts#0’ in
instantiation of generic lambda
5 | (..., ts);
| ^~
0x9c9318 add_capture(tree_node*, tree_node*, tree_node*, bool, bool)
../../source/gcc/cp/lambda.c:637
0x9c9391 add_default_capture(tree_node*, tree_node*, tree_node*)
../../source/gcc/cp/lambda.c:697
0xaa68ef tsubst_copy_and_build(tree_node*, tree_node*, int, tree_node*, bool,
bool)
../../source/gcc/cp/pt.c:20834
0xaa3ea8 tsubst_copy_and_build(tree_node*, tree_node*, int, tree_node*, bool,
bool)
../../source/gcc/cp/pt.c:20949
0xaaf3d7 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
../../source/gcc/cp/pt.c:19204
0xaae9d1 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
../../source/gcc/cp/pt.c:18229
0xaae9d1 gen_elem_of_pack_expansion_instantiation
../../source/gcc/cp/pt.c:12568
0xaae9d1 tsubst_pack_expansion(tree_node*, tree_node*, int, tree_node*)
../../source/gcc/cp/pt.c:13233
0xaa163f tsubst_fold_expr_pack
../../source/gcc/cp/pt.c:12646
0xaa163f tsubst_unary_left_fold
../../source/gcc/cp/pt.c:12685
0xaa163f tsubst_copy
../../source/gcc/cp/pt.c:17343
0xaa56f2 tsubst_copy_and_build(tree_node*, tree_node*, int, tree_node*, bool,
bool)
../../source/gcc/cp/pt.c:20962
0xaaf3d7 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
../../source/gcc/cp/pt.c:19204
0xab11f9 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
../../source/gcc/cp/pt.c:18274
0xab0aa3 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
../../source/gcc/cp/pt.c:18595
0xab4503 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
../../source/gcc/cp/pt.c:18564
0xab0aa3 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
../../source/gcc/cp/pt.c:18595
0xab0aa3 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
../../source/gcc/cp/pt.c:18595
0xab8308 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
../../source/gcc/cp/pt.c:18229
0xab8308 instantiate_body
../../source/gcc/cp/pt.c:25921
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
Compiler returned: 1
```
