https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86969
Bug ID: 86969
Summary: [Regression] ICE (in tsubst_copy) for a generic
recursive lambda
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: v.reshetnikov at gmail dot com
Target Milestone: ---
/************************* BEGIN SOURCE *************************/
auto compose = [](auto... fs) {
if constexpr (sizeof...(fs) == 0) {
return [](auto x) { return x; };
} else {
auto fn = [](auto self, auto f, auto... fs) {
if constexpr (sizeof...(fs) == 0) return f;
else return [=](auto x) {
return f(self(self, fs...)(x));
};
};
return fn(fn, fs...);
}
};
static_assert(compose(
[](auto x) { return x * 3; },
[](auto x) { return x + 1; },
[](auto x) { return x / 2; }
)(6) == 12);
/************************** END SOURCE **************************/
EXPECTED: no errors.
ACTUAL:
<source>: In instantiation of '<lambda(auto:1 ...)> [with auto:1 =
{<lambda(auto:7)>, <lambda(auto:8)>, <lambda(auto:9)>}]::<lambda(auto:3,
auto:4, auto:5 ...)> [with auto:3 = <lambda(auto:1 ...)> [with auto:1 =
{<lambda(auto:7)>, <lambda(auto:8)>, <lambda(auto:9)>}]::<lambda(auto:3,
auto:4, auto:5 ...)>; auto:4 = <lambda(auto:7)>; auto:5 = {<lambda(auto:8)>,
<lambda(auto:9)>}]':
<source>:11:18: required from '<lambda(auto:1 ...)> [with auto:1 =
{<lambda(auto:7)>, <lambda(auto:8)>, <lambda(auto:9)>}]'
<source>:19:5: required from here
<source>:8:30: internal compiler error: in tsubst_copy, at cp/pt.c:15348
8 | return f(self(self, fs...)(x));
| ~~~~^~~~~~~~~~~~~
Compiles successfully with 7.3, fails with 8.1 and newer. Compiles successfully
with Clang. Looks similar to Bug 86926, but ICE location is different.
