================
@@ -0,0 +1,50 @@
+// RUN: %clang_cc1 -std=c++26 -triple x86_64-linux-gnu -emit-llvm -o - %s |
FileCheck %s
+
+// static constexpr structured binding pack elements used as array
+// subscript indices must be constant-folded at the Clang codegen level.
+// Without the fix, each element is emitted as a load from a "reference
+// temporary" static variable.
+
+namespace std {
+ using size_t = decltype(sizeof(0));
+ template <typename T> struct tuple_size;
+ template <size_t I, typename T> struct tuple_element;
+} // namespace std
+
+using u8 = unsigned char;
+
+template <u8 N>
+struct Range {
+ template <std::size_t I>
+ consteval friend u8 get(Range) noexcept { return I; }
+};
+
+namespace std {
+ template <u8 N>
+ struct tuple_size<Range<N>> { static constexpr std::size_t value = N; };
+ template <std::size_t I, u8 N>
+ struct tuple_element<I, Range<N>> { using type = u8; };
+} // namespace std
+
+template <std::size_t N>
+struct Array {
+ u8 data[N];
+ constexpr const u8 &operator[](std::size_t i) const { return data[i]; }
+};
+
+template <std::size_t L, std::size_t R>
+__attribute__((always_inline)) inline constexpr Array<L + R>
+concat(const Array<L> &l, const Array<R> &r) {
+ static constexpr auto [...I] = Range<L>{};
+ static constexpr auto [...J] = Range<R>{};
+ return {{l[I]..., r[J]...}};
+}
+
+Array<32> test(const Array<16> &l, const Array<16> &r) {
+ return concat(l, r);
+}
+
+// The binding-pack indices must not be materialised as "reference temporary"
+// static variables at any optimisation level.
+// CHECK-LABEL: define {{.*}} @{{.*test.*}}
+// CHECK-NOT: reference temporary
----------------
Takashiidobe wrote:
I implemented what I think is your suggested change in CodeGenModule. It turns
some globals to constants in other tests. As well I also took your test instead
of the one from the issue since the issue's program emits a lot of LLVM IR for
each of the temporaries whereas this one is pretty small, just one temporary
which is either global or const. The test now asserts that the reference
temporary is const instead of global which makes writing the assertions easier.
https://github.com/llvm/llvm-project/pull/186594
_______________________________________________
cfe-commits mailing list
[email protected]
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
