cbe9891b44
Resolves: https://github.com/llvm/llvm-project/issues/164150 C++26 allows for constexpr packs in structured bindings. This is a new feature (the code doesn't compile on lower the -std=c++26) and so was previously unhandled in clang. This makes clang aware of packs and handle them as one constant unit instead of materializing them as separate mutable reference temporaries allowing llvm to optimize them. This turns the example code from the issue into this as you would expect without compiling for zen 5 (the good codegen described). ```asm movq %rdi, %rax movups (%rsi), %xmm0 movups %xmm0, (%rdi) movups (%rdx), %xmm0 movups %xmm0, 16(%rdi) retq ```
41 lines
1020 B
C++
41 lines
1020 B
C++
// RUN: %clang_cc1 -std=c++26 -triple x86_64-linux-gnu -emit-llvm -o - %s | FileCheck %s
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namespace std {
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using size_t = decltype(sizeof(0));
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template <typename T> struct tuple_size;
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template <size_t I, typename T> struct tuple_element;
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template <typename T> struct tuple_size<const T> : tuple_size<T> {};
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template <size_t I, typename T> struct tuple_element<I, const T> {
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using type = const typename tuple_element<I, T>::type;
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};
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} // namespace std
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using u8 = unsigned char;
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template <u8 N> struct Range {
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template <std::size_t I>
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constexpr friend u8 get(Range) noexcept {
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return I;
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}
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};
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namespace std {
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template <u8 N> struct tuple_size<Range<N>> {
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static constexpr std::size_t value = N;
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};
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template <std::size_t I, u8 N> struct tuple_element<I, Range<N>> {
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using type = u8;
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};
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} // namespace std
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const u8 &f() {
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static constexpr auto [I] = Range<1>();
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return I;
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}
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// CHECK: @[[TMP:_ZGR.*]] = internal constant i8 0, align 1
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// CHECK-LABEL: define {{.*}} @_Z1fv(
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// CHECK: ret ptr @[[TMP]]
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