[llvm-bugs] [Bug 48557] New: Parallel algorithms fail to enforce Mandates: requirements

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=48557

            Bug ID: 48557
           Summary: Parallel algorithms fail to enforce Mandates:
                    requirements
           Product: parallel STL
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: New
          Assignee: ldionne at apple.com
          Reporter: zilla at kayari.org
                CC: llvm-bugs at lists.llvm.org

For example:

Mandates: All of
 — binary_op(init, init),
 — binary_op(init, unary_op(*first)),
 — binary_op(unary_op(*first), init), and
 — binary_op(unary_op(*first), unary_op(*first))
are convertible to T.

This was stated with "Requires:" in C++17, but in C++20 violating the
requirement must be diagnosed.

Example:

#include <numeric>
#include <execution>

int main() {
  int a[]{ 1 };

  auto r = std::transform_reduce(
      std::execution::seq, a, a+1, 0,
      [](int& a, int b) {
        return a + b;
      },
      [](int i) { return i; });
}

This compiles without error using GCC's copy of the PSTL code.

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