[Bug target/115362] wrong sign caused by substraction operand swap of two dot product operands

[jondaniel879 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115362

--- Comment #24 from Jon Daniel <jondaniel879 at gmail dot com> ---
The C++ analog is the difference between std::reduce and std::accumulate but
for sub operands.