I have been trying to discuss the definition of i686 for Rust onto Pentium Pro, see my reasoning here: rust-lang/rust#82435 (comment) -- In the answer to this, I was told that clang implies Pentium 4 for i686. See their godbolt: https://llvm.godbolt.org/z/PP69efvfx -- This inconsistency is one of the reasons keeping the Rust team from changing the definition.

For the same reasoning as in my post, I think i686 should imply Pentium Pro, not Pentium 4. Clang is seemingly aware of this (See: https://clang.llvm.org/doxygen/Basic_2Targets_2X86_8cpp_source.html ), but it still uses a Pentium 4 cpu-target in the end for some reason.