[diamondlovesyou]

> Why is cooperation unlikely? AFAIK it’s not too hard to make a compiler support a function attribute that says “do not optimize this function at all”

Compilers like Clang actually generate terrible code; it's expected that a sufficiently smart optimizer (of which LLVM is a member) will clean it up anyway, so Clang makes no attempt to generate good code. Rust is similar. For example, a simple for-loop's induction variable is stored/loaded to an alloca (ie stack) on every use, it isn't an SSA variable. So one of the first things in the optimization pipeline is to promote those to SSA registers/variables. Disabling that would cost a ton of perf just right there, nevermind the impact on instruction combining/value tracking/scalar evolution, and crypto is pretty perf sensitive after security.

BTW, Clang/LLVM already has such a function-level attribute, `optnone`, which was actually added to support LTO. But it's all or nothing; LLVM IR/Clang doesn't have the info needed to know what instructions are timing sensitive.