[clang] [llvm] __declspec(noshrinkwrap) support (PR #147397)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

As a practical matter, I don't think LLVM supports shrink-wrapping on Windows at the moment.  I mean, I guess it's something someone could theoretically look into at some point, but the interaction with unwind info is complicated.

Can we define what it means to "shrink-wrap" in a way that isn't specifically tied to the shrink-wrapping pass?  We need to define what output is legal, not how we got there.  For example, if the rule is that we aren't allowed to access non-stack memory before adjusting the stack, that could interact with late instruction scheduling.

It looks like this isn't an existing MSVC feature?  If that's the case, why are we using __declspec syntax, as opposed to modern C++ attribute syntax?

https://github.com/llvm/llvm-project/pull/147397