[LLVMdev] Proposing a new 'alloca' parameter attribute to implement the Microsoft C++ ABI

Stephen Lin swlin at post.harvard.edu
Tue Jul 30 11:41:55 PDT 2013

> Right. What's the point of all the effort devoted to MSVC++ ABI
> compatibility when Clang doesn't need it for being a top-notch C++
> compiler on Windows?

I brought up a similar point a little bit earlier, too....

It seems like the only necessary condition for being a first-class
native-code development tool on Windows is to support the platform C
ABI and the subset of the C++ ABI required by COM, and that is the
most that any non-MS compiler on Windows tries to do, so I am
genuinely curious why there is so much effort being spent on the more
esoteric portions of the ABI?

As far as I understand it, the case being considered here is not
supported in COM, which constrains the types of parameter and return
values at ABI boundaries to pointers, simple C types, and some special


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