Early in Win32 development, the x86 calling convention was __cdecl. I did all the work to change it to __stdcall (callee clean-up). Yes, it was done purely for performance reasons. It was a huge change to the codebase and as a side-effect turned up a lot of "interesting" code which relied on cdecl calling conventions.

Good times.

For 32 bit yes, although IIRC x64 convention is caller clean-up.

That's why I said 32-bit Win32 :-)