[llvm-dev] Disabling inline compilation (Clang with VS2019)

[John Emmas via llvm-dev]

On 23/09/2021 14:50, Hans Wennborg wrote:
> extern int __declspec(dllimport) x;
> inline int __declspec(dllimport) get_x() { return x; }
> int f() { return get_x(); }
>
> int __declspec(dllimport) foo();
> inline int __declspec(dllimport) bar() { return foo(); }
> int g() { return bar(); }
>
> MSVC 19.21 will inline the get_x() and bar() calls, but 19.22 will
> not: https://godbolt.org/z/n1cedv3a8
>
> Clang matches the 19.21 behaviour. The way it checks whether a
> dllimport function is safe to inline is whether it only references
> symbols which are also dllimport (the logic lives in
> CodeGenModule::shouldEmitFunction()).
>
> It seems that MSVC has become more conservative here. We could update
> Clang to behave similarly, but it would be good to understand the
> exact motivation.
>

Many thanks for the contributions here.  I often post on the MS 
Developer forum so I'll ask for clarification there - and I'll post back 
if I get any replies (though bear in mind that replies can sometimes 
take a long time there!!)

I've used MSVC for maybe 20 years and I've never once known a DLL 
function to be inline-able. So my guess (though it is just a guess) is 
that something maybe went awry in 19.21 and then got corrected in 
19.22.  Best regards,

John