from nightly-2021-04-26 started linking unneeded ws2_32.dll for x86_64-pc-windows-msvc target

[klensy]

For empty.rs:

fn main(){}

rustc +nightly-2021-04-25-x86_64-pc-windows-msvc empty.rs -O
don't use ws2_32.dll

 KERNEL32.dll
 VCRUNTIME140.dll
 api-ms-win-crt-runtime-l1-1-0.dll
 api-ms-win-crt-math-l1-1-0.dll
 api-ms-win-crt-stdio-l1-1-0.dll
 api-ms-win-crt-locale-l1-1-0.dll
 api-ms-win-crt-heap-l1-1-0.dll

rustc +nightly-2021-04-26-x86_64-pc-windows-msvc empty.rs -O
use ws2_32.dll

 WS2_32.dll
 KERNEL32.dll
 VCRUNTIME140.dll
 api-ms-win-crt-runtime-l1-1-0.dll
 api-ms-win-crt-math-l1-1-0.dll
 api-ms-win-crt-stdio-l1-1-0.dll
 api-ms-win-crt-locale-l1-1-0.dll
 api-ms-win-crt-heap-l1-1-0.dll

Can be checked for example via dumpbin.exe /dependents empty.exe

regressed between 42816d6...3709ae3, i'm thinking about #84115

Thing that imported from ws2_32 is WSACleanup

@rustbot label +O-windows +A-linkage

[klensy]

@CDirkx

[CDirkx]

Yeah that makes sense that it is from #84115.

rust/library/std/src/sys/windows/net.rs

Lines 44 to 51 in 40d2302

	pub fn cleanup() {
	if INIT.is_completed() {
	// only close the socket interface if it has actually been started
	unsafe {
	c::WSACleanup();
	}
	}
	}

cleanup always called, which makes Rust link to WSACleanup from ws2_32.dll, even if no networking code is ever used. I wonder if extracting WSACleanup into a seperate non-inlined function would be enough:

pub fn cleanup() { 
    // only perform cleanup if network functionality was actually initialized
    if INIT.is_completed() { 
        _cleanup();
    }
}

// avoid linking to `WSACleanup` if it is never used by letting this function to be optimized away
#[inline(never)]
fn _cleanup() {
    unsafe { 
        // close the socket interface
        c::WSACleanup();
    }
}