Cleanup uses of __asm__ in the runtime

[hughbe]

@gparker42

This also fixes some MSVC errors, as it doesn't define asm

[slavapestov]

As @jckarter pointed out the runtime should only be built with swift-clang, but maybe the SWIFT_SYMBOL_NAME cleanup is worth it anyway?

[hughbe]

Yeah this ones about cleaning up some uses - I think the rest of the runtime doesn't use asm but does what I've changed this to

[jckarter]

@rjmccall or @gparker42, do either of you recall why this is here? If it were intended as an optimization barrier, wouldn't it have to be volatile? As is, this would be a no-op even on Clang, AIUI.

[gparker42]

The intent is to preserve that frame in stack traces. I know the asm("") is necessary when the function is empty. This function is not empty so noinline alone may be sufficient.

[gparker42]

(If the function is empty and you use noinline without asm("") then the optimizer may simply delete the call at the call site. Technically that doesn't count as inlining. asm("") inhibits that optimization.)

[jckarter]

@swift-ci Please benchmark

[jckarter]

@swift-ci Please smoke test

[hughbe]

@jckarter do you know what I've done wrong here:

/home/buildnode/jenkins/workspace/swift-PR-Linux-smoke-test/branch-master/buildbot_linux/swift-linux-x86_64/lib/swift/linux/x86_64/libswiftCore.so: undefined reference to `ClassMirrorMetadata'
/home/buildnode/jenkins/workspace/swift-PR-Linux-smoke-test/branch-master/buildbot_linux/swift-linux-x86_64/lib/swift/linux/x86_64/libswiftCore.so: undefined reference to `MetatypeMirrorMetadata'
/home/buildnode/jenkins/workspace/swift-PR-Linux-smoke-test/branch-master/buildbot_linux/swift-linux-x86_64/lib/swift/linux/x86_64/libswiftCore.so: undefined reference to `EnumMirrorMetadata'

It seems like it's ignoring the macro and just trying to reference the macro's name... Hmm

[jckarter]

I think we want the asm names. Macros aren't namespaced and lead to problems when you try to refer to something else with the same name. We should make them obviously macros with SWIFT_PREFIXED_ALL_CAPS names, if we must, but I think MSVC has a similar feature to control symbol names.

[jckarter]

Or you could use a reference declaration to alias the symbol instead of a macro:

extern const Foo SWIFT_MANGLED_NAME(...);
static constexpr auto &ReadableName = SWIFT_MANGLED_NAME(...);

[hughbe]

@swift-ci please smoke test

[hughbe]

@swift-ci please smoke test

[jckarter]

This LGTM, thanks @hughbe!