[PATCH] D55229: [COFF] Statically link certain runtime library functions

[Saleem Abdulrasool via Phabricator via cfe-commits]

compnerd added inline comments.


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Comment at: CodeGen/CodeGenModule.cpp:2957-2958
           !getCodeGenOpts().LTOVisibilityPublicStd &&
-          !getTriple().isWindowsGNUEnvironment()) {
+          !getTriple().isWindowsGNUEnvironment() &&
+          !getTriple().isWindowsMSVCEnvironment()) {
         const FunctionDecl *FD = GetRuntimeFunctionDecl(Context, Name);
----------------
rnk wrote:
> compnerd wrote:
> > rnk wrote:
> > > The condition here of `T.isOSBinFormatCOFF() && !T.isWindowsGNUEnvironment() && !T.isWindowsMSVCEnvironment()` is essentially equivalent to `T.isWindowsItaniumEnvironment()`. Please simplify the condition to that. The other relevant environments are Cygnus for Cygwin and CoreCLR, which probably want to follow the MSVC/GNU behavior.
> > IIRC, one of the issues was that lldb couldn't deal very well with the thunks.  The other thing is that there is a small penalty for something that we know that we are going to redirect through.  However, I think that if lldb is able to deal with the thunks now, I would be okay with the penalty to make the behavior more similar to MSVC.  Basically, if lldb works, lets just get rid of the special behavior for the itanium environment.
> Can you elaborate on what didn't work in LLDB when the thunks were present? What kind of functionality did you have to exercise to get it to misbehave?
Sure, it was single stepping through an indirected function call.  It would put you into the thunk rather than the destination.


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Comment at: CodeGenObjC/gnu-init.m:103
+// Make sure we do not have dllimport on the load function
+// CHECK-WIN: declare dso_local void @__objc_load
 
----------------
rnk wrote:
> compnerd wrote:
> > rnk wrote:
> > > mgrang wrote:
> > > > I had to remove dllimport in this and the next unit test. I am not sure of the wider implications of this change. Maybe controlling this via a flag (like -flto-visibility-public-std) is a better/more localized option?
> > > These are the ones that I think @compnerd really cares about since the objc runtime is typically dynamically linked and frequently called. We might want to arrange things such that we have a separate codepath for ObjC runtime helpers. I'm surprised we don't already have such a code path.
> > I think that @theraven would care more about this code path than I.  I think that this change may be wrong, because the load here is supposed to be in the ObjC runtime, and this becoming local to the module would break the global registration.
> We just set dso_local whenever something isn't dllimport, even if it's a lie sometimes. I think everything would work as intended with a linker thunk. It's "true" as far as LLVM is concerned for the purposes of emitting relocations.
Ah, okay, then, this might be okay.  However, the use of `dllimport` here would force that the runtime to be called.  Then again it is possible to statically link ...


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D55229/new/

https://reviews.llvm.org/D55229