[PATCH] D137107: Allow MS extension: support of constexpr with __declspec(dllimport).

[Eli Friedman via Phabricator via cfe-commits]

efriedma added inline comments.


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Comment at: clang/lib/CodeGen/CGExprConstant.cpp:1926
+            DiagnosticsEngine &Diags = CGM.getContext().getDiagnostics();
+            Diags.Report(diag::warn_for_global_ctor_for_dllimport) << D;
+            return nullptr;
----------------
I think this will trigger in cases we don't actually want it to; we only want to warn when we actually generate a global constructor, not when we end up falling back to generated code within a function.  (For example, we sometimes constant-evaluate local variables.)


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Comment at: clang/lib/CodeGen/CodeGenModule.cpp:5006
+    if (NeedsGlobalCtor || NeedsGlobalDtor)
+      DelayedCXXInitPosition[D] = ~0U;
+  } else {
----------------
zahiraam wrote:
> efriedma wrote:
> > zahiraam wrote:
> > > efriedma wrote:
> > > > zahiraam wrote:
> > > > > Do you agree this should be done only when one of those flags is on?
> > > > Yes, that's fine; I wasn't really paying close attention to the exact code.  Just wanted to make the point about the structure of the if statements, and code was the easiest way to explain it.
> > > > 
> > > > Maybe the outer if statement should actually be `if (isStaticInit(D, getLangOpts()) && NeedsGlobalCtor) {`.
> > > > 
> > > > On a related note, we might want to avoid the name "ctor", in case that accidentally conflicts with some user code; an "__"-prefixed name would be appropriate.
> > > >> Maybe the outer if statement should actually be if (isStaticInit(D, getLangOpts()) && NeedsGlobalCtor) {
> > > Not sure about that! There are cases where (isStaticInit(D, getLangOpts())) = true and NeedsGlobalCtor=false, but NeedsGlobalDtor=true. In which case a __dtor needs to be emitted, no?
> > > 
> > > Writing the condition as you are proposing would actually not get me into the body to emit the __dtor. Is that what we want?
> > EmitCXXGlobalVarDeclInitFunc should be able to handle that case.
> > 
> > Looking again, I'm a little concerned that in the isStaticInit() case, we're skipping a bunch of the logic in EmitCXXGlobalVarDeclInitFunc. EmitCXXCtorInit handles the basic cases correctly, but there are a lot of special cases in EmitCXXGlobalVarDeclInitFunc.
> I have left the condition as it was to make sure no cases are left. What other cases are you thinking of? 
> 
EmitCXXGlobalVarDeclInitFunc has special cases for CUDA, OpenMP, thread-local variables, the InitSeg attribute, and inline variables.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D137107/new/

https://reviews.llvm.org/D137107