[PATCH] D36487: Emit section information for extern variables.

[Elizabeth Andrews via Phabricator via cfe-commits]

eandrews added inline comments.


================
Comment at: lib/CodeGen/CodeGenModule.cpp:2434
+    // Emit section information for extern variables.
+    if (D->hasExternalStorage() && !D->isThisDeclarationADefinition()) {
+      if (const SectionAttr *SA = D->getAttr<SectionAttr>())
----------------
efriedma wrote:
> eandrews wrote:
> > efriedma wrote:
> > > Why do you specifically check "D->hasExternalStorage() && !D->isThisDeclarationADefinition()", instead of just setting the section unconditionally?
> > I noticed that you enter GetOrCreateLLVMGlobal( ) whenever the extern variable is declared as well as when it is defined. The flow of the program is different in each case. When the variable is defined, it also enters EmitGlobalVarDefinition( ). There is existing code handling section information here. I added the check in GetOrCreateLLVMGlobal( ) so the block gets skipped for variable definition, since its already handled elsewhere.
> I would rather just call setSection unconditionally here, as opposed to trying to guess whether the global will eventually be defined.
> 
> I'm also sort of concerned the behavior here could be weird if a section attribute is added on a redeclaration (e.g. what happens if you write `extern int x; int y = &x; extern int x __attribute((section("foo")));`)... maybe we should emit a warning?
@efriedma  I modified the patch to emit a warning in the scenario you mentioned. A warning is also emitted for the following - 

```extern int x;  int *y=&x; int x __attribute__((section("foo"))); 
```
I thought it made sense to emit the warning for the latter as well. Should I restrict the warning to just redeclarations (without definition) instead?


https://reviews.llvm.org/D36487