Decouple dllexport/dllimport from linkage

Representing dllexport/dllimport as distinct linkage types prevents using
these attributes on templates and inline functions.

Instead of introducing further mixed linkage types to include linkonce and
weak ODR, the old import/export linkage types are replaced with a new
separate visibility-like specifier:

  define available_externally dllimport void @f() {}
  @Var = dllexport global i32 1, align 4

Linkage for dllexported globals and functions is now equal to their linkage
without dllexport. Imported globals and functions must be either
declarations with external linkage, or definitions with
AvailableExternallyLinkage.

llvm-svn: 199218

1 files changed, 5 insertions, 7 deletions

diff --git a/llvm/lib/Linker/LinkModules.cpp b/llvm/lib/Linker/LinkModules.cpp
index 8f2200e4ea2..4d039eb2c6d 100644
--- a/llvm/lib/Linker/LinkModules.cpp
+++ b/llvm/lib/Linker/LinkModules.cpp
@@ -543,8 +543,8 @@ bool ModuleLinker::getLinkageResult(GlobalValue *Dest, const GlobalValue *Src,
   if (SrcIsDeclaration) {
     // If Src is external or if both Src & Dest are external..  Just link the
     // external globals, we aren't adding anything.
-    if (Src->hasDLLImportLinkage()) {
-      // If one of GVs has DLLImport linkage, result should be dllimport'ed.
+    if (Src->hasDLLImportStorageClass()) {
+      // If one of GVs is marked as DLLImport, result should be dllimport'ed.
       if (DestIsDeclaration) {
         LinkFromSrc = true;
         LT = Src->getLinkage();
@@ -557,7 +557,7 @@ bool ModuleLinker::getLinkageResult(GlobalValue *Dest, const GlobalValue *Src,
       LinkFromSrc = false;
       LT = Dest->getLinkage();
     }
-  } else if (DestIsDeclaration && !Dest->hasDLLImportLinkage()) {
+  } else if (DestIsDeclaration && !Dest->hasDLLImportStorageClass()) {
     // If Dest is external but Src is not:
     LinkFromSrc = true;
     LT = Src->getLinkage();
@@ -584,10 +584,8 @@ bool ModuleLinker::getLinkageResult(GlobalValue *Dest, const GlobalValue *Src,
       LT = GlobalValue::ExternalLinkage;
     }
   } else {
-    assert((Dest->hasExternalLinkage()  || Dest->hasDLLImportLinkage() ||
-            Dest->hasDLLExportLinkage() || Dest->hasExternalWeakLinkage()) &&
-           (Src->hasExternalLinkage()   || Src->hasDLLImportLinkage() ||
-            Src->hasDLLExportLinkage()  || Src->hasExternalWeakLinkage()) &&
+    assert((Dest->hasExternalLinkage()  || Dest->hasExternalWeakLinkage()) &&
+           (Src->hasExternalLinkage()   || Src->hasExternalWeakLinkage()) &&
            "Unexpected linkage type!");
     return emitError("Linking globals named '" + Src->getName() +
                  "': symbol multiply defined!");