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: 199204

1 files changed, 13 insertions, 9 deletions

diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index 9e150e85756..d8e5c89598e 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -421,16 +421,12 @@ void Verifier::visitGlobalValue(GlobalValue &GV) {
   Assert1(!GV.isDeclaration() ||
           GV.isMaterializable() ||
           GV.hasExternalLinkage() ||
-          GV.hasDLLImportLinkage() ||
           GV.hasExternalWeakLinkage() ||
           (isa<GlobalAlias>(GV) &&
            (GV.hasLocalLinkage() || GV.hasWeakLinkage())),
-  "Global is external, but doesn't have external or dllimport or weak linkage!",
+          "Global is external, but doesn't have external or weak linkage!",
           &GV);
 
-  Assert1(!GV.hasDLLImportLinkage() || GV.isDeclaration(),
-          "Global is marked as dllimport, but not external", &GV);
-
   Assert1(!GV.hasAppendingLinkage() || isa<GlobalVariable>(GV),
           "Only global variables can have appending linkage!", &GV);
 
@@ -456,8 +452,7 @@ void Verifier::visitGlobalVariable(GlobalVariable &GV) {
               &GV);
     }
   } else {
-    Assert1(GV.hasExternalLinkage() || GV.hasDLLImportLinkage() ||
-            GV.hasExternalWeakLinkage(),
+    Assert1(GV.hasExternalLinkage() || GV.hasExternalWeakLinkage(),
             "invalid linkage type for global declaration", &GV);
   }
 
@@ -502,6 +497,11 @@ void Verifier::visitGlobalVariable(GlobalVariable &GV) {
     }
   }
 
+  Assert1(!GV.hasDLLImportStorageClass() ||
+          (GV.isDeclaration() && GV.hasExternalLinkage()) ||
+          GV.hasAvailableExternallyLinkage(),
+          "Global is marked as dllimport, but not external", &GV);
+
   if (!GV.hasInitializer()) {
     visitGlobalValue(GV);
     return;
@@ -1078,8 +1078,7 @@ void Verifier::visitFunction(Function &F) {
   if (F.isMaterializable()) {
     // Function has a body somewhere we can't see.
   } else if (F.isDeclaration()) {
-    Assert1(F.hasExternalLinkage() || F.hasDLLImportLinkage() ||
-            F.hasExternalWeakLinkage(),
+    Assert1(F.hasExternalLinkage() || F.hasExternalWeakLinkage(),
             "invalid linkage type for function declaration", &F);
   } else {
     // Verify that this function (which has a body) is not named "llvm.*".  It
@@ -1105,6 +1104,11 @@ void Verifier::visitFunction(Function &F) {
     if (F.hasAddressTaken(&U))
       Assert1(0, "Invalid user of intrinsic instruction!", U);
   }
+
+  Assert1(!F.hasDLLImportStorageClass() ||
+          (F.isDeclaration() && F.hasExternalLinkage()) ||
+          F.hasAvailableExternallyLinkage(),
+          "Function is marked as dllimport, but not external.", &F);
 }
 
 // verifyBasicBlock - Verify that a basic block is well formed...