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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199218 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 29 insertions, 17 deletions

diff --git a/lib/IR/AsmWriter.cpp b/lib/IR/AsmWriter.cpp
index 91684c9c70..eba05c5f28 100644
--- a/lib/IR/AsmWriter.cpp
+++ b/lib/IR/AsmWriter.cpp
@@ -1367,8 +1367,6 @@ static void PrintLinkage(GlobalValue::LinkageTypes LT,
   case GlobalValue::WeakODRLinkage:       Out << "weak_odr ";       break;
   case GlobalValue::CommonLinkage:        Out << "common ";         break;
   case GlobalValue::AppendingLinkage:     Out << "appending ";      break;
-  case GlobalValue::DLLImportLinkage:     Out << "dllimport ";      break;
-  case GlobalValue::DLLExportLinkage:     Out << "dllexport ";      break;
   case GlobalValue::ExternalWeakLinkage:  Out << "extern_weak ";    break;
   case GlobalValue::AvailableExternallyLinkage:
     Out << "available_externally ";
@@ -1386,6 +1384,15 @@ static void PrintVisibility(GlobalValue::VisibilityTypes Vis,
   }
 }
 
+static void PrintDLLStorageClass(GlobalValue::DLLStorageClassTypes SCT,
+                                 formatted_raw_ostream &Out) {
+  switch (SCT) {
+  case GlobalValue::DefaultStorageClass: break;
+  case GlobalValue::DLLImportStorageClass: Out << "dllimport "; break;
+  case GlobalValue::DLLExportStorageClass: Out << "dllexport "; break;
+  }
+}
+
 static void PrintThreadLocalModel(GlobalVariable::ThreadLocalMode TLM,
                                   formatted_raw_ostream &Out) {
   switch (TLM) {
@@ -1418,6 +1425,7 @@ void AssemblyWriter::printGlobal(const GlobalVariable *GV) {
 
   PrintLinkage(GV->getLinkage(), Out);
   PrintVisibility(GV->getVisibility(), Out);
+  PrintDLLStorageClass(GV->getDLLStorageClass(), Out);
   PrintThreadLocalModel(GV->getThreadLocalMode(), Out);
 
   if (unsigned AddressSpace = GV->getType()->getAddressSpace())
@@ -1455,6 +1463,7 @@ void AssemblyWriter::printAlias(const GlobalAlias *GA) {
     Out << " = ";
   }
   PrintVisibility(GA->getVisibility(), Out);
+  PrintDLLStorageClass(GA->getDLLStorageClass(), Out);
 
   Out << "alias ";
 
@@ -1552,6 +1561,7 @@ void AssemblyWriter::printFunction(const Function *F) {
 
   PrintLinkage(F->getLinkage(), Out);
   PrintVisibility(F->getVisibility(), Out);
+  PrintDLLStorageClass(F->getDLLStorageClass(), Out);
 
   // Print the calling convention.
   if (F->getCallingConv() != CallingConv::C) {
diff --git a/lib/IR/Core.cpp b/lib/IR/Core.cpp
index ff4976bcbf..6e920a2daa 100644
--- a/lib/IR/Core.cpp
+++ b/lib/IR/Core.cpp
@@ -1164,10 +1164,6 @@ LLVMLinkage LLVMGetLinkage(LLVMValueRef Global) {
     return LLVMLinkerPrivateLinkage;
   case GlobalValue::LinkerPrivateWeakLinkage:
     return LLVMLinkerPrivateWeakLinkage;
-  case GlobalValue::DLLImportLinkage:
-    return LLVMDLLImportLinkage;
-  case GlobalValue::DLLExportLinkage:
-    return LLVMDLLExportLinkage;
   case GlobalValue::ExternalWeakLinkage:
     return LLVMExternalWeakLinkage;
   case GlobalValue::CommonLinkage:
@@ -1219,10 +1215,12 @@ void LLVMSetLinkage(LLVMValueRef Global, LLVMLinkage Linkage) {
     GV->setLinkage(GlobalValue::LinkerPrivateWeakLinkage);
     break;
   case LLVMDLLImportLinkage:
-    GV->setLinkage(GlobalValue::DLLImportLinkage);
+    DEBUG(errs()
+          << "LLVMSetLinkage(): LLVMDLLImportLinkage is no longer supported.");
     break;
   case LLVMDLLExportLinkage:
-    GV->setLinkage(GlobalValue::DLLExportLinkage);
+    DEBUG(errs()
+          << "LLVMSetLinkage(): LLVMDLLExportLinkage is no longer supported.");
     break;
   case LLVMExternalWeakLinkage:
     GV->setLinkage(GlobalValue::ExternalWeakLinkage);
diff --git a/lib/IR/Verifier.cpp b/lib/IR/Verifier.cpp
index 9e150e8575..d8e5c89598 100644
--- a/lib/IR/Verifier.cpp
+++ b/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...