IRgen support for weak_import.

- <rdar://problem/6652110> clang should support weak_import


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@66270 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/CodeGenModule.cpp

@@ -263,8 +263,12 @@ void CodeGenModule::SetGlobalValueAttributes(const Decl *D,
         } else
           GV->setLinkage(llvm::Function::DLLImportLinkage);
       }
-    } else if (D->getAttr<WeakAttr>())
+    } else if (D->getAttr<WeakAttr>() || 
+               D->getAttr<WeakImportAttr>()) {
+      // "extern_weak" is overloaded in LLVM; we probably should have
+      // separate linkage types for this. 
       GV->setLinkage(llvm::Function::ExternalWeakLinkage);
+   }
   } else {
     if (IsInternal) {
       GV->setLinkage(llvm::Function::InternalLinkage);
@@ -276,7 +280,8 @@ void CodeGenModule::SetGlobalValueAttributes(const Decl *D,
             GV->setLinkage(llvm::Function::DLLExportLinkage);
         } else
           GV->setLinkage(llvm::Function::DLLExportLinkage);
-      } else if (D->getAttr<WeakAttr>() || IsInline)
+      } else if (D->getAttr<WeakAttr>() || D->getAttr<WeakImportAttr>() || 
+                 IsInline)
         GV->setLinkage(llvm::Function::WeakLinkage);
     }
   }
@@ -602,7 +607,7 @@ void CodeGenModule::EmitGlobalDefinition(const ValueDecl *D) {
     if (D->getStorageClass() == VarDecl::PrivateExtern)
       setGlobalVisibility(GV, VisibilityAttr::HiddenVisibility);
 
-    if (D->getAttr<WeakAttr>())
+    if (D->getAttr<WeakAttr>() || D->getAttr<WeakImportAttr>())
       GV->setLinkage(llvm::GlobalValue::ExternalWeakLinkage);
 
     if (const AsmLabelAttr *ALA = D->getAttr<AsmLabelAttr>()) {
@@ -737,7 +742,7 @@ void CodeGenModule::EmitGlobalVarDefinition(const VarDecl *D) {
     GV->setLinkage(llvm::Function::DLLImportLinkage);
   else if (D->getAttr<DLLExportAttr>())
     GV->setLinkage(llvm::Function::DLLExportLinkage);
-  else if (D->getAttr<WeakAttr>())
+  else if (D->getAttr<WeakAttr>() || D->getAttr<WeakImportAttr>())
     GV->setLinkage(llvm::GlobalVariable::WeakLinkage);
   else {
     // FIXME: This isn't right.  This should handle common linkage and other

test/CodeGen/attributes.c

@@ -13,6 +13,8 @@
 // RUN: grep '@t12 =.*section "SECT"' %t &&
 // RUN: grep '@t13 =.*section "SECT"' %t &&
 // RUN: grep '@t14.x =.*section "SECT"' %t
+// RUN: grep 'declare extern_weak i32 @t15()' %t &&
+// RUN: grep '@t16 = extern_weak global i32' %t
 
 void t1() __attribute__((noreturn));
 void t1() {}
@@ -47,3 +49,11 @@ struct s0 t13 __attribute__((section("SECT"))) = { 0 };
 void t14(void) {
   static int x __attribute__((section("SECT"))) = 0;
 }
+
+int __attribute__((weak_import)) t15(void);
+extern int t16 __attribute__((weak_import));
+int t17() {
+  return t15() + t16;
+}
+
+