Preserve extern_weak linkage in CloneModule.

[eugenis]

Summary

Only force "extern" linkage if the function used to be a definition
in the source module. Declarations keep their original linkage.

[pcc]

lib/Transforms/Utils/CloneModule.cpp

128–129

Shouldn't we also do this for global variables?

[pcc]

LGTM with a test for global variables

[eugenis]

In D18536#388632, @pcc wrote:

LGTM with a test for global variables

done

[eugenis]

r265043

lib/Transforms/Utils/CloneModule.cpp

std::unique_ptr<Module> llvm::CloneModule(
   }
   
   // Now that all of the things that global variable initializer can refer to
   // have been created, loop through and copy the global variable referrers
   // over...  We also set the attributes on the global now.
   //
   for (Module::const_global_iterator I = M->global_begin(), E = M->global_end();
        I != E; ++I) {
+    if (I->isDeclaration())
+      continue;
+
     GlobalVariable *GV = cast<GlobalVariable>(VMap[&*I]);
     if (!ShouldCloneDefinition(&*I)) {
       // Skip after setting the correct linkage for an external reference.
       GV->setLinkage(GlobalValue::ExternalLinkage);
       continue;
     }
     if (I->hasInitializer())
       GV->setInitializer(MapValue(I->getInitializer(), VMap));
   }
 
   // Similarly, copy over function bodies now...
   //
   for (Module::const_iterator I = M->begin(), E = M->end(); I != E; ++I) {
+    if (I->isDeclaration())
+      continue;
+
     Function *F = cast<Function>(VMap[&*I]);
     if (!ShouldCloneDefinition(&*I)) {
       // Skip after setting the correct linkage for an external reference.
       F->setLinkage(GlobalValue::ExternalLinkage);
       // Personality function is not valid on a declaration.
       F->setPersonalityFn(nullptr);
       continue;
     }
-    if (!I->isDeclaration()) {
-      Function::arg_iterator DestI = F->arg_begin();
-      for (Function::const_arg_iterator J = I->arg_begin(); J != I->arg_end();
-           ++J) {
-        DestI->setName(J->getName());
-        VMap[&*J] = &*DestI++;
-      }
+
 
-      SmallVector<ReturnInst*, 8> Returns;  // Ignore returns cloned.
-      CloneFunctionInto(F, &*I, VMap, /*ModuleLevelChanges=*/true, Returns);
-    }
+    SmallVector<ReturnInst *, 8> Returns; // Ignore returns cloned.
 
     if (I->hasPersonalityFn())
       F->setPersonalityFn(MapValue(I->getPersonalityFn(), VMap));
   }
 
   // And aliases
   for (Module::const_alias_iterator I = M->alias_begin(), E = M->alias_end();
        I != E; ++I) {

test/tools/llvm-split/extern_linkage.ll

+; Test that extern_weak linkage is preserved.
+; RUN: llvm-split -o %t %s
+; RUN: llvm-dis -o - %t0 | FileCheck %s
+; RUN: llvm-dis -o - %t1 | FileCheck %s
+
+; Both declarations are extern_weak declaration in all partitions.
+
+; CHECK: @x = extern_weak global i32, align 4
+@x = extern_weak global i32, align 4
+
+; CHECK: declare extern_weak void @f(...)
+declare extern_weak void @f(...)