Linker: Create a function declaration when moving a non-prevailing alias of function type.

[pcc]

Summary

We were previously creating a global variable of function type,
which is invalid IR. This issue was exposed by r304690, in which we
started asserting that global variables were of a valid type.

Fixes PR33462.

llvm/trunk/lib/Linker/IRMover.cpp

GlobalValue *IRLinker::copyGlobalValueProto(const GlobalValue *SGV,
   GlobalValue *NewGV;
   if (auto *SGVar = dyn_cast<GlobalVariable>(SGV)) {
     NewGV = copyGlobalVariableProto(SGVar);
   } else if (auto *SF = dyn_cast<Function>(SGV)) {
     NewGV = copyFunctionProto(SF);
   } else {
     if (ForDefinition)
       NewGV = copyGlobalAliasProto(cast<GlobalAlias>(SGV));
+    else if (SGV->getValueType()->isFunctionTy())
+      NewGV =
+          Function::Create(cast<FunctionType>(TypeMap.get(SGV->getValueType())),
+                           GlobalValue::ExternalLinkage, SGV->getName(), &DstM);
     else
       NewGV = new GlobalVariable(
           DstM, TypeMap.get(SGV->getValueType()),
           /*isConstant*/ false, GlobalValue::ExternalLinkage,
           /*init*/ nullptr, SGV->getName(),
           /*insertbefore*/ nullptr, SGV->getThreadLocalMode(),
           SGV->getType()->getAddressSpace());
   }

llvm/trunk/test/LTO/Resolution/X86/function-alias-non-prevailing.ll

+; RUN: llvm-as -o %t %s
+; RUN: llvm-lto2 run %t -r %t,foo, -r %t,baz,p -o %t2 -save-temps
+; RUN: llvm-dis -o - %t2.0.0.preopt.bc | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64--fuchsia"
+
+; CHECK: declare void @foo()
+@foo = weak alias void(), void()* @bar
+
+define internal void @bar() {
+  ret void
+}
+
+define void()* @baz() {
+  ret void()* @foo
+}