cross-module-optimization: fix a problem with global variables

don't make public external globals non-external

Author: eeckstein

lib/SILOptimizer/IPO/CrossModuleOptimization.cpp

@@ -268,6 +268,12 @@ bool CrossModuleOptimization::canSerializeInstruction(SILInstruction *inst,
 
     return true;
   }
+  if (auto *GAI = dyn_cast<GlobalAddrInst>(inst)) {
+    SILGlobalVariable *global = GAI->getReferencedGlobal();
+    if (conservative && !hasPublicVisibility(global->getLinkage()))
+      return false;
+    return true;
+  }
   if (auto *KPI = dyn_cast<KeyPathInst>(inst)) {
     bool canUse = true;
     KPI->getPattern()->visitReferencedFunctionsAndMethods(
@@ -457,7 +463,7 @@ void CrossModuleOptimization::serializeInstruction(SILInstruction *inst,
     if (canSerializeGlobal(global)) {
       serializeGlobal(global);
     }
-    if (global->getLinkage() != SILLinkage::Public) {
+    if (!hasPublicVisibility(global->getLinkage())) {
       global->setLinkage(SILLinkage::Public);
       M.addPublicCMOSymbol(global->getName());
     }

test/SILOptimizer/Inputs/cross-module/cross-module.swift

@@ -290,3 +290,7 @@ public struct StructWithClosure {
   public static let c = { (x: Int) -> Int in return x }
 }
 
+public func getEmptySet() -> Set<Int> {
+  return Set()
+}
+

test/SILOptimizer/cross-module-optimization.swift

@@ -27,6 +27,7 @@
 
 import Test
 
+// CHECK-SIL: sil_global public_external [serialized] @_swiftEmptySetSingleton : $_SwiftEmptySetSingleton
 
 func testNestedTypes() {
   let c = Container()
@@ -132,6 +133,9 @@ func testMisc() {
 
   // CHECK-OUTPUT: 27
   print(classWithPublicProperty(33))
+
+  // CHECK-OUTPUT: []
+  print(getEmptySet())
 }
 
 // CHECK-SIL2-LABEL: sil hidden [noinline] @$s4Main10testGlobalyyF