Update isAssignedOnlyOnceInInitializer to be more correct

Author: zoecarver

lib/SILOptimizer/IPO/GlobalOpt.cpp

@@ -104,6 +104,9 @@ class SILGlobalOpt {
   bool run();
 
 protected:
+  /// Checks if a given global variable is assigned only once.
+  bool isAssignedOnlyOnceInInitializer(SILGlobalVariable *SILG);
+
   /// If this is a call to a global initializer, map it.
   void collectGlobalInitCall(ApplyInst *AI);
 
@@ -595,15 +598,18 @@ static SILFunction *genGetterFromInit(SILOptFunctionBuilder &FunctionBuilder,
   return GetterF;
 }
 
-/// Checks if a given global variable is assigned only once.
-static bool isAssignedOnlyOnceInInitializer(SILGlobalVariable *SILG) {
+bool SILGlobalOpt::isAssignedOnlyOnceInInitializer(SILGlobalVariable *SILG) {
   if (SILG->isLet())
     return true;
-  // TODO: If we can prove that a given global variable
-  // is assigned only once, during initialization, then
-  // we can treat it as if it is a let.
-  // If this global is internal or private, it should be
-  return false;
+
+  // If we should skip this, it is probably because there are multiple stores.
+  // Return false if there are multiple stores or no stores.
+  if (GlobalVarSkipProcessing.count(SILG) || !GlobalVarStore.count(SILG))
+    return false;
+
+  // Otherwise, return true if this can't be used externally (false, otherwise).
+  return !isPossiblyUsedExternally(SILG->getLinkage(),
+                                   SILG->getModule().isWholeModule());
 }
 
 /// Replace load sequence which may contain

test/SILOptimizer/globalopt_global_propagation.swift

@@ -227,3 +227,25 @@ let IT2 = (100, 200, 300)
 public func test_let_tuple_wrapped_ints() -> Int {
   return IT1.0.0 + IT2.1
 }
+
+class Foo {
+  fileprivate static var x: Int = 0
+}
+
+// CHECK-LABEL: sil @$s28globalopt_global_propagation25test_optimize_init_staticSiyF
+// CHECK: bb0:
+// CHECK-NOT: global_addr
+// CHECK-NEXT: integer_literal
+// CHECK-NEXT: struct
+// CHECK-NEXT: return
+
+// CHECK-WMO-LABEL: sil @$s28globalopt_global_propagation25test_optimize_init_staticSiyF
+// CHECK-WMO: bb0:
+// CHECK-WMO-NOT: global_addr
+// CHECK-WMO-NEXT: integer_literal
+// CHECK-WMO-NEXT: struct
+// CHECK-WMO-NEXT: return
+public func test_optimize_init_static() -> Int {
+  return Foo.x
+}
+