[embedded] Support _findStringSwitchCaseWithCache in Embedded Swift

Author: kubamracek

SwiftCompilerSources/Sources/Optimizer/ModulePasses/MandatoryPerformanceOptimizations.swift

@@ -80,6 +80,16 @@ fileprivate struct PathFunctionTuple: Hashable {
 
 private func optimize(function: Function, _ context: FunctionPassContext, _ moduleContext: ModulePassContext, _ worklist: inout FunctionWorklist) {
   var alreadyInlinedFunctions: Set<PathFunctionTuple> = Set()
+
+  // ObjectOutliner replaces calls to findStringSwitchCase with _findStringSwitchCaseWithCache, but this happens as a late SIL optimization,
+  // which is a problem for Embedded Swift, because _findStringSwitchCaseWithCache will then reference non-specialized code. Solve this by
+  // eagerly linking and specializing _findStringSwitchCaseWithCache whenever findStringSwitchCase is found in the module.
+  if context.options.enableEmbeddedSwift {
+    if function.hasSemanticsAttribute("findStringSwitchCase"),
+        let f = context.lookupStdlibFunction(name: "_findStringSwitchCaseWithCache") {
+      worklist.pushIfNotVisited(f)
+    }
+  }
 
   var changed = true
   while changed {

lib/SILOptimizer/PassManager/PassManager.cpp

@@ -1929,7 +1929,11 @@ OptionalBridgedFunction BridgedPassContext::lookupStdlibFunction(BridgedStringRe
 
   SILDeclRef declRef(decl, SILDeclRef::Kind::Func);
   SILOptFunctionBuilder funcBuilder(*invocation->getTransform());
-  return {funcBuilder.getOrCreateFunction(SILLocation(decl), declRef, NotForDefinition)};
+  SILFunction *function = funcBuilder.getOrCreateFunction(SILLocation(decl), declRef, NotForDefinition);
+  if (mod->getOptions().EmbeddedSwift) {
+    mod->linkFunction(function, SILModule::LinkingMode::LinkAll);
+  }
+  return {function};
 }
 
 OptionalBridgedFunction BridgedPassContext::lookUpNominalDeinitFunction(BridgedDeclObj nominal)  const {

test/embedded/string-switch2.swift

@@ -0,0 +1,37 @@
+// RUN: %target-run-simple-swift(-enable-experimental-feature Embedded -wmo -O -Xlinker %swift_obj_root/lib/swift/embedded/%target-cpu-apple-macos/libswiftUnicodeDataTables.a) | %FileCheck %s
+
+// REQUIRES: swift_in_compiler
+// REQUIRES: executable_test
+// REQUIRES: optimized_stdlib
+// REQUIRES: swift_stdlib_no_asserts
+// REQUIRES: OS=macosx
+// REQUIRES: swift_feature_Embedded
+
+enum MyEnum: String {
+    case case1
+    case case2
+    case case3
+    case case4
+    case case5
+    case case6
+    case case7
+    case case8
+    case case9
+    case case10
+    case case11
+    case case12
+    case case13
+    case case14
+    case case15
+    case case16
+    case case17
+    case case18
+    case case19
+}
+
+var e = MyEnum.case1
+print(e.rawValue)
+e = MyEnum.case2
+print(e.rawValue)
+// CHECK: case1
+// CHECK: case2