[embedded] Avoid changing lookupStdlibFunction, load findStringSwitchCaseWithCache in MPO instead

Author: kubamracek

SwiftCompilerSources/Sources/Optimizer/ModulePasses/MandatoryPerformanceOptimizations.swift

@@ -86,7 +86,8 @@ private func optimize(function: Function, _ context: FunctionPassContext, _ modu
   // 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") {
+        let f = context.lookupStdlibFunction(name: "_findStringSwitchCaseWithCache"),
+        context.loadFunction(function: f, loadCalleesRecursively: true) {
       worklist.pushIfNotVisited(f)
     }
   }

lib/SILOptimizer/PassManager/PassManager.cpp

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

stdlib/public/core/StringSwitch.swift

@@ -62,6 +62,7 @@ internal struct _StringSwitchContext {
 /// The \p cases array must not change between subsequent calls with the
 /// same \p cache.
 @_semantics("findStringSwitchCaseWithCache")
+@_used
 public // COMPILER_INTRINSIC
 func _findStringSwitchCaseWithCache(
   cases: [StaticString],