[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/IPO/DeadFunctionElimination.cpp

@@ -124,6 +124,14 @@ class DeadFunctionAndGlobalElimination {
     if (F->getRepresentation() == SILFunctionTypeRepresentation::ObjCMethod)
       return true;
 
+    // To support ObjectOutliner's replacing of calls to findStringSwitchCase
+    // with _findStringSwitchCaseWithCache. In Embedded Swift, we have to load
+    // the body of this function early and specialize it, so that ObjectOutliner
+    // can reference it later. To make this work we have to avoid DFE'ing it.
+    // Linker's dead-stripping will eventually remove this if actually unused.
+    if (F->hasSemanticsAttr("findStringSwitchCaseWithCache"))
+      return true;
+
     return false;
   }
 

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 {