rework cross-module-optimization

* rename the CrossModuleSerializationSetup pass to simply CrossModuleOptimization
* remove the CMO specific serializer pass. Instead run the CrossModuleSerializationSetup pass directly before the standard serializer pass.
* correctly handle shared functions (e.g. specializations)
* refactoring

Author: eeckstein

include/swift/SILOptimizer/PassManager/Passes.def

@@ -110,8 +110,8 @@ PASS(AccessEnforcementSelection, "access-enforcement-selection",
      "Access Enforcement Selection")
 PASS(AccessEnforcementWMO, "access-enforcement-wmo",
      "Access Enforcement Whole Module Optimization")
-PASS(CrossModuleSerializationSetup, "cross-module-serialization-setup",
-     "Setup serialization flags for cross-module optimization")
+PASS(CrossModuleOptimization, "cmo",
+     "Perform cross-module optimization")
 PASS(AccessSummaryDumper, "access-summary-dump",
      "Dump Address Parameter Access Summary")
 PASS(AccessStorageAnalysisDumper, "access-storage-analysis-dump",
@@ -405,8 +405,6 @@ PASS(SimplifyUnreachableContainingBlocks, "simplify-unreachable-containing-block
      "Utility pass. Removes all non-term insts from blocks with unreachable terms")
 PASS(SerializeSILPass, "serialize-sil",
      "Utility pass. Serializes the current SILModule")
-PASS(CMOSerializeSILPass, "cmo-serialize-sil",
-     "Utility pass. Serializes the current SILModule for cross-module-optimization")
 PASS(YieldOnceCheck, "yield-once-check",
     "Check correct usage of yields in yield-once coroutines")
 PASS(OSLogOptimization, "os-log-optimization", "Optimize os log calls")

lib/AST/Module.cpp

@@ -2374,17 +2374,18 @@ canBeUsedForCrossModuleOptimization(DeclContext *ctxt) const {
   // See if context is imported in a "regular" way, i.e. not with
   // @_implementationOnly or @_spi.
   ModuleDecl::ImportFilter filter = {
-    ModuleDecl::ImportFilterKind::Exported,
-    ModuleDecl::ImportFilterKind::Default};
+    ModuleDecl::ImportFilterKind::ImplementationOnly,
+    ModuleDecl::ImportFilterKind::SPIAccessControl
+  };
   SmallVector<ImportedModule, 4> results;
   getImportedModules(results, filter);
 
   auto &imports = getASTContext().getImportCache();
   for (auto &desc : results) {
     if (imports.isImportedBy(moduleOfCtxt, desc.importedModule))
-      return true;
+      return false;
   }
-  return false;
+  return true;
 }
 
 void SourceFile::lookupImportedSPIGroups(

lib/SILOptimizer/IPO/CMakeLists.txt

@@ -1,7 +1,7 @@
 target_sources(swiftSILOptimizer PRIVATE
   CapturePropagation.cpp
   ClosureSpecializer.cpp
-  CrossModuleSerializationSetup.cpp
+  CrossModuleOptimization.cpp
   DeadFunctionElimination.cpp
   GlobalOpt.cpp
   GlobalPropertyOpt.cpp