[thunk-lowering] Add a pass that performs lowering of ThunkInsts.

Right now it just handles the "identity" case so we can validate the
functionality.

Author: gottesmm

include/swift/SIL/SILModule.h

@@ -644,6 +644,13 @@ class SILModule {
     return {functions.begin(), functions.end()};
   }
 
+  /// Move \p fn to be in the function list before \p moveBefore.
+  void moveBefore(SILModule::iterator moveBefore, SILFunction *fn);
+
+  /// Move \p fn to be in the function list after \p moveAfter. It is assumed
+  /// that \p moveAfter is not end.
+  void moveAfter(SILModule::iterator moveAfter, SILFunction *fn);
+
   const_iterator zombies_begin() const { return zombieFunctions.begin(); }
   const_iterator zombies_end() const { return zombieFunctions.end(); }
 

include/swift/SILOptimizer/PassManager/Passes.def

@@ -510,6 +510,8 @@ SWIFT_FUNCTION_PASS(UpdateBorrowedFrom, "update-borrowed-from",
      "Test pass for update borrowed-from instructions")
 PASS(DiagnoseUnnecessaryPreconcurrencyImports, "sil-diagnose-unnecessary-preconcurrency-imports",
      "Diagnose any preconcurrency imports that Sema and TransferNonSendable did not use")
+PASS(ThunkLowering, "sil-thunk-lowering",
+     "Lower thunk instructions to actual thunks")
 PASS(PruneVTables, "prune-vtables",
      "Mark class methods that do not require vtable dispatch")
 PASS_RANGE(AllPasses, AliasInfoDumper, PruneVTables)

lib/SIL/IR/SILModule.cpp

@@ -940,6 +940,26 @@ void SILModule::performOnceForPrespecializedImportedExtensions(
   prespecializedFunctionDeclsImported = true;
 }
 
+void SILModule::moveBefore(SILModule::iterator moveAfter, SILFunction *fn) {
+  assert(&fn->getModule() == this);
+  assert(&moveAfter->getModule() == this);
+  assert(moveAfter != end() &&
+         "We assume that moveAfter must not be end since nothing is after end");
+
+  getFunctionList().remove(fn->getIterator());
+  getFunctionList().insert(moveAfter, fn);
+}
+
+void SILModule::moveAfter(SILModule::iterator moveAfter, SILFunction *fn) {
+  assert(&fn->getModule() == this);
+  assert(&moveAfter->getModule() == this);
+  assert(moveAfter != end() &&
+         "We assume that moveAfter must not be end since nothing is after end");
+
+  getFunctionList().remove(fn->getIterator());
+  getFunctionList().insertAfter(moveAfter, fn);
+}
+
 SILProperty *
 SILProperty::create(SILModule &M, unsigned Serialized, AbstractStorageDecl *Decl,
                     std::optional<KeyPathPatternComponent> Component) {

lib/SILOptimizer/Mandatory/CMakeLists.txt

@@ -44,6 +44,7 @@ target_sources(swiftSILOptimizer PRIVATE
   PMOMemoryUseCollector.cpp
   RawSILInstLowering.cpp
   ReferenceBindingTransform.cpp
+  ThunkLowering.cpp
   TransferNonSendable.cpp
   LowerTupleAddrConstructor.cpp
   SILGenCleanup.cpp