[SILGen] Make it possible to emit generator function given its body and result type

This would be used for runtime attribute generators that have to
emit `if #available(...)` block in the body which is much easier
to do during Sema.

Author: xedin

lib/SILGen/SILGenFunction.cpp

@@ -1153,6 +1153,28 @@ void SILGenFunction::emitGeneratorFunction(SILDeclRef function, VarDecl *var) {
   emitEpilog(loc);
 }
 
+void SILGenFunction::emitGeneratorFunction(SILDeclRef function,
+                                           Type resultInterfaceType,
+                                           BraceStmt *body) {
+  MagicFunctionName = SILGenModule::getMagicFunctionName(function);
+
+  RegularLocation loc(body);
+  loc.markAutoGenerated();
+
+  auto *dc = function.getDecl()->getInnermostDeclContext();
+  auto captureInfo = SGM.M.Types.getLoweredLocalCaptures(function);
+  emitProlog(captureInfo, ParameterList::createEmpty(getASTContext()),
+             /*selfParam=*/nullptr, dc, resultInterfaceType, /*throws=*/false,
+             SourceLoc());
+
+  prepareEpilog(resultInterfaceType, /*hasThrows=*/false, CleanupLocation(loc));
+
+  emitStmt(body);
+
+  emitEpilog(loc);
+  mergeCleanupBlocks();
+}
+
 void SILGenFunction::emitProfilerIncrement(ASTNode Node) {
   emitProfilerIncrement(ProfileCounterRef::node(Node));
 }

lib/SILGen/SILGenFunction.h

@@ -756,6 +756,11 @@ class LLVM_LIBRARY_VISIBILITY SILGenFunction
   /// expression initializer.
   void emitGeneratorFunction(SILDeclRef function, VarDecl *var);
 
+  /// Generate a nullary function that has the given result interface type and
+  /// body.
+  void emitGeneratorFunction(SILDeclRef function, Type resultInterfaceType,
+                             BraceStmt *body);
+
   /// Generate an ObjC-compatible destructor (-dealloc).
   void emitObjCDestructor(SILDeclRef dtor);