Mangling: Add a mangling for back deployment fallback functions and update the back deployment thunk mangling to use the same prefix.

Author: tshortli

docs/ABI/Mangling.rst

@@ -223,7 +223,8 @@ types where the metadata itself has unknown layout.)
   global ::= global 'TI'                 // implementation of a dynamic_replaceable function
   global ::= global 'Tu'                 // async function pointer of a function
   global ::= global 'TX'                 // function pointer of a dynamic_replaceable function
-  global ::= global 'Tw'                 // back deployment thunk
+  global ::= global 'Twb'                // back deployment thunk
+  global ::= global 'TwB'                // back deployment fallback function
   global ::= entity entity 'TV'          // vtable override thunk, derived followed by base
   global ::= type label-list? 'D'        // type mangling for the debugger with label list for function types.
   global ::= type 'TC'                   // continuation prototype (not actually used for real symbols)

include/swift/AST/ASTMangler.h

@@ -106,7 +106,8 @@ class ASTMangler : public Mangler {
     DistributedThunk,
     DistributedAccessor,
     AccessibleFunctionRecord,
-    BackDeployedThunk,
+    BackDeploymentThunk,
+    BackDeploymentFallback,
   };
 
   ASTMangler(bool DWARFMangling = false)

include/swift/Demangling/DemangleNodes.def

@@ -332,7 +332,8 @@ NODE(CompileTimeConst)
 
 // Added in Swift 5.7
 NODE(OpaqueReturnTypeIndexed)
-NODE(BackDeployed)
+NODE(BackDeploymentThunk)
+NODE(BackDeploymentFallback)
 
 #undef CONTEXT_NODE
 #undef NODE

lib/AST/ASTMangler.cpp

@@ -857,9 +857,8 @@ void ASTMangler::appendSymbolKind(SymbolKind SKind) {
     case SymbolKind::DistributedThunk: return appendOperator("TE");
     case SymbolKind::DistributedAccessor: return appendOperator("TF");
     case SymbolKind::AccessibleFunctionRecord: return appendOperator("HF");
-    // FIXME(backDeploy): Check whether mangling needs to be extended since
-    // the available thunk mangling names are almost exhausted.
-    case SymbolKind::BackDeployedThunk: return appendOperator("Tw");
+    case SymbolKind::BackDeploymentThunk: return appendOperator("Twb");
+    case SymbolKind::BackDeploymentFallback: return appendOperator("TwB");
   }
 }
 

lib/Demangling/Demangler.cpp

@@ -139,6 +139,8 @@ bool swift::Demangle::isFunctionAttr(Node::Kind kind) {
     case Node::Kind::AsyncAwaitResumePartialFunction:
     case Node::Kind::AsyncSuspendResumePartialFunction:
     case Node::Kind::AccessibleFunctionRecord:
+    case Node::Kind::BackDeploymentThunk:
+    case Node::Kind::BackDeploymentFallback:
       return true;
     default:
       return false;
@@ -2395,7 +2397,6 @@ NodePointer Demangler::demangleThunkOrSpecialization() {
     case 'X': return createNode(Node::Kind::DynamicallyReplaceableFunctionVar);
     case 'x': return createNode(Node::Kind::DynamicallyReplaceableFunctionKey);
     case 'I': return createNode(Node::Kind::DynamicallyReplaceableFunctionImpl);
-    case 'w': return createNode(Node::Kind::BackDeployed);
     case 'Y':
     case 'Q': {
       NodePointer discriminator = demangleIndexAsNode();
@@ -2642,6 +2643,13 @@ NodePointer Demangler::demangleThunkOrSpecialization() {
         return demangleAutoDiffFunctionOrSimpleThunk(
             Node::Kind::AutoDiffFunction);
       }
+    case 'w':
+      switch (nextChar()) {
+      case 'b': return createNode(Node::Kind::BackDeploymentThunk);
+      case 'B': return createNode(Node::Kind::BackDeploymentFallback);
+      default:
+        return nullptr;
+      }
     default:
       return nullptr;
   }

lib/Demangling/NodePrinter.cpp

@@ -591,7 +591,8 @@ class NodePrinter {
     case Node::Kind::AsyncAwaitResumePartialFunction:
     case Node::Kind::AsyncSuspendResumePartialFunction:
     case Node::Kind::AccessibleFunctionRecord:
-    case Node::Kind::BackDeployed:
+    case Node::Kind::BackDeploymentThunk:
+    case Node::Kind::BackDeploymentFallback:
       return false;
     }
     printer_unreachable("bad node kind");
@@ -2051,11 +2052,14 @@ NodePointer NodePrinter::print(NodePointer Node, unsigned depth,
       Printer << "dynamically replaceable variable for ";
     }
     return nullptr;
-  case Node::Kind::BackDeployed:
+  case Node::Kind::BackDeploymentThunk:
     if (!Options.ShortenThunk) {
       Printer << "back deployment thunk for ";
     }
     return nullptr;
+  case Node::Kind::BackDeploymentFallback:
+    Printer << "back deployment fallback for ";
+    return nullptr;
   case Node::Kind::ProtocolSymbolicReference:
     Printer << "protocol symbolic reference 0x";
     Printer.writeHex(Node->getIndex());

lib/Demangling/OldRemangler.cpp

@@ -2801,7 +2801,13 @@ ManglingError Remangler::mangleAccessibleFunctionRecord(Node *node,
   return ManglingError::Success;
 }
 
-ManglingError Remangler::mangleBackDeployed(Node *node, unsigned depth) {
-  Buffer << "Tw";
+ManglingError Remangler::mangleBackDeploymentThunk(Node *node, unsigned depth) {
+  Buffer << "Twb";
+  return ManglingError::Success;
+}
+
+ManglingError Remangler::mangleBackDeploymentFallback(Node *node,
+                                                      unsigned depth) {
+  Buffer << "TwB";
   return ManglingError::Success;
 }

lib/Demangling/Remangler.cpp

@@ -1627,6 +1627,8 @@ ManglingError Remangler::mangleGlobal(Node *node, unsigned depth) {
       case Node::Kind::AsyncAwaitResumePartialFunction:
       case Node::Kind::AsyncSuspendResumePartialFunction:
       case Node::Kind::AccessibleFunctionRecord:
+      case Node::Kind::BackDeploymentThunk:
+      case Node::Kind::BackDeploymentFallback:
         mangleInReverseOrder = true;
         break;
       default:
@@ -3407,8 +3409,15 @@ ManglingError Remangler::mangleAccessibleFunctionRecord(Node *node,
   return ManglingError::Success;
 }
 
-ManglingError Remangler::mangleBackDeployed(Node *node, unsigned depth) {
-  Buffer << "Tw";
+ManglingError Remangler::mangleBackDeploymentThunk(Node *node,
+                                                   unsigned depth) {
+  Buffer << "Twb";
+  return ManglingError::Success;
+}
+
+ManglingError Remangler::mangleBackDeploymentFallback(Node *node,
+                                                      unsigned depth) {
+  Buffer << "TwB";
   return ManglingError::Success;
 }
 

test/Demangle/Inputs/manglings.txt

@@ -425,4 +425,5 @@ $s16distributed_test1XC7computeyS2iFTF ---> distributed accessor for distributed
 $s27distributed_actor_accessors7MyActorC7simple2ySSSiFTETFHF ---> accessible function runtime record for distributed accessor for distributed thunk for distributed_actor_accessors.MyActor.simple2(Swift.Int) -> Swift.String
 $s1A3bar1aySSYt_tF ---> A.bar(a: _const Swift.String) -> ()
 $s1t1fyyFSiAA3StrVcs7KeyPathCyADSiGcfu_SiADcfu0_33_556644b740b1b333fecb81e55a7cce98ADSiTf3npk_n ---> function signature specialization <Arg[1] = [Constant Propagated KeyPath : _556644b740b1b333fecb81e55a7cce98<t.Str,Swift.Int>]> of implicit closure #2 (t.Str) -> Swift.Int in implicit closure #1 (Swift.KeyPath<t.Str, Swift.Int>) -> (t.Str) -> Swift.Int in t.f() -> ()
-
+$s21back_deploy_attribute0A12DeployedFuncyyFTwb ---> back deployment thunk for back_deploy_attribute.backDeployedFunc() -> ()
+$s21back_deploy_attribute0A12DeployedFuncyyFTwB ---> back deployment fallback for back_deploy_attribute.backDeployedFunc() -> ()