Merge pull request #65557 from tshortli/unavailable-decl-optimization-stub

Introduce `stub` mode for `-unavailable-decl-optimization`

Author: tshortli

docs/ABI/Mangling.rst

@@ -301,6 +301,8 @@ are always non-polymorphic ``<impl-function-type>`` types.
   VALUE-WITNESS-KIND ::= 'ug'           // getEnumTag
   VALUE-WITNESS-KIND ::= 'up'           // destructiveProjectEnumData
   VALUE-WITNESS-KIND ::= 'ui'           // destructiveInjectEnumTag
+  VALUE-WITNESS-KIND ::= 'et'           // getEnumTagSinglePayload
+  VALUE-WITNESS-KIND ::= 'st'           // storeEnumTagSinglePayload
 
 ``<VALUE-WITNESS-KIND>`` differentiates the kinds of value
 witness functions for a type.

include/swift/AST/KnownDecls.def

@@ -68,6 +68,7 @@ FUNC_DECL(DiagnoseUnexpectedError, "_unexpectedError")
 FUNC_DECL(DiagnoseUnexpectedNilOptional, "_diagnoseUnexpectedNilOptional")
 FUNC_DECL(DiagnoseUnexpectedEnumCase, "_diagnoseUnexpectedEnumCase")
 FUNC_DECL(DiagnoseUnexpectedEnumCaseValue, "_diagnoseUnexpectedEnumCaseValue")
+FUNC_DECL(DiagnoseUnavailableCodeReached, "_diagnoseUnavailableCodeReached")
 
 FUNC_DECL(GetErrorEmbeddedNSError, "_getErrorEmbeddedNSError")
 

include/swift/Basic/LangOptions.h

@@ -112,6 +112,12 @@ namespace swift {
     /// resulting binary by default in this mode.
     None,
 
+    /// Stub out code associated with unavailable declarations.
+    ///
+    /// For example, the bodies of unavailable functions should be compiled as
+    /// if they just contained a call to fatalError().
+    Stub,
+
     /// Avoid generating any code for unavailable declarations.
     ///
     /// NOTE: This optimization can be ABI breaking for a library evolution

include/swift/SIL/ApplySite.h

@@ -241,6 +241,12 @@ class ApplySite {
     FOREACH_IMPL_RETURN(isCalleeKnownProgramTerminationPoint());
   }
 
+  /// Returns true if the callee function is annotated with
+  /// @_semantics("unavailable_code_reached")
+  bool isCalleeUnavailableCodeReached() const {
+    FOREACH_IMPL_RETURN(isCalleeUnavailableCodeReached());
+  }
+
   /// Check if this is a call of a never-returning function.
   bool isCalleeNoReturn() const { FOREACH_IMPL_RETURN(isCalleeNoReturn()); }
 

include/swift/SIL/SILInstruction.h

@@ -2777,6 +2777,14 @@ class ApplyInstBase<Impl, Base, false> : public Base {
     return calleeFn->hasSemanticsAttr(SEMANTICS_PROGRAMTERMINATION_POINT);
   }
 
+  /// Returns true if the callee function is annotated with
+  /// @_semantics("unavailable_code_reached")
+  bool isCalleeUnavailableCodeReached() const {
+    auto calleeFn = getCalleeFunction();
+    if (!calleeFn) return false;
+    return calleeFn->hasSemanticsAttr(SEMANTICS_UNAVAILABLE_CODE_REACHED);
+  }
+
   /// True if this application has generic substitutions.
   bool hasSubstitutions() const {
     return Substitutions.hasAnySubstitutableParams();

include/swift/SIL/SILModule.h

@@ -1087,6 +1087,10 @@ LLVM_LIBRARY_VISIBILITY bool usesObjCAllocator(ClassDecl *theClass);
 /// A declaration may not require lowering if, for example, it is annotated as
 /// unavailable and optimization settings allow it to be omitted.
 LLVM_LIBRARY_VISIBILITY bool shouldSkipLowering(Decl *D);
+
+/// Returns true if SIL/IR lowering for the given declaration should produce
+/// a stub that traps at runtime because the code ought to be unreachable.
+LLVM_LIBRARY_VISIBILITY bool shouldLowerToUnavailableCodeStub(Decl *D);
 } // namespace Lowering
 
 /// Apply the given function to each ABI member of \c D skipping the members

include/swift/Strings.h

@@ -60,6 +60,9 @@ constexpr static const StringLiteral SEMANTICS_PROGRAMTERMINATION_POINT =
 constexpr static const StringLiteral SEMANTICS_DEFAULT_ACTOR =
     "defaultActor";
 
+constexpr static const StringLiteral SEMANTICS_UNAVAILABLE_CODE_REACHED =
+    "unavailable_code_reached";
+
 constexpr static const StringLiteral DEFAULT_ACTOR_STORAGE_FIELD_NAME =
     "$defaultActor";
 

lib/ClangImporter/ClangImporter.cpp

@@ -6560,7 +6560,6 @@ CxxRecordSemanticsKind
 CxxRecordSemantics::evaluate(Evaluator &evaluator,
                              CxxRecordSemanticsDescriptor desc) const {
   const auto *decl = desc.decl;
-  auto &clangSema = desc.ctx.getClangModuleLoader()->getClangSema();
 
   if (hasImportAsRefAttr(decl)) {
     return CxxRecordSemanticsKind::Reference;

lib/Frontend/CompilerInvocation.cpp

@@ -614,6 +614,7 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
     auto value =
         llvm::StringSwitch<Optional<UnavailableDeclOptimization>>(A->getValue())
             .Case("none", UnavailableDeclOptimization::None)
+            .Case("stub", UnavailableDeclOptimization::Stub)
             .Case("complete", UnavailableDeclOptimization::Complete)
             .Default(None);
 

lib/SIL/IR/SILModule.cpp

@@ -965,3 +965,13 @@ bool Lowering::shouldSkipLowering(Decl *D) {
   // -unavailable-decl-optimization=complete is specified.
   return D->getSemanticUnavailableAttr() != None;
 }
+
+bool Lowering::shouldLowerToUnavailableCodeStub(Decl *D) {
+  if (D->getASTContext().LangOpts.UnavailableDeclOptimizationMode !=
+      UnavailableDeclOptimization::Stub)
+    return false;
+
+  // Unavailable declarations should trap at runtime if
+  // -unavailable-decl-optimization=stub is specified.
+  return D->getSemanticUnavailableAttr() != None;
+}