cross-module-optimization: be more conservative when emitting a TBD file.

include/swift/AST/SILOptions.h

@@ -172,6 +172,8 @@ class SILOptions {
   /// Emit a mapping of profile counters for use in coverage.
   bool EmitProfileCoverageMapping = false;
 
+  bool emitTBD = false;
+
   /// Should we use a pass pipeline passed in via a json file? Null by default.
   llvm::StringRef ExternalPassPipelineFilename;
 

lib/Frontend/CompilerInvocation.cpp

@@ -1670,6 +1670,8 @@ static bool ParseSILArgs(SILOptions &Opts, ArgList &Args,
       OPT_disable_previous_implementation_calls_in_dynamic_replacements);
   Opts.ParseStdlib = FEOpts.ParseStdlib;
 
+  Opts.emitTBD = FEOpts.InputsAndOutputs.hasTBDPath();
+
   if (const Arg *A = Args.getLastArg(OPT_save_optimization_record_EQ)) {
     llvm::Expected<llvm::remarks::Format> formatOrErr =
         llvm::remarks::parseFormat(A->getValue());

lib/SILOptimizer/IPO/CrossModuleOptimization.cpp

@@ -338,12 +338,40 @@ bool CrossModuleOptimization::canSerializeType(SILType type) {
   return success;
 }
 
+/// Returns true if the function in \p funcCtxt could be linked statically to
+/// this module.
+static bool couldBeLinkedStatically(DeclContext *funcCtxt, SILModule &module) {
+  if (!funcCtxt)
+    return true;
+  ModuleDecl *funcModule = funcCtxt->getParentModule();
+  // If the function is in the same module, it's not in another module which
+  // could be linked statically.
+  if (module.getSwiftModule() == funcModule)
+    return false;
+
+  // The stdlib module is always linked dynamically.
+  if (funcModule == module.getASTContext().getStdlibModule())
+    return false;
+
+  // Conservatively assume the function is in a statically linked module.
+  return true;
+}
+
 /// Returns true if the function \p func can be used from a serialized function.
 bool CrossModuleOptimization::canUseFromInline(SILFunction *function) {
-  if (DeclContext *funcCtxt = function->getDeclContext()) {
-    if (!M.getSwiftModule()->canBeUsedForCrossModuleOptimization(funcCtxt))
-      return false;
-  }
+  DeclContext *funcCtxt = function->getDeclContext();
+  if (funcCtxt && !M.getSwiftModule()->canBeUsedForCrossModuleOptimization(funcCtxt))
+    return false;
+
+  /// If we are emitting a TBD file, the TBD file only contains public symbols
+  /// of this module. But not public symbols of imported modules which are
+  /// statically linked to the current binary.
+  /// This prevents referencing public symbols from other modules which could
+  /// (potentially) linked statically. Unfortunately there is no way to find out
+  /// if another module is linked statically or dynamically, so we have to be
+  /// conservative here.
+  if (conservative && M.getOptions().emitTBD && couldBeLinkedStatically(funcCtxt, M))
+    return false;
 
   switch (function->getLinkage()) {
   case SILLinkage::PublicNonABI:

test/SILOptimizer/Inputs/cross-module/default-module.swift

@@ -0,0 +1,10 @@
+
+import Submodule
+
+public func incrementByThree(_ x: Int) -> Int {
+  return incrementByOne(x) + 2
+}
+
+public func incrementByThreeWithCall(_ x: Int) -> Int {
+  return incrementByOneNoCMO(x) + 2
+}

test/SILOptimizer/Inputs/cross-module/default-submodule.swift

@@ -0,0 +1,10 @@
+
+public func incrementByOne(_ x: Int) -> Int {
+  return x + 1
+}
+
+@_semantics("optimize.no.crossmodule")
+public func incrementByOneNoCMO(_ x: Int) -> Int {
+  return x + 1
+}
+

test/SILOptimizer/default-cmo.swift

@@ -0,0 +1,43 @@
+
+// RUN: %empty-directory(%t) 
+
+// RUN: %target-build-swift -O -wmo -parse-as-library -emit-module -emit-module-path=%t/Submodule.swiftmodule -module-name=Submodule %S/Inputs/cross-module/default-submodule.swift -c -o %t/submodule.o
+// RUN: %target-build-swift -O -wmo -parse-as-library -emit-module -emit-module-path=%t/Module.swiftmodule -module-name=Module -I%t -I%S/Inputs/cross-module %S/Inputs/cross-module/default-module.swift -c -o %t/module.o
+// RUN: %target-build-swift -O -wmo -parse-as-library -emit-tbd -emit-tbd-path %t/ModuleTBD.tbd -emit-module -emit-module-path=%t/ModuleTBD.swiftmodule -module-name=ModuleTBD -I%t -I%S/Inputs/cross-module %S/Inputs/cross-module/default-module.swift -c -o %t/moduletbd.o
+
+// RUN: %target-build-swift -O -wmo -module-name=Main -I%t %s -emit-sil | %FileCheck %s
+
+
+import Module
+import ModuleTBD
+
+// CHECK-LABEL: sil @$s4Main11doIncrementyS2iF
+// CHECK-NOT:     function_ref 
+// CHECK-NOT:     apply 
+// CHECK:       } // end sil function '$s4Main11doIncrementyS2iF'
+public func doIncrement(_ x: Int) -> Int {
+  return Module.incrementByThree(x)
+}
+
+// CHECK-LABEL: sil @$s4Main19doIncrementWithCallyS2iF
+// CHECK:         function_ref @$s9Submodule19incrementByOneNoCMOyS2iF
+// CHECK:       } // end sil function '$s4Main19doIncrementWithCallyS2iF'
+public func doIncrementWithCall(_ x: Int) -> Int {
+  return Module.incrementByThreeWithCall(x)
+}
+
+// CHECK-LABEL: sil @$s4Main14doIncrementTBDyS2iF
+// CHECK-NOT:     function_ref 
+// CHECK-NOT:     apply 
+// CHECK:       } // end sil function '$s4Main14doIncrementTBDyS2iF'
+public func doIncrementTBD(_ x: Int) -> Int {
+  return ModuleTBD.incrementByThree(x)
+}
+
+// CHECK-LABEL: sil @$s4Main22doIncrementTBDWithCallyS2iF
+// CHECK:         function_ref @$s9ModuleTBD24incrementByThreeWithCallyS2iF
+// CHECK:       } // end sil function '$s4Main22doIncrementTBDWithCallyS2iF'
+public func doIncrementTBDWithCall(_ x: Int) -> Int {
+  return ModuleTBD.incrementByThreeWithCall(x)
+}
+