Merge pull request #79242 from kubamracek/embedded-mergeable-symbols

[embedded] Add an experimental -Xfrontend -mergeable-symbols to allow linking multiple .o modules in Embedded Swift

Author: kubamracek

include/swift/AST/IRGenOptions.h

@@ -461,6 +461,8 @@ class IRGenOptions {
   /// Internalize symbols (static library) - do not export any public symbols.
   unsigned InternalizeSymbols : 1;
 
+  unsigned MergeableSymbols : 1;
+
   /// Emit a section with references to class_ro_t* in generic class patterns.
   unsigned EmitGenericRODatas : 1;
 
@@ -590,6 +592,7 @@ class IRGenOptions {
         EnableGlobalISel(false), VirtualFunctionElimination(false),
         WitnessMethodElimination(false), ConditionalRuntimeRecords(false),
         InternalizeAtLink(false), InternalizeSymbols(false),
+        MergeableSymbols(false),
         EmitGenericRODatas(true), NoPreallocatedInstantiationCaches(false),
         DisableReadonlyStaticObjects(false), CollocatedMetadataFunctions(false),
         ColocateTypeDescriptors(true), UseRelativeProtocolWitnessTables(false),

include/swift/IRGen/Linking.h

@@ -56,10 +56,15 @@ class UniversalLinkageInfo {
   /// be promoted to public external. Used by the LLDB expression evaluator.
   bool ForcePublicDecls;
 
+  /// When true, allows duplicate external and hidden declarations by marking
+  /// them as linkonce / weak.
+  bool MergeableSymbols;
+
   explicit UniversalLinkageInfo(IRGenModule &IGM);
 
   UniversalLinkageInfo(const llvm::Triple &triple, bool hasMultipleIGMs,
-                       bool forcePublicDecls, bool isStaticLibrary);
+                       bool forcePublicDecls, bool isStaticLibrary,
+                       bool mergeableSymbols);
 
   /// In case of multiple llvm modules (in multi-threaded compilation) all
   /// private decls must be visible from other files.

include/swift/Option/FrontendOptions.td

@@ -766,6 +766,10 @@ def conditional_runtime_records : Flag<["-"], "conditional-runtime-records">,
   Flags<[FrontendOption, NoInteractiveOption, HelpHidden]>,
   HelpText<"Allow removal of runtime metadata records (public types, protocol conformances) based on whether they're used or unused">;
 
+def mergeable_symbols : Flag<["-"], "mergeable-symbols">,
+  Flags<[FrontendOption, NoInteractiveOption, HelpHidden]>,
+  HelpText<"Emit symbol definitions as mergeable (linkonce_odr)">;
+
 def disable_preallocated_instantiation_caches : Flag<["-"], "disable-preallocated-instantiation-caches">,
   Flags<[FrontendOption, NoInteractiveOption, HelpHidden]>,
   HelpText<"Avoid preallocating metadata instantiation caches in globals">;

lib/Frontend/CompilerInvocation.cpp

@@ -3553,6 +3553,10 @@ static bool ParseIRGenArgs(IRGenOptions &Opts, ArgList &Args,
 
   Opts.InternalizeSymbols = FrontendOpts.Static;
 
+  if (Args.hasArg(OPT_mergeable_symbols)) {
+    Opts.MergeableSymbols = true;
+  }
+
   if (Args.hasArg(OPT_disable_preallocated_instantiation_caches)) {
     Opts.NoPreallocatedInstantiationCaches = true;
   }

lib/IRGen/GenDecl.cpp

@@ -2249,10 +2249,16 @@ getIRLinkage(StringRef name, const UniversalLinkageInfo &info,
 
   switch (linkage) {
   case SILLinkage::Public:
-  case SILLinkage::Package:
-    return {llvm::GlobalValue::ExternalLinkage, PublicDefinitionVisibility,
+  case SILLinkage::Package: {
+    auto linkage = llvm::GlobalValue::ExternalLinkage;
+
+    if (info.MergeableSymbols)
+      linkage = llvm::GlobalValue::LinkOnceODRLinkage;
+
+    return {linkage, PublicDefinitionVisibility,
             info.Internalize ? llvm::GlobalValue::DefaultStorageClass
                              : ExportedStorage};
+  }
 
   case SILLinkage::PublicNonABI:
   case SILLinkage::PackageNonABI:
@@ -2264,6 +2270,9 @@ getIRLinkage(StringRef name, const UniversalLinkageInfo &info,
                         : RESULT(External, Hidden, Default);
 
   case SILLinkage::Hidden:
+    if (info.MergeableSymbols)
+      return RESULT(LinkOnceODR, Hidden, Default);
+
     return RESULT(External, Hidden, Default);
 
   case SILLinkage::Private: {

lib/IRGen/Linking.cpp

@@ -82,16 +82,19 @@ bool swift::irgen::useDllStorage(const llvm::Triple &triple) {
 UniversalLinkageInfo::UniversalLinkageInfo(IRGenModule &IGM)
     : UniversalLinkageInfo(IGM.Triple, IGM.IRGen.hasMultipleIGMs(),
                            IGM.IRGen.Opts.ForcePublicLinkage,
-                           IGM.IRGen.Opts.InternalizeSymbols) {}
+                           IGM.IRGen.Opts.InternalizeSymbols,
+                           IGM.IRGen.Opts.MergeableSymbols) {}
 
 UniversalLinkageInfo::UniversalLinkageInfo(const llvm::Triple &triple,
                                            bool hasMultipleIGMs,
                                            bool forcePublicDecls,
-                                           bool isStaticLibrary)
+                                           bool isStaticLibrary,
+                                           bool mergeableSymbols)
     : IsELFObject(triple.isOSBinFormatELF()),
       IsMSVCEnvironment(triple.isWindowsMSVCEnvironment()),
       UseDLLStorage(useDllStorage(triple)), Internalize(isStaticLibrary),
-      HasMultipleIGMs(hasMultipleIGMs), ForcePublicDecls(forcePublicDecls) {}
+      HasMultipleIGMs(hasMultipleIGMs), ForcePublicDecls(forcePublicDecls),
+      MergeableSymbols(mergeableSymbols) {}
 
 LinkEntity LinkEntity::forSILGlobalVariable(SILGlobalVariable *G,
                                             IRGenModule &IGM) {

lib/IRGen/TBDGenVisitor.h

@@ -126,7 +126,7 @@ class TBDGenVisitor : public IRSymbolVisitor {
                 APIRecorder &recorder)
       : DataLayoutDescription(dataLayoutString),
         UniversalLinkInfo(target, opts.HasMultipleIGMs, /*forcePublic*/ false,
-                          /*static=*/false),
+                          /*static=*/false, /*mergeableSymbols*/false),
         SwiftModule(swiftModule), Opts(opts), recorder(recorder),
         previousInstallNameMap(parsePreviousModuleInstallNameMap()) {}
 

test/embedded/linkage-linkonce-odr.swift

@@ -0,0 +1,36 @@
+// RUN: %empty-directory(%t)
+// RUN: %{python} %utils/split_file.py -o %t %s
+
+// RUN: %target-swift-frontend -mergeable-symbols -c -emit-module -o %t/MyModule.o %t/MyModule.swift   -enable-experimental-feature Embedded -parse-as-library
+// RUN: %target-swift-frontend -mergeable-symbols -c              -o %t/a.o        %t/Main.swift -I %t -enable-experimental-feature Embedded
+// RUN: %target-clang %t/a.o %t/MyModule.o -o %t/a.out
+// RUN: %target-run %t/a.out | %FileCheck %s
+
+// REQUIRES: swift_in_compiler
+// REQUIRES: executable_test
+// REQUIRES: OS=macosx || OS=linux-gnu
+// REQUIRES: swift_feature_Embedded
+
+// BEGIN MyModule.swift
+
+public func module_func() {
+  print("module_func")
+}
+
+public func module_generic_func<T: CustomStringConvertible>(t: T) {
+  print("module_generic_func: \(t)")
+}
+
+// BEGIN Main.swift
+
+import MyModule
+
+func test() {
+  module_func()
+  module_generic_func(t: 42)
+}
+
+test()
+
+// CHECK: module_func
+// CHECK: module_generic_func: 42