Cross module optimization

This is a first version of cross module optimization (CMO).

The basic idea for CMO is to use the existing library evolution compiler features, but in an automated way. A new SIL module pass "annotates" functions and types with @inlinable and @usableFromInline. This results in functions being serialized into the swiftmodule file and thus available for optimizations in client modules.
The annotation is done with a worklist-algorithm, starting from public functions and continuing with entities which are used from already selected functions. A heuristic performs a preselection on which functions to consider - currently just generic functions are selected.

The serializer then writes annotated functions (including function bodies) into the swiftmodule file of the compiled module. Client modules are able to de-serialize such functions from their imported modules and use them for optimiations, like generic specialization.

The optimization is gated by a new compiler option -cross-module-optimization (also available in the swift driver).
By default this option is off. Without turning the option on, this change is (almost) a NFC.

rdar://problem/22591518

Author: eeckstein

include/swift/AST/SILOptions.h

@@ -62,6 +62,9 @@ class SILOptions {
   /// Useful when you want to enable -O LLVM opts but not -O SIL opts.
   bool DisableSILPerfOptimizations = false;
 
+  /// Controls whether cross module optimization is enabled.
+  bool CrossModuleOptimization = false;
+  
   /// Controls whether or not paranoid verification checks are run.
   bool VerifyAll = false;
 

include/swift/Option/Options.td

@@ -589,6 +589,10 @@ def Oplayground : Flag<["-"], "Oplayground">, Group<O_Group>,
   Flags<[HelpHidden, FrontendOption, ModuleInterfaceOption]>,
   HelpText<"Compile with optimizations appropriate for a playground">;
 
+def CrossModuleOptimization : Flag<["-"], "cross-module-optimization">,
+  Flags<[HelpHidden, FrontendOption]>,
+  HelpText<"Perform cross-module optimization">;
+
 def RemoveRuntimeAsserts : Flag<["-"], "remove-runtime-asserts">,
   Flags<[FrontendOption]>,
   HelpText<"Remove runtime safety checks.">;

include/swift/SILOptimizer/PassManager/Passes.def

@@ -64,6 +64,8 @@ PASS(AccessEnforcementSelection, "access-enforcement-selection",
      "Access Enforcement Selection")
 PASS(AccessEnforcementWMO, "access-enforcement-wmo",
      "Access Enforcement Whole Module Optimization")
+PASS(CrossModuleSerializationSetup, "cross-module-serialization-setup",
+     "Setup serialization flags for cross-module optimization")
 PASS(AccessSummaryDumper, "access-summary-dump",
      "Dump Address Parameter Access Summary")
 PASS(AccessedStorageDumper, "accessed-storage-dump",

lib/AST/Decl.cpp

@@ -2995,7 +2995,7 @@ SourceLoc ValueDecl::getAttributeInsertionLoc(bool forModifier) const {
 /// Returns true if \p VD needs to be treated as publicly-accessible
 /// at the SIL, LLVM, and machine levels due to being @usableFromInline.
 bool ValueDecl::isUsableFromInline() const {
-  assert(getFormalAccess() == AccessLevel::Internal);
+  assert(getFormalAccess() <= AccessLevel::Internal);
 
   if (getAttrs().hasAttribute<UsableFromInlineAttr>() ||
       getAttrs().hasAttribute<AlwaysEmitIntoClientAttr>() ||
@@ -3092,7 +3092,7 @@ static AccessLevel getAdjustedFormalAccess(const ValueDecl *VD,
     return getMaximallyOpenAccessFor(VD);
 
   if (treatUsableFromInlineAsPublic &&
-      access == AccessLevel::Internal &&
+      (access == AccessLevel::Internal || access == AccessLevel::Private) &&
       VD->isUsableFromInline()) {
     return AccessLevel::Public;
   }

lib/Driver/ToolChains.cpp

@@ -400,6 +400,10 @@ ToolChain::constructInvocation(const CompileJobAction &job,
   Arguments.push_back("-module-name");
   Arguments.push_back(context.Args.MakeArgString(context.OI.ModuleName));
 
+  if (context.Args.hasArg(options::OPT_CrossModuleOptimization)) {
+    Arguments.push_back("-cross-module-optimization");
+  }
+                                 
   addOutputsOfType(Arguments, context.Output, context.Args,
                    file_types::TY_OptRecord, "-save-optimization-record-path");
 

lib/Frontend/CompilerInvocation.cpp

@@ -871,6 +871,7 @@ static bool ParseSILArgs(SILOptions &Opts, ArgList &Args,
   Opts.EnableARCOptimizations &= !Args.hasArg(OPT_disable_arc_opts);
   Opts.EnableOSSAOptimizations &= !Args.hasArg(OPT_disable_ossa_opts);
   Opts.DisableSILPerfOptimizations |= Args.hasArg(OPT_disable_sil_perf_optzns);
+  Opts.CrossModuleOptimization |= Args.hasArg(OPT_CrossModuleOptimization);
   Opts.VerifyAll |= Args.hasArg(OPT_sil_verify_all);
   Opts.DebugSerialization |= Args.hasArg(OPT_sil_debug_serialization);
   Opts.EmitVerboseSIL |= Args.hasArg(OPT_emit_verbose_sil);

lib/FrontendTool/FrontendTool.cpp

@@ -1394,6 +1394,9 @@ static bool validateTBDIfNeeded(CompilerInvocation &Invocation,
   if (!astGuaranteedToCorrespondToSIL ||
       !inputFileKindCanHaveTBDValidated(Invocation.getInputKind()))
     return false;
+    
+  if (Invocation.getSILOptions().CrossModuleOptimization)
+    return false;
 
   const auto &frontendOpts = Invocation.getFrontendOptions();
   auto mode = frontendOpts.ValidateTBDAgainstIR;

lib/IRGen/GenDecl.cpp

@@ -831,7 +831,8 @@ IRGenModule::getAddrOfParentContextDescriptor(DeclContext *from,
 
     // Wrap up private types in an anonymous context for the containing file
     // unit so that the runtime knows they have unstable identity.
-    if (!fromAnonymousContext && Type->isOutermostPrivateOrFilePrivateScope())
+    if (!fromAnonymousContext && Type->isOutermostPrivateOrFilePrivateScope()
+        && !Type->isUsableFromInline())
       return {getAddrOfAnonymousContextDescriptor(Type),
               ConstantReference::Direct};
   }

lib/SILOptimizer/IPO/CMakeLists.txt

@@ -2,6 +2,7 @@ silopt_register_sources(
   CapturePromotion.cpp
   CapturePropagation.cpp
   ClosureSpecializer.cpp
+  CrossModuleSerializationSetup.cpp
   DeadFunctionElimination.cpp
   EagerSpecializer.cpp
   GlobalOpt.cpp