Remove MergePartialModules from SILOptions

Its use in deserialization can be replaced with a
more general check for whether we're deserializing
into the same module. Its use in the SILVerifier
is subsumed by the check for whether the SILModule
is canonical, which it isn't during merge-modules.

Author: hamishknight

include/swift/AST/SILOptions.h

@@ -40,11 +40,6 @@ class SILOptions {
   /// Controls the aggressiveness of the loop unroller.
   int UnrollThreshold = 250;
 
-  /// Controls whether to pull in SIL from partial modules during the
-  /// merge modules step. Could perhaps be merged with the link mode
-  /// above but the interactions between all the flags are tricky.
-  bool MergePartialModules = false;
-
   /// Remove all runtime assertions during optimizations.
   bool RemoveRuntimeAsserts = false;
 

lib/Frontend/CompilerInvocation.cpp

@@ -1049,9 +1049,6 @@ static bool ParseSILArgs(SILOptions &Opts, ArgList &Args,
   if (FEOpts.RequestedAction == FrontendOptions::ActionType::EmitModuleOnly)
     Opts.StopOptimizationAfterSerialization = true;
 
-  if (Args.hasArg(OPT_sil_merge_partial_modules))
-    Opts.MergePartialModules = true;
-
   // Propagate the typechecker's understanding of
   // -experimental-skip-non-inlinable-function-bodies to SIL.
   Opts.SkipNonInlinableFunctionBodies = TCOpts.SkipNonInlinableFunctionBodies;

lib/SIL/Verifier/SILVerifier.cpp

@@ -1751,8 +1751,9 @@ class SILVerifier : public SILVerifierBase<SILVerifier> {
               "[dynamically_replaceable] function");
 
     // In canonical SIL, direct reference to a shared_external declaration
-    // is an error; we should have deserialized a body. In raw SIL, we may
-    // not have deserialized the body yet.
+    // is an error; we should have deserialized a body. In raw SIL, including
+    // the merge-modules phase, we may not have deserialized the body yet as we
+    // may not have run the SILLinker pass.
     if (F.getModule().getStage() >= SILStage::Canonical) {
       if (RefF->isExternalDeclaration()) {
         require(SingleFunction ||
@@ -5560,20 +5561,13 @@ void SILModule::verify() const {
   // Uniquing set to catch symbol name collisions.
   llvm::DenseSet<StringRef> symbolNames;
 
-  // When merging partial modules, we only link functions from the current
-  // module, without enabling "LinkAll" mode or running the SILLinker pass;
-  // in this case, we need to relax some of the checks.
-  bool SingleFunction = false;
-  if (getOptions().MergePartialModules)
-    SingleFunction = true;
-
   // Check all functions.
   for (const SILFunction &f : *this) {
     if (!symbolNames.insert(f.getName()).second) {
       llvm::errs() << "Symbol redefined: " << f.getName() << "!\n";
       assert(false && "triggering standard assertion failure routine");
     }
-    f.verify(SingleFunction);
+    f.verify(/*singleFunction*/ false);
   }
 
   // Check all globals.

lib/Serialization/DeserializeSIL.cpp

@@ -597,7 +597,13 @@ SILDeserializer::readSILFunctionChecked(DeclID FID, SILFunction *existingFn,
 
     fn->setSerialized(IsSerialized_t(isSerialized));
 
-    if (SILMod.getOptions().MergePartialModules)
+    // If the serialized function comes from the same module, we're merging
+    // modules, and can update the the linkage directly. This is needed to
+    // correctly update the linkage for forward declarations to entities defined
+    // in another file of the same module – we want to ensure the linkage
+    // reflects the fact that the entity isn't really external and shouldn't be
+    // dropped from the resulting merged module.
+    if (getFile()->getParentModule() == SILMod.getSwiftModule())
       fn->setLinkage(linkage);
 
     // Don't override the transparency or linkage of a function with