Support for eliminated witness methods in SILWitnessTable.

A method entry in SILWitnessTable can now be null. This will be needed by dead method elimination. Swift SVN r22914
iLevi · Oct 24, 2014 · 60cb1a6 · 60cb1a6
1 parent 6786969
commit 60cb1a6
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Showing 12 changed files with 91 additions and 23 deletions.
diff --git a/include/swift/SIL/SILWitnessTable.h b/include/swift/SIL/SILWitnessTable.h
@@ -47,6 +47,7 @@ class SILWitnessTable : public llvm::ilist_node<SILWitnessTable>,
     /// The method required.
     SILDeclRef Requirement;
     /// The witness for the method.
+    /// This can be null in case dead function elimination has removed the method.
     SILFunction *Witness;
   };
 

diff --git a/include/swift/Serialization/ModuleFormat.h b/include/swift/Serialization/ModuleFormat.h
@@ -51,7 +51,7 @@ const uint16_t VERSION_MAJOR = 0;
 /// To ensure that two separate changes don't silently get merged into one
 /// in source control, you should also update the comment to briefly
 /// describe what change you made.
-const uint16_t VERSION_MINOR = 156; // Last change: add fragile flag for witness tables
+const uint16_t VERSION_MINOR = 157; // Last change: support nil in witness method entry
 
 using DeclID = Fixnum<31>;
 using DeclIDField = BCFixed<31>;

diff --git a/lib/IRGen/GenProto.cpp b/lib/IRGen/GenProto.cpp
@@ -3096,10 +3096,14 @@ namespace {
       assert(entry.getMethodWitness().Requirement.getDecl() == iface
              && "sil witness table does not match protocol");
 
-      llvm::Constant *witness
-        = IGM.getAddrOfSILFunction(entry.getMethodWitness().Witness,
-                                   NotForDefinition);
-      witness = llvm::ConstantExpr::getBitCast(witness, IGM.Int8PtrTy);
+      SILFunction *Func = entry.getMethodWitness().Witness;
+      llvm::Constant *witness = nullptr;
+      if (Func) {
+        witness = IGM.getAddrOfSILFunction(Func, NotForDefinition);
+        witness = llvm::ConstantExpr::getBitCast(witness, IGM.Int8PtrTy);
+      } else {
+        witness = llvm::ConstantPointerNull::get(IGM.Int8PtrTy);
+      }
       Table.push_back(witness);
       return;
     }

diff --git a/lib/Parse/ParseSIL.cpp b/lib/Parse/ParseSIL.cpp
@@ -3880,15 +3880,23 @@ bool Parser::parseSILWitnessTable() {
       Identifier FuncName;
       SourceLoc FuncLoc;
       if (WitnessState.parseSILDeclRef(Ref) ||
-          parseToken(tok::colon, diag::expected_sil_witness_colon) ||
-          parseToken(tok::at_sign, diag::expected_sil_function_name) ||
-          WitnessState.parseSILIdentifier(FuncName, FuncLoc,
-                                          diag::expected_sil_value_name))
-        return true;
-      SILFunction *Func = SIL->M->lookUpFunction(FuncName.str());
-      if (!Func) {
-        diagnose(FuncLoc, diag::sil_witness_func_not_found, FuncName);
+          parseToken(tok::colon, diag::expected_sil_witness_colon))
         return true;
+
+      SILFunction *Func = nullptr;
+      if (Tok.is(tok::kw_nil)) {
+        consumeToken();
+      } else {
+        if (parseToken(tok::at_sign, diag::expected_sil_function_name) ||
+            WitnessState.parseSILIdentifier(FuncName, FuncLoc,
+                                        diag::expected_sil_value_name))
+          return true;
+
+        Func = SIL->M->lookUpFunction(FuncName.str());
+        if (!Func) {
+          diagnose(FuncLoc, diag::sil_witness_func_not_found, FuncName);
+          return true;
+        }
       }
       witnessEntries.push_back(SILWitnessTable::MethodWitness{
         Ref, Func

diff --git a/lib/SIL/SILModule.cpp b/lib/SIL/SILModule.cpp
@@ -524,6 +524,10 @@ class SILLinkerVisitor : public SILInstructionVisitor<SILLinkerVisitor, bool> {
         if (Member.hasValue() && E.getMethodWitness().Requirement != *Member)
           continue;
 
+        // The witness could be removed by dead function elimination.
+        if (!E.getMethodWitness().Witness)
+          continue;
+
         // Otherwise if it is the requirement we are looking for or we just want
         // to deserialize everything, add the function to the list of functions
         // to deserialize.

diff --git a/lib/SIL/SILPrinter.cpp b/lib/SIL/SILPrinter.cpp
@@ -1634,9 +1634,13 @@ void SILWitnessTable::print(llvm::raw_ostream &OS, bool Verbose) const {
       OS << "method ";
       methodWitness.Requirement.print(OS);
       OS << ": ";
-      methodWitness.Witness->printName(OS);
-      OS << "\t// "
-         << demangleSymbolAsString(methodWitness.Witness->getName());
+      if (methodWitness.Witness) {
+        methodWitness.Witness->printName(OS);
+        OS << "\t// "
+           << demangleSymbolAsString(methodWitness.Witness->getName());
+      } else {
+        OS << "nil";
+      }
       break;
     }
     case AssociatedType: {

diff --git a/lib/SIL/SILWitnessTable.cpp b/lib/SIL/SILWitnessTable.cpp
@@ -118,7 +118,9 @@ SILWitnessTable::~SILWitnessTable() {
   for (auto entry : getEntries()) {
     switch (entry.getKind()) {
     case Method:
-      entry.getMethodWitness().Witness->decrementRefCount();
+      if (entry.getMethodWitness().Witness) {
+        entry.getMethodWitness().Witness->decrementRefCount();
+      }
       break;
     case AssociatedType:
     case AssociatedTypeProtocol:
@@ -144,7 +146,9 @@ void SILWitnessTable::convertToDefinition(ArrayRef<Entry> entries,
   for (auto entry : getEntries()) {
     switch (entry.getKind()) {
     case Method:
-      entry.getMethodWitness().Witness->incrementRefCount();
+      if (entry.getMethodWitness().Witness) {
+        entry.getMethodWitness().Witness->incrementRefCount();
+      }
       break;
     case AssociatedType:
     case AssociatedTypeProtocol:

diff --git a/lib/SIL/Verifier.cpp b/lib/SIL/Verifier.cpp
@@ -2454,8 +2454,10 @@ void SILWitnessTable::verify(const SILModule &M) const {
   for (const Entry &E : getEntries())
     if (E.getKind() == SILWitnessTable::WitnessKind::Method) {
       SILFunction *F = E.getMethodWitness().Witness;
-      assert(!isLessVisibleThan(F->getLinkage(), getLinkage()) &&
-             "Witness tables should not reference less visible functions.");
+      if (F) {
+        assert(!isLessVisibleThan(F->getLinkage(), getLinkage()) &&
+               "Witness tables should not reference less visible functions.");
+      }
     }
 #endif
 }

diff --git a/lib/Serialization/DeserializeSIL.cpp b/lib/Serialization/DeserializeSIL.cpp
@@ -1936,8 +1936,11 @@ SILWitnessTable *SILDeserializer::readWitnessTable(DeclID WId,
       ArrayRef<uint64_t> ListOfValues;
       DeclID NameID;
       WitnessMethodEntryLayout::readRecord(scratch, NameID, ListOfValues);
-      SILFunction *Func = getFuncForReference(MF->getIdentifier(NameID).str());
-      if (Func) {
+      SILFunction *Func = nullptr;
+      if (NameID != 0) {
+        Func = getFuncForReference(MF->getIdentifier(NameID).str());
+      }
+      if (Func || NameID == 0) {
         unsigned NextValueIndex = 0;
         witnessEntries.push_back(SILWitnessTable::MethodWitness{
           getSILDeclRef(MF, ListOfValues, NextValueIndex), Func

diff --git a/lib/Serialization/SerializeSIL.cpp b/lib/Serialization/SerializeSIL.cpp
@@ -1477,10 +1477,14 @@ void SILSerializer::writeSILWitnessTable(const SILWitnessTable &wt) {
     SmallVector<ValueID, 4> ListOfValues;
     handleSILDeclRef(S, methodWitness.Requirement, ListOfValues);
     FuncsToDeclare.insert(methodWitness.Witness);
+    IdentifierID witnessID = 0;
+    if (SILFunction *witness = methodWitness.Witness) {
+      witnessID = S.addIdentifierRef(Ctx.getIdentifier(witness->getName()));
+    }
     WitnessMethodEntryLayout::emitRecord(Out, ScratchRecord,
         SILAbbrCodes[WitnessMethodEntryLayout::Code],
         // SILFunction name
-        S.addIdentifierRef(Ctx.getIdentifier(methodWitness.Witness->getName())),
+        witnessID,
         ListOfValues);
   }
 }

diff --git a/test/SIL/Parser/witness_tables.sil b/test/SIL/Parser/witness_tables.sil
@@ -79,3 +79,20 @@ sil_witness_table public_external InheritedConformance2: InheritedProtocol1 modu
 // CHECK-LABEL: sil_witness_table public InheritedConformance2: AnyProtocol module witness_tables
 // CHECK-NOT: }
 sil_witness_table public InheritedConformance2: AnyProtocol module witness_tables
+
+
+protocol Proto {
+	func abc()
+}
+
+class DeadMethodClass : Proto {
+	func abc()
+}
+
+// CHECK-LABEL: sil_witness_table DeadMethodClass: Proto module witness_tables
+// CHECK: method #Proto.abc!1: nil
+// CHECK: }
+sil_witness_table DeadMethodClass: Proto module witness_tables {
+  method #Proto.abc!1: nil
+}
+
diff --git a/test/SIL/Serialization/witness_tables.sil b/test/SIL/Serialization/witness_tables.sil
@@ -79,3 +79,20 @@ sil_witness_table InheritedConformance2: InheritedProtocol1 module witness_table
 // CHECK-LABEL: sil_witness_table InheritedConformance2: AnyProtocol module witness_tables
 // CHECK-NOT: }
 sil_witness_table InheritedConformance2: AnyProtocol module witness_tables
+
+
+protocol Proto {
+	func abc()
+}
+
+class DeadMethodClass : Proto {
+	func abc()
+}
+
+// CHECK-LABEL: sil_witness_table DeadMethodClass: Proto module witness_tables
+// CHECK: method #Proto.abc!1: nil
+// CHECK: }
+sil_witness_table DeadMethodClass: Proto module witness_tables {
+  method #Proto.abc!1: nil
+}
+