Disable dead conformance elimination for now.

There are still several open issues (e.g. asserts in IRGen) and it seems to be hard to fix them.
Most likely we’ll go for a different approach at all.

Author: eeckstein

include/swift/SIL/InstructionUtils.h

@@ -123,6 +123,13 @@ class ConformanceCollector {
 
   ConformanceCollector(SILModule &M) : M(M) { }
 
+#ifndef NDEBUG
+  static bool verifyInIRGen() {
+    // TODO: currently disabled because of several problems.
+    return false;
+  }
+#endif
+
   /// Collect all used conformances of an instruction.
   ///
   /// If the instruction can escape a metatype, also record this metatype.

lib/IRGen/GenDecl.cpp

@@ -1856,6 +1856,9 @@ IRGenModule::getAddrOfLLVMVariable(LinkEntity entity, Alignment alignment,
 
 void IRGenModule::checkEligibleConf(const ProtocolConformance *Conf) {
 #ifndef NDEBUG
+  if (!ConformanceCollector::verifyInIRGen())
+    return;
+
   if (EligibleConfs.isUsed(Conf))
     return;
 
@@ -1876,6 +1879,9 @@ void IRGenModule::checkEligibleConf(const ProtocolConformance *Conf) {
 
 void IRGenModule::checkEligibleMetaType(NominalTypeDecl *NT) {
 #ifndef NDEBUG
+  if (!ConformanceCollector::verifyInIRGen())
+    return;
+
   if (!NT || EligibleConfs.isMetaTypeEscaping(NT))
     return;
 

lib/SILOptimizer/IPO/DeadFunctionElimination.cpp

@@ -28,6 +28,10 @@ using namespace swift;
 STATISTIC(NumDeadFunc, "Number of dead functions eliminated");
 STATISTIC(NumEliminatedExternalDefs, "Number of external function definitions eliminated");
 
+llvm::cl::opt<bool> RemoveDeadConformances(
+    "remove-dead-conformances", llvm::cl::init(false),
+    llvm::cl::desc("Remove dead conformances"));
+
 namespace {
 
 /// This is a base class for passes that are based on function liveness
@@ -318,7 +322,8 @@ class FunctionLivenessComputation {
         } else if (auto *FRI = dyn_cast<FunctionRefInst>(&I)) {
           ensureAlive(FRI->getReferencedFunction());
         }
-        FoundConformances.collect(&I);
+        if (RemoveDeadConformances)
+          FoundConformances.collect(&I);
       }
     }
     // Now we scan all _new_ conformances we found in the function.
@@ -546,7 +551,7 @@ class DeadFunctionElimination : FunctionLivenessComputation {
 
       ProtocolConformance *C = WT.getConformance();
       CanType ConformingTy = C->getType()->getCanonicalType();
-      if (ConformingTy.isAnyClassReferenceType()) {
+      if (!RemoveDeadConformances || ConformingTy.isAnyClassReferenceType()) {
         // We are very conservative with class conformances. Even if a private/
         // internal class is never instantiated, it might be created via
         // reflection by using the stdlib's _getTypeByMangledName function.

test/SILOptimizer/dead_conformance.sil

@@ -1,4 +1,4 @@
-// RUN: %target-sil-opt -assume-parsing-unqualified-ownership-sil -enable-sil-verify-all -sil-deadfuncelim %s | %FileCheck %s
+// RUN: %target-sil-opt -remove-dead-conformances -assume-parsing-unqualified-ownership-sil -enable-sil-verify-all -sil-deadfuncelim %s | %FileCheck %s
 
 sil_stage canonical