SIL: remove some dead code from SILCloner

NFC

Author: eeckstein

include/swift/SIL/SILCloner.h

@@ -67,9 +67,6 @@ class SILCloner : protected SILInstructionVisitor<ImplClass> {
   // convenient way to iterate over the cloned region.
   SmallVector<SILBasicBlock *, 8> preorderBlocks;
 
-  /// Set of basic blocks where unreachable was inserted.
-  SmallPtrSet<SILBasicBlock *, 32> BlocksWithUnreachables;
-
   // Keep track of the last cloned block in function order. For single block
   // regions, this will be the start block.
   SILBasicBlock *lastClonedBB = nullptr;
@@ -97,7 +94,6 @@ class SILCloner : protected SILInstructionVisitor<ImplClass> {
     ValueMap.clear();
     BBMap.clear();
     preorderBlocks.clear();
-    BlocksWithUnreachables.clear();
   }
 
   /// Clients of SILCloner who want to know about any newly created
@@ -170,12 +166,6 @@ class SILCloner : protected SILInstructionVisitor<ImplClass> {
     asImpl().mapValue(origValue, mappedValue);
   }
 
-  /// Mark a block containing an unreachable instruction for use in the `fixUp`
-  /// callback.
-  void addBlockWithUnreachable(SILBasicBlock *BB) {
-    BlocksWithUnreachables.insert(BB);
-  }
-
   /// Register a re-mapping for opened existentials.
   void registerOpenedExistentialRemapping(ArchetypeType *From,
                                           ArchetypeType *To) {
@@ -787,32 +777,6 @@ SILCloner<ImplClass>::doFixUp(SILFunction *F) {
     }
   }
 
-  // Remove any code after unreachable instructions.
-
-  // NOTE: It is unfortunate that it essentially duplicates the code from
-  // sil-combine, but doing so allows for avoiding any cross-layer invocations
-  // between SIL and SILOptimizer layers.
-
-  for (auto *BB : BlocksWithUnreachables) {
-    for (auto &I : *BB) {
-      if (!isa<UnreachableInst>(&I))
-        continue;
-
-      // Collect together all the instructions after this point
-      llvm::SmallVector<SILInstruction *, 32> ToRemove;
-      for (auto Inst = BB->rbegin(); &*Inst != &I; ++Inst)
-        ToRemove.push_back(&*Inst);
-
-      for (auto *Inst : ToRemove) {
-        // Replace any non-dead results with SILUndef values
-        Inst->replaceAllUsesOfAllResultsWithUndef();
-        Inst->eraseFromParent();
-      }
-    }
-  }
-
-  BlocksWithUnreachables.clear();
-
   // Call any cleanup specific to the CRTP extensions.
   asImpl().fixUp(F);
 }

include/swift/SIL/TypeSubstCloner.h

@@ -137,7 +137,6 @@ class TypeSubstCloner : public SILClonerWithScopes<ImplClass> {
   using SILClonerWithScopes<ImplClass>::getOpBasicBlock;
   using SILClonerWithScopes<ImplClass>::recordClonedInstruction;
   using SILClonerWithScopes<ImplClass>::recordFoldedValue;
-  using SILClonerWithScopes<ImplClass>::addBlockWithUnreachable;
   using SILClonerWithScopes<ImplClass>::OpenedArchetypesTracker;
 
   TypeSubstCloner(SILFunction &To,