Fix generic specialization that can result in noreturn apply without unreachable

rdar://50393169

Author: aschwaighofer

include/swift/SIL/TypeSubstCloner.h

@@ -193,6 +193,13 @@ class TypeSubstCloner : public SILClonerWithScopes<ImplClass> {
                                  Helper.getArguments(), Inst->isNonThrowing(),
                                  GenericSpecializationInformation::create(
                                    Inst, getBuilder()));
+    // Specialization can return noreturn applies that were not identified as
+    // such before.
+    if (N->isCalleeNoReturn() &&
+        !isa<UnreachableInst>(*std::next(SILBasicBlock::iterator(Inst)))) {
+      noReturnApplies.push_back(N);
+    }
+
     recordClonedInstruction(Inst, N);
   }
 
@@ -381,6 +388,9 @@ class TypeSubstCloner : public SILClonerWithScopes<ImplClass> {
   SILFunction &Original;
   /// True, if used for inlining.
   bool Inlining;
+  // Generic specialization can create noreturn applications that where
+  // previously not identifiable as such.
+  SmallVector<ApplyInst *, 16> noReturnApplies;
 };
 
 } // end namespace swift

include/swift/SILOptimizer/Utils/GenericCloner.h

@@ -74,6 +74,8 @@ class GenericCloner
     return SC.getCloned();
   }
 
+  void fixUp(SILFunction *calleeFunction);
+
 protected:
   void visitTerminator(SILBasicBlock *BB);
 

lib/SILOptimizer/Utils/GenericCloner.cpp

@@ -191,3 +191,12 @@ const SILDebugScope *GenericCloner::remapScope(const SILDebugScope *DS) {
   RemappedScopeCache.insert({DS, RemappedScope});
   return RemappedScope;
 }
+
+void GenericCloner::fixUp(SILFunction *f) {
+  for (auto *apply : noReturnApplies) {
+    auto applyBlock = apply->getParent();
+    applyBlock->split(std::next(SILBasicBlock::iterator(apply)));
+    getBuilder().setInsertionPoint(applyBlock);
+    getBuilder().createUnreachable(apply->getLoc());
+  }
+}