Fix assertion in InstructionDeleter::trackIfDead.

This assertion was triggering when deleting scope-ending operations whose
operand had been replaced with an undef:

   end_borrow undef

Related to rdar://156431548

This was triggered during simplify-cfg by after adding blocks to the worklist,
then later cleaning up dead instructions in the worklist blocks. I'm unable to
create a test case based on simplify-cfg because the assertion is completely
unrelated to the optimization that adds blocks to the worklist.

Author: atrick

lib/SILOptimizer/Utils/InstructionDeleter.cpp

@@ -187,9 +187,8 @@ bool InstructionDeleter::trackIfDead(SILInstruction *inst) {
   bool fixLifetime = inst->getFunction()->hasOwnership();
   if (isInstructionTriviallyDead(inst)
       || isScopeAffectingInstructionDead(inst, fixLifetime)) {
-    assert(!isIncidentalUse(inst) &&
-           (!isa<DestroyValueInst>(inst) ||
-            canTriviallyDeleteOSSAEndScopeInst(inst)) &&
+    assert(!isIncidentalUse(inst)
+           || canTriviallyDeleteOSSAEndScopeInst(inst) &&
            "Incidental uses cannot be removed in isolation. "
            "They would be removed iff the operand is dead");
     getCallbacks().notifyWillBeDeleted(inst);
@@ -356,6 +355,20 @@ static FunctionTest DeleterDeleteIfDeadTest(
       llvm::outs() << "deleteIfDead returned " << deleted << "\n";
       function.print(llvm::outs());
     });
+
+// Arguments:
+// - instruction: the instruction to delete
+// Dumps:
+// - the function
+static FunctionTest DeleterTrackIfDeadTest(
+    "deleter_track_if_dead", [](auto &function, auto &arguments, auto &test) {
+      auto *inst = arguments.takeInstruction();
+      InstructionDeleter deleter;
+      llvm::outs() << "Tracking " << *inst;
+      deleter.trackIfDead(inst);
+      deleter.cleanupDeadInstructions();
+      function.print(llvm::outs());
+    });
 } // namespace swift::test
 
 void InstructionDeleter::forceDeleteAndFixLifetimes(SILInstruction *inst) {

test/SILOptimizer/instruction_deleter.sil

@@ -57,3 +57,18 @@ sil [ossa] @doDeleteLoadTake : $() -> () {
   %retval = tuple ()
   return %retval : $()
 }
+
+// CHECK-LABEL: begin running test {{.*}} on trackEndBorrow
+// CHECK: Tracking   end_borrow undef : $C
+// CHECK: sil [ossa] @trackEndBorrow : $@convention(thin) () -> () {
+// CHECK: bb0:
+// CHECK-NOT: end_borrow
+// CHECK-LABEL: } // end sil function 'trackEndBorrow'
+// CHECK-LABEL: end running test {{.*}} on trackEndBorrow
+sil [ossa] @trackEndBorrow : $() -> () {
+bb0:
+  specify_test "deleter_track_if_dead @instruction"
+  end_borrow undef : $C
+  %retval = tuple ()
+  return %retval : $()
+}