Add support for end_lifetime in DCE

Author: meg-gupta

lib/SILOptimizer/Transforms/DeadCodeElimination.cpp

@@ -45,10 +45,11 @@ namespace {
 // FIXME: Reconcile the similarities between this and
 //        isInstructionTriviallyDead.
 static bool seemsUseful(SILInstruction *I) {
-  // Even though begin_access/destroy_value/copy_value have side-effects, they
-  // can be DCE'ed if they do not have useful dependencies/reverse dependencies
+  // Even though begin_access/destroy_value/copy_value/end_lifetime have
+  // side-effects, they can be DCE'ed if they do not have useful
+  // dependencies/reverse dependencies
   if (isa<BeginAccessInst>(I) || isa<CopyValueInst>(I) ||
-      isa<DestroyValueInst>(I))
+      isa<DestroyValueInst>(I) || isa<EndLifetimeInst>(I))
     return false;
 
   // A load [copy] is okay to be DCE'ed if there are no useful dependencies
@@ -268,7 +269,8 @@ void DCE::markLive() {
         break;
       }
       case SILInstructionKind::DestroyValueInst:
-      case SILInstructionKind::EndBorrowInst: {
+      case SILInstructionKind::EndBorrowInst:
+      case SILInstructionKind::EndLifetimeInst: {
         // The instruction is live only if it's operand value is also live
         addReverseDependency(I.getOperand(0), &I);
         break;

test/SILOptimizer/dead_code_elimination_nontrivial_ossa.sil

@@ -611,3 +611,44 @@ bb3:
   return %9999 : $()
 }
 
+// CHECK-LABEL: sil [ossa] @dce_deadendlifetime1 :
+// CHECK-NOT: end_lifetime
+// CHECK-LABEL: } // end sil function 'dce_deadendlifetime1'
+sil [ossa] @dce_deadendlifetime1 : $@convention(thin) () -> () {
+bb0:
+  cond_br undef, bb1, bb2
+
+bb1:
+  br bb3(undef : $Klass)
+
+bb2:
+  br bb3(undef : $Klass)
+
+bb3(%2 : @owned $Klass):
+  end_lifetime %2 : $Klass
+  %res = tuple ()
+  return %res : $()
+}
+
+// CHECK-LABEL: sil [ossa] @dce_deadendlifetime2 :
+// CHECK-NOT: end_lifetime
+// CHECK-LABEL: } // end sil function 'dce_deadendlifetime2'
+sil [ossa] @dce_deadendlifetime2 : $@convention(thin) () -> () {
+bb0:
+  cond_br undef, bb1, bb2
+
+bb1:
+  br bb3(undef : $Klass)
+
+bb2:
+  br bb3(undef : $Klass)
+
+bb3(%2 : @owned $Klass):
+  br bb4(%2 : $Klass)
+
+bb4(%3 : @owned $Klass):
+  end_lifetime %3 : $Klass
+  %res = tuple ()
+  return %res : $()
+}
+