Simplification: remove builtin "destroyArray" with trivial element types

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/SimplifyBuiltin.swift

@@ -32,8 +32,15 @@ extension BuiltinInst : OnoneSimplifyable {
            .Strideof,
            .Alignof:
         optimizeTargetTypeConst(context)
-      case .DestroyArray,
-           .CopyArray,
+      case .DestroyArray:
+        if let elementType = substitutionMap.replacementTypes[0],
+           elementType.isTrivial(in: parentFunction)
+        {
+          context.erase(instruction: self)
+          return
+        }
+        optimizeArgumentToThinMetatype(argument: 0, context)
+      case .CopyArray,
            .TakeArrayNoAlias,
            .TakeArrayFrontToBack,
            .TakeArrayBackToFront,

test/SILOptimizer/simplify_builtin.sil

@@ -605,3 +605,12 @@ bb0(%0 : $Builtin.RawPointer, %1 : $Builtin.Word):
   return %0 : $Builtin.RawPointer
 }
 
+// CHECK-LABEL: sil @remove_trivial_destroy_array
+// CHECK-NOT:     builtin
+// CHECK:       } // end sil function 'remove_trivial_destroy_array'
+sil @remove_trivial_destroy_array : $@convention(thin) (Builtin.RawPointer, Builtin.Word) -> Builtin.RawPointer {
+bb0(%0 : $Builtin.RawPointer, %1 : $Builtin.Word):
+  %2 = metatype $@thin Int.Type
+  %3 = builtin "destroyArray"<Int>(%2 : $@thin Int.Type, %0 : $Builtin.RawPointer, %1 : $Builtin.Word) : $()
+  return %0 : $Builtin.RawPointer
+}