Cleanup: Make CheckClassId instruction more general so it

runtime/vm/simulator_dbc.cc

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include <setjmp.h>  // NOLINT
 #include <stdlib.h>
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_DBC)
 
@@ skipping 3236 matching lines @@
   {
     BYTECODE(CheckClassId, A_D);
     const intptr_t actual_cid =
         reinterpret_cast<intptr_t>(FP[rA]) >> kSmiTagSize;
     const intptr_t desired_cid = rD;
     pc += (actual_cid == desired_cid) ? 1 : 0;
     DISPATCH();
   }
 
   {
+    BYTECODE(CheckClassIdRange, A_B_C);
+    const intptr_t actual_cid =
+        reinterpret_cast<intptr_t>(FP[rA]) >> kSmiTagSize;
+    const uintptr_t cid_start = rB;
+    const uintptr_t cid_end = rC;
+    // Unsigned comparison.
+    pc += (actual_cid - cid_start <= cid_end + 1u - cid_start) ? 1 : 0;

[kustermann, 2017/05/18 09:59:45]

If

  [cid_start, cid_end] = [0, 1]
  actual_cid = 2

This translates to

  2 - 0 <= 1 + 1 - 0
  2     <= 2

despite actual_cid not in [cid_start, cid_end]!

[erikcorry, 2017/05/18 14:25:30]

Oops, fixed.

+    DISPATCH();
+  }
+
+  {
     BYTECODE(CheckBitTest, A_D);
     const intptr_t raw_value = reinterpret_cast<intptr_t>(FP[rA]);
     const bool is_smi = ((raw_value & kSmiTagMask) == kSmiTag);
     const intptr_t cid_min = Bytecode::DecodeD(*pc);
     const intptr_t cid_mask =
         Smi::Value(RAW_CAST(Smi, LOAD_CONSTANT(Bytecode::DecodeD(*(pc + 1)))));
     if (LIKELY(!is_smi)) {
       const intptr_t cid_max = Utils::HighestBit(cid_mask) + cid_min;
       const intptr_t cid = SimulatorHelpers::GetClassId(FP[rA]);
       // The cid is in-bounds, and the bit is set in the mask.
@@ skipping 616 matching lines @@
     pc_ = pc;
   }
 
   buf->Longjmp();
   UNREACHABLE();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_DBC