[regexp] do not assume short external strings have a minimum size.

src/mips64/code-stubs-mips64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #if V8_TARGET_ARCH_MIPS64
 
 #include "src/code-stubs.h"
 #include "src/api-arguments.h"
 #include "src/bootstrapper.h"
 #include "src/codegen.h"
@@ skipping 1724 matching lines @@
   __ LoadRoot(a1, Heap::kempty_stringRootIndex);
   __ Branch(&runtime, ne, a0, Operand(a1));
   __ ld(subject, FieldMemOperand(subject, ConsString::kFirstOffset));
 
   // (4) Is subject external?  If yes, go to (7).
   __ bind(&check_underlying);
   __ ld(a0, FieldMemOperand(subject, HeapObject::kMapOffset));
   __ lbu(a0, FieldMemOperand(a0, Map::kInstanceTypeOffset));
   STATIC_ASSERT(kSeqStringTag == 0);
   __ And(at, a0, Operand(kStringRepresentationMask));
-  // The underlying external string is never a short external string.
-  STATIC_ASSERT(ExternalString::kMaxShortLength < ConsString::kMinLength);
-  STATIC_ASSERT(ExternalString::kMaxShortLength < SlicedString::kMinLength);
   __ Branch(&external_string, ne, at, Operand(zero_reg));  // Go to (7).
 
   // (5) Sequential string.  Load regexp code according to encoding.
   __ bind(&seq_string);
   // subject: sequential subject string (or look-alike, external string)
   // a3: original subject string
   // Load previous index and check range before a3 is overwritten.  We have to
   // use a3 instead of subject here because subject might have been only made
   // to look like a sequential string when it actually is an external string.
   __ ld(a1, MemOperand(sp, kPreviousIndexOffset));
@@ skipping 4020 matching lines @@
                            kStackUnwindSpace, kInvalidStackOffset,
                            return_value_operand, NULL);
 }
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_MIPS64