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

src/mips/code-stubs-mips.cc

Index: src/mips/code-stubs-mips.cc
diff --git a/src/mips/code-stubs-mips.cc b/src/mips/code-stubs-mips.cc
index 9da0a921803b0240e97175a22450733035c112d0..0ce6f7d1a602a79eff225dcdbd926e038ab7bb7f 100644
--- a/src/mips/code-stubs-mips.cc
+++ b/src/mips/code-stubs-mips.cc
@@ -1602,7 +1602,6 @@ void FunctionPrototypeStub::Generate(MacroAssembler* masm) {
       masm, PropertyAccessCompiler::MissBuiltin(Code::LOAD_IC));
 }
 
-
 void RegExpExecStub::Generate(MacroAssembler* masm) {
   // Just jump directly to runtime if native RegExp is not selected at compile
   // time or if regexp entry in generated code is turned off runtime switch or
@@ -1635,8 +1634,7 @@ void RegExpExecStub::Generate(MacroAssembler* masm) {
 
   // Ensure that a RegExp stack is allocated.
   ExternalReference address_of_regexp_stack_memory_address =
-      ExternalReference::address_of_regexp_stack_memory_address(
-          isolate());
+      ExternalReference::address_of_regexp_stack_memory_address(isolate());
   ExternalReference address_of_regexp_stack_memory_size =
       ExternalReference::address_of_regexp_stack_memory_size(isolate());
   __ li(a0, Operand(address_of_regexp_stack_memory_size));
@@ -1688,34 +1686,33 @@ void RegExpExecStub::Generate(MacroAssembler* masm) {
   __ lw(subject, MemOperand(sp, kSubjectOffset));
   __ JumpIfSmi(subject, &runtime);
   __ mov(a3, subject);  // Make a copy of the original subject string.
-  __ lw(a0, FieldMemOperand(subject, HeapObject::kMapOffset));
-  __ lbu(a0, FieldMemOperand(a0, Map::kInstanceTypeOffset));
   // subject: subject string
   // a3: subject string
-  // a0: subject string instance type
   // regexp_data: RegExp data (FixedArray)
   // Handle subject string according to its encoding and representation:
-  // (1) Sequential string?  If yes, go to (5).
-  // (2) Anything but sequential or cons?  If yes, go to (6).
-  // (3) Cons string.  If the string is flat, replace subject with first string.
-  //     Otherwise bailout.
-  // (4) Is subject external?  If yes, go to (7).
-  // (5) Sequential string.  Load regexp code according to encoding.
+  // (1) Sequential string?  If yes, go to (4).
+  // (2) Sequential or cons?  If not, go to (5).
+  // (3) Cons string.  If the string is flat, replace subject with first string
+  //     and go to (1). Otherwise bail out to runtime.
+  // (4) Sequential string.  Load regexp code according to encoding.
   // (E) Carry on.
   /// [...]
 
   // Deferred code at the end of the stub:
-  // (6) Not a long external string?  If yes, go to (8).
-  // (7) External string.  Make it, offset-wise, look like a sequential string.
-  //     Go to (5).
-  // (8) Short external string or not a string?  If yes, bail out to runtime.
-  // (9) Sliced string.  Replace subject with parent.  Go to (4).
+  // (5) Long external string?  If not, go to (7).
+  // (6) External string.  Make it, offset-wise, look like a sequential string.
+  //     Go to (4).
+  // (7) Short external string or not a string?  If yes, bail out to runtime.
+  // (8) Sliced string.  Replace subject with parent.  Go to (1).
 
-  Label seq_string /* 5 */, external_string /* 7 */,
-        check_underlying /* 4 */, not_seq_nor_cons /* 6 */,
-        not_long_external /* 8 */;
+  Label seq_string /* 4 */, external_string /* 6 */, check_underlying /* 1 */,
+      not_seq_nor_cons /* 5 */, not_long_external /* 7 */;
+
+  __ bind(&check_underlying);
+  __ lw(a0, FieldMemOperand(subject, HeapObject::kMapOffset));
+  __ lbu(a0, FieldMemOperand(a0, Map::kInstanceTypeOffset));
 
-  // (1) Sequential string?  If yes, go to (5).
+  // (1) Sequential string?  If yes, go to (4).
   __ And(a1,
          a0,
          Operand(kIsNotStringMask |
@@ -1724,12 +1721,12 @@ void RegExpExecStub::Generate(MacroAssembler* masm) {
   STATIC_ASSERT((kStringTag | kSeqStringTag) == 0);
   __ Branch(&seq_string, eq, a1, Operand(zero_reg));  // Go to (5).
 
-  // (2) Anything but sequential or cons?  If yes, go to (6).
+  // (2) Sequential or cons?  If not, go to (5).
   STATIC_ASSERT(kConsStringTag < kExternalStringTag);
   STATIC_ASSERT(kSlicedStringTag > kExternalStringTag);
   STATIC_ASSERT(kIsNotStringMask > kExternalStringTag);
   STATIC_ASSERT(kShortExternalStringTag > kExternalStringTag);
-  // Go to (6).
+  // Go to (5).
   __ Branch(&not_seq_nor_cons, ge, a1, Operand(kExternalStringTag));
 
   // (3) Cons string.  Check that it's flat.
@@ -1738,19 +1735,9 @@ void RegExpExecStub::Generate(MacroAssembler* masm) {
   __ LoadRoot(a1, Heap::kempty_stringRootIndex);
   __ Branch(&runtime, ne, a0, Operand(a1));
   __ lw(subject, FieldMemOperand(subject, ConsString::kFirstOffset));
+  __ jmp(&check_underlying);
 
-  // (4) Is subject external?  If yes, go to (7).
-  __ bind(&check_underlying);
-  __ lw(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.
+  // (4) Sequential string.  Load regexp code according to encoding.
   __ bind(&seq_string);
   // subject: sequential subject string (or look-alike, external string)
   // a3: original subject string
@@ -1992,12 +1979,12 @@ void RegExpExecStub::Generate(MacroAssembler* masm) {
   __ TailCallRuntime(Runtime::kRegExpExec);
 
   // Deferred code for string handling.
-  // (6) Not a long external string?  If yes, go to (8).
+  // (5) Long external string?  If not, go to (7).
   __ bind(&not_seq_nor_cons);
-  // Go to (8).
+  // Go to (7).
   __ Branch(&not_long_external, gt, a1, Operand(kExternalStringTag));
 
-  // (7) External string.  Make it, offset-wise, look like a sequential string.
+  // (6) External string.  Make it, offset-wise, look like a sequential string.
   __ bind(&external_string);
   __ lw(a0, FieldMemOperand(subject, HeapObject::kMapOffset));
   __ lbu(a0, FieldMemOperand(a0, Map::kInstanceTypeOffset));
@@ -2019,13 +2006,13 @@ void RegExpExecStub::Generate(MacroAssembler* masm) {
           SeqTwoByteString::kHeaderSize - kHeapObjectTag);
   __ jmp(&seq_string);    // Go to (5).
 
-  // (8) Short external string or not a string?  If yes, bail out to runtime.
+  // (7) Short external string or not a string?  If yes, bail out to runtime.
   __ bind(&not_long_external);
   STATIC_ASSERT(kNotStringTag != 0 && kShortExternalStringTag !=0);
   __ And(at, a1, Operand(kIsNotStringMask | kShortExternalStringMask));
   __ Branch(&runtime, ne, at, Operand(zero_reg));
 
-  // (9) Sliced string.  Replace subject with parent.  Go to (4).
+  // (8) Sliced string.  Replace subject with parent.  Go to (4).
   // Load offset into t0 and replace subject string with parent.
   __ lw(t0, FieldMemOperand(subject, SlicedString::kOffsetOffset));
   __ sra(t0, t0, kSmiTagSize);