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

src/arm/code-stubs-arm.cc

Index: src/arm/code-stubs-arm.cc
diff --git a/src/arm/code-stubs-arm.cc b/src/arm/code-stubs-arm.cc
index dcac50ff6d8134a525138faefd9418c7664b4ff6..de66eb850a3b8d65e07738bdcc441e8319574630 100644
--- a/src/arm/code-stubs-arm.cc
+++ b/src/arm/code-stubs-arm.cc
@@ -1577,34 +1577,33 @@ void RegExpExecStub::Generate(MacroAssembler* masm) {
   __ ldr(subject, MemOperand(sp, kSubjectOffset));
   __ JumpIfSmi(subject, &runtime);
   __ mov(r3, subject);  // Make a copy of the original subject string.
-  __ ldr(r0, FieldMemOperand(subject, HeapObject::kMapOffset));
-  __ ldrb(r0, FieldMemOperand(r0, Map::kInstanceTypeOffset));
   // subject: subject string
   // r3: subject string
-  // r0: 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 /* 4 */, external_string /* 6 */, check_underlying /* 1 */,
+      not_seq_nor_cons /* 5 */, not_long_external /* 7 */;
 
-  Label seq_string /* 5 */, external_string /* 7 */,
-        check_underlying /* 4 */, not_seq_nor_cons /* 6 */,
-        not_long_external /* 8 */;
+  __ bind(&check_underlying);
+  __ ldr(r0, FieldMemOperand(subject, HeapObject::kMapOffset));
+  __ ldrb(r0, FieldMemOperand(r0, Map::kInstanceTypeOffset));
 
-  // (1) Sequential string?  If yes, go to (5).
+  // (1) Sequential string?  If yes, go to (4).
   __ and_(r1,
           r0,
           Operand(kIsNotStringMask |
@@ -1612,15 +1611,15 @@ void RegExpExecStub::Generate(MacroAssembler* masm) {
                   kShortExternalStringMask),
           SetCC);
   STATIC_ASSERT((kStringTag | kSeqStringTag) == 0);
-  __ b(eq, &seq_string);  // Go to (5).
+  __ b(eq, &seq_string);  // Go to (4).
 
-  // (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);
   __ cmp(r1, Operand(kExternalStringTag));
-  __ b(ge, &not_seq_nor_cons);  // Go to (6).
+  __ b(ge, &not_seq_nor_cons);  // Go to (5).
 
   // (3) Cons string.  Check that it's flat.
   // Replace subject with first string and reload instance type.
@@ -1628,19 +1627,9 @@ void RegExpExecStub::Generate(MacroAssembler* masm) {
   __ CompareRoot(r0, Heap::kempty_stringRootIndex);
   __ b(ne, &runtime);
   __ ldr(subject, FieldMemOperand(subject, ConsString::kFirstOffset));
+  __ jmp(&check_underlying);
 
-  // (4) Is subject external?  If yes, go to (7).
-  __ bind(&check_underlying);
-  __ ldr(r0, FieldMemOperand(subject, HeapObject::kMapOffset));
-  __ ldrb(r0, FieldMemOperand(r0, Map::kInstanceTypeOffset));
-  STATIC_ASSERT(kSeqStringTag == 0);
-  __ tst(r0, Operand(kStringRepresentationMask));
-  // The underlying external string is never a short external string.
-  STATIC_ASSERT(ExternalString::kMaxShortLength < ConsString::kMinLength);
-  STATIC_ASSERT(ExternalString::kMaxShortLength < SlicedString::kMinLength);
-  __ b(ne, &external_string);  // 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)
   // r3: original subject string
@@ -1873,12 +1862,12 @@ 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);
   // Compare flags are still set.
-  __ b(gt, &not_long_external);  // Go to (8).
+  __ b(gt, &not_long_external);  // Go to (7).
 
-  // (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);
   __ ldr(r0, FieldMemOperand(subject, HeapObject::kMapOffset));
   __ ldrb(r0, FieldMemOperand(r0, Map::kInstanceTypeOffset));
@@ -1895,15 +1884,15 @@ void RegExpExecStub::Generate(MacroAssembler* masm) {
   __ sub(subject,
          subject,
          Operand(SeqTwoByteString::kHeaderSize - kHeapObjectTag));
-  __ jmp(&seq_string);    // Go to (5).
+  __ jmp(&seq_string);  // Go to (4).
 
-  // (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);
   __ tst(r1, Operand(kIsNotStringMask | kShortExternalStringMask));
   __ b(ne, &runtime);
 
-  // (9) Sliced string.  Replace subject with parent.  Go to (4).
+  // (8) Sliced string.  Replace subject with parent.  Go to (4).
   // Load offset into r9 and replace subject string with parent.
   __ ldr(r9, FieldMemOperand(subject, SlicedString::kOffsetOffset));
   __ SmiUntag(r9);