MIPS: Porting r10221 to ARM (avoid bailing out to runtime for short substrings).

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 47f24a0ddfcbaa3256e73a072af4d4595a66ce7c..693b1aefb95293334f28104ce6e64cf37c872fb3 100644
--- a/src/mips/code-stubs-mips.cc
+++ b/src/mips/code-stubs-mips.cc
@@ -5972,7 +5972,7 @@ void StringHelper::GenerateHashGetHash(MacroAssembler* masm,
 
 
 void SubStringStub::Generate(MacroAssembler* masm) {
-  Label sub_string_runtime;
+  Label runtime;
   // Stack frame on entry.
   //  ra: return address
   //  sp[0]: to
@@ -5990,53 +5990,35 @@ void SubStringStub::Generate(MacroAssembler* masm) {
   static const int kFromOffset = 1 * kPointerSize;
   static const int kStringOffset = 2 * kPointerSize;
 
-  Register to = t2;
-  Register from = t3;
-
-  // Check bounds and smi-ness.
-  __ lw(to, MemOperand(sp, kToOffset));
-  __ lw(from, MemOperand(sp, kFromOffset));
+  __ lw(a2, MemOperand(sp, kToOffset));
+  __ lw(a3, MemOperand(sp, kFromOffset));
   STATIC_ASSERT(kFromOffset == kToOffset + 4);
   STATIC_ASSERT(kSmiTag == 0);
   STATIC_ASSERT(kSmiTagSize + kSmiShiftSize == 1);
 
-  __ JumpIfNotSmi(from, &sub_string_runtime);
-  __ JumpIfNotSmi(to, &sub_string_runtime);
+  // Utilize delay slots. SmiUntag doesn't emit a jump, everything else is
+  // safe in this case.
+  __ JumpIfSmi(a2, &runtime, at, USE_DELAY_SLOT);
+  __ SmiUntag(a2);
+  __ JumpIfSmi(a3, &runtime, at, USE_DELAY_SLOT);
+  __ SmiUntag(a3);
 
-  __ sra(a3, from, kSmiTagSize);  // Remove smi tag.
-  __ sra(t5, to, kSmiTagSize);  // Remove smi tag.
+  // Both a2 and a3 are untagged integers.
 
-  // a3: from index (untagged smi)
-  // t5: to index (untagged smi)
-
-  __ Branch(&sub_string_runtime, lt, a3, Operand(zero_reg));  // From < 0.
+  __ Branch(&runtime, lt, a3, Operand(zero_reg));  // From < 0.
 
   __ subu(a2, t5, a3);
-  __ Branch(&sub_string_runtime, gt, a3, Operand(t5));  // Fail if from > to.
-
-  // Special handling of sub-strings of length 1 and 2. One character strings
-  // are handled in the runtime system (looked up in the single character
-  // cache). Two character strings are looked for in the symbol cache in
-  // generated code.
-  __ Branch(&sub_string_runtime, lt, a2, Operand(2));
-
-  // Both to and from are smis.
-
-  // a2: result string length
-  // a3: from index (untagged smi)
-  // t2: (a.k.a. to): to (smi)
-  // t3: (a.k.a. from): from offset (smi)
-  // t5: to index (untagged smi)
+  __ Branch(&runtime, gt, a3, Operand(t5));  // Fail if from > to.
 
-  // Make sure first argument is a sequential (or flat) string.
+  // Make sure first argument is a string.
   __ lw(v0, MemOperand(sp, kStringOffset));
-  __ Branch(&sub_string_runtime, eq, v0, Operand(kSmiTagMask));
+  __ Branch(&runtime, eq, v0, Operand(kSmiTagMask));
 
   __ lw(a1, FieldMemOperand(v0, HeapObject::kMapOffset));
   __ lbu(a1, FieldMemOperand(a1, Map::kInstanceTypeOffset));
   __ And(t4, v0, Operand(kIsNotStringMask));
 
-  __ Branch(&sub_string_runtime, ne, t4, Operand(zero_reg));
+  __ Branch(&runtime, ne, t4, Operand(zero_reg));
 
   // Short-cut for the case of trivial substring.
   Label return_v0;
@@ -6046,74 +6028,16 @@ void SubStringStub::Generate(MacroAssembler* masm) {
   __ sra(t0, t0, 1);
   __ Branch(&return_v0, eq, a2, Operand(t0));
 
-  Label create_slice;
-  if (FLAG_string_slices) {
-    __ Branch(&create_slice, ge, a2, Operand(SlicedString::kMinLength));
-  }
-
-  // v0: original string
-  // a1: instance type
-  // a2: result string length
-  // a3: from index (untagged smi)
-  // t2: (a.k.a. to): to (smi)
-  // t3: (a.k.a. from): from offset (smi)
-  // t5: to index (untagged smi)
-
-  Label seq_string;
-  __ And(t0, a1, Operand(kStringRepresentationMask));
-  STATIC_ASSERT(kSeqStringTag < kConsStringTag);
-  STATIC_ASSERT(kConsStringTag < kExternalStringTag);
-  STATIC_ASSERT(kConsStringTag < kSlicedStringTag);
-
-  // Slices and external strings go to runtime.
-  __ Branch(&sub_string_runtime, gt, t0, Operand(kConsStringTag));
-
-  // Sequential strings are handled directly.
-  __ Branch(&seq_string, lt, t0, Operand(kConsStringTag));
-
-  // Cons string. Try to recurse (once) on the first substring.
-  // (This adds a little more generality than necessary to handle flattened
-  // cons strings, but not much).
-  __ lw(v0, FieldMemOperand(v0, ConsString::kFirstOffset));
-  __ lw(t0, FieldMemOperand(v0, HeapObject::kMapOffset));
-  __ lbu(a1, FieldMemOperand(t0, Map::kInstanceTypeOffset));
-  STATIC_ASSERT(kSeqStringTag == 0);
-  // Cons, slices and external strings go to runtime.
-  __ Branch(&sub_string_runtime, ne, a1, Operand(kStringRepresentationMask));
-
-  // Definitly a sequential string.
-  __ bind(&seq_string);
-
-  // v0: original string
-  // a1: instance type
-  // a2: result string length
-  // a3: from index (untagged smi)
-  // t2: (a.k.a. to): to (smi)
-  // t3: (a.k.a. from): from offset (smi)
-  // t5: to index (untagged smi)
-
-  __ lw(t0, FieldMemOperand(v0, String::kLengthOffset));
-  __ Branch(&sub_string_runtime, lt, t0, Operand(to));  // Fail if to > length.
-  to = no_reg;
-
-  // v0: original string or left hand side of the original cons string.
-  // a1: instance type
-  // a2: result string length
-  // a3: from index (untagged smi)
-  // t3: (a.k.a. from): from offset (smi)
-  // t5: to index (untagged smi)
-
-  // Check for flat ASCII string.
-  Label non_ascii_flat;
-  STATIC_ASSERT(kTwoByteStringTag == 0);
-
-  __ And(t4, a1, Operand(kStringEncodingMask));
-  __ Branch(&non_ascii_flat, eq, t4, Operand(zero_reg));
 
   Label result_longer_than_two;
-  __ Branch(&result_longer_than_two, gt, a2, Operand(2));
+  // Check for special case of two character ascii string, in which case
+  // we do a lookup in the symbol table first.
+  __ li(t0, 2);
+  __ Branch(&result_longer_than_two, gt, a2, Operand(t0));
+  __ Branch(&runtime, lt, a2, Operand(t0));
+
+  __ JumpIfInstanceTypeIsNotSequentialAscii(a1, a1, &runtime);
 
-  // Sub string of length 2 requested.
   // Get the two characters forming the sub string.
   __ Addu(v0, v0, Operand(a3));
   __ lbu(a3, FieldMemOperand(v0, SeqAsciiString::kHeaderSize));
@@ -6123,31 +6047,126 @@ void SubStringStub::Generate(MacroAssembler* masm) {
   Label make_two_character_string;
   StringHelper::GenerateTwoCharacterSymbolTableProbe(
       masm, a3, t0, a1, t1, t2, t3, t4, &make_two_character_string);
-  Counters* counters = masm->isolate()->counters();
   __ jmp(&return_v0);
 
   // a2: result string length.
   // a3: two characters combined into halfword in little endian byte order.
   __ bind(&make_two_character_string);
-  __ AllocateAsciiString(v0, a2, t0, t1, t4, &sub_string_runtime);
+  __ AllocateAsciiString(v0, a2, t0, t1, t4, &runtime);
   __ sh(a3, FieldMemOperand(v0, SeqAsciiString::kHeaderSize));
   __ jmp(&return_v0);
 
   __ bind(&result_longer_than_two);
 
-  // Locate 'from' character of string.
-  __ Addu(t1, v0, Operand(SeqAsciiString::kHeaderSize - kHeapObjectTag));
-  __ sra(t4, from, 1);
-  __ Addu(t1, t1, t4);
+  // Deal with different string types: update the index if necessary
+  // and put the underlying string into t1.
+  // v0: original string
+  // a1: instance type
+  // a2: length
+  // a3: from index (untagged)
+  Label underlying_unpacked, sliced_string, seq_or_external_string;
+  // If the string is not indirect, it can only be sequential or external.
+  STATIC_ASSERT(kIsIndirectStringMask == (kSlicedStringTag & kConsStringTag));
+  STATIC_ASSERT(kIsIndirectStringMask != 0);
+  __ And(t0, a1, Operand(kIsIndirectStringMask));
+  __ Branch(USE_DELAY_SLOT, &seq_or_external_string, eq, t0, Operand(zero_reg));
+
+  __ And(t0, a1, Operand(kSlicedNotConsMask));
+  __ Branch(&sliced_string, ne, t0, Operand(zero_reg));
+  // Cons string.  Check whether it is flat, then fetch first part.
+  __ lw(t1, FieldMemOperand(v0, ConsString::kSecondOffset));
+  __ LoadRoot(t0, Heap::kEmptyStringRootIndex);
+  __ Branch(&runtime, ne, t1, Operand(t0));
+  __ lw(t1, FieldMemOperand(v0, ConsString::kFirstOffset));
+  // Update instance type.
+  __ lw(a1, FieldMemOperand(t1, HeapObject::kMapOffset));
+  __ lbu(a1, FieldMemOperand(a1, Map::kInstanceTypeOffset));
+  __ jmp(&underlying_unpacked);
+
+  __ bind(&sliced_string);
+  // Sliced string.  Fetch parent and correct start index by offset.
+  __ lw(t1, FieldMemOperand(v0, SlicedString::kOffsetOffset));
+  __ sra(t1, t1, 1);
+  __ Addu(a3, a3, t1);
+  __ lw(t1, FieldMemOperand(v0, SlicedString::kParentOffset));
+  // Update instance type.
+  __ lw(a1, FieldMemOperand(t1, HeapObject::kMapOffset));
+  __ lbu(a1, FieldMemOperand(a1, Map::kInstanceTypeOffset));
+  __ jmp(&underlying_unpacked);
 
-  // Allocate the result.
-  __ AllocateAsciiString(v0, a2, t4, t0, a1, &sub_string_runtime);
+  __ bind(&seq_or_external_string);
+  // Sequential or external string.  Just move string to the expected register.
+  __ mov(t1, v0);
+
+  __ bind(&underlying_unpacked);
+
+  if (FLAG_string_slices) {
+    Label copy_routine;
+    // t1: underlying subject string
+    // a1: instance type of underlying subject string
+    // a2: length
+    // a3: adjusted start index (untagged)
+    // Short slice.  Copy instead of slicing.
+    __ Branch(&copy_routine, lt, a2, Operand(SlicedString::kMinLength));
+    // Allocate new sliced string.  At this point we do not reload the instance
+    // type including the string encoding because we simply rely on the info
+    // provided by the original string.  It does not matter if the original
+    // string's encoding is wrong because we always have to recheck encoding of
+    // the newly created string's parent anyways due to externalized strings.
+    Label two_byte_slice, set_slice_header;
+    STATIC_ASSERT((kStringEncodingMask & kAsciiStringTag) != 0);
+    STATIC_ASSERT((kStringEncodingMask & kTwoByteStringTag) == 0);
+    __ And(t0, a1, Operand(kStringEncodingMask));
+    __ Branch(&two_byte_slice, eq, t0, Operand(zero_reg));
+    __ AllocateAsciiSlicedString(v0, a2, t2, t3, &runtime);
+    __ jmp(&set_slice_header);
+    __ bind(&two_byte_slice);
+    __ AllocateTwoByteSlicedString(v0, a2, t2, t3, &runtime);
+    __ bind(&set_slice_header);
+    __ sll(a3, a3, 1);
+    __ sw(a3, FieldMemOperand(v0, SlicedString::kOffsetOffset));
+    __ sw(t1, FieldMemOperand(v0, SlicedString::kParentOffset));
+    __ jmp(&return_v0);
+
+    __ bind(&copy_routine);
+  }
+
+  // t1: underlying subject string
+  // a1: instance type of underlying subject string
+  // a2: length
+  // a3: adjusted start index (untagged)
+  Label two_byte_sequential, sequential_string, allocate_result;
+  STATIC_ASSERT(kExternalStringTag != 0);
+  STATIC_ASSERT(kSeqStringTag == 0);
+  __ And(t0, a1, Operand(kExternalStringTag));
+  __ Branch(&sequential_string, eq, t0, Operand(zero_reg));
+
+  // Handle external string.
+  // Rule out short external strings.
+  STATIC_CHECK(kShortExternalStringTag != 0);
+  __ And(t0, a1, Operand(kShortExternalStringTag));
+  __ Branch(&runtime, ne, t0, Operand(zero_reg));
+  __ lw(t1, FieldMemOperand(t1, ExternalString::kResourceDataOffset));
+  // t1 already points to the first character of underlying string.
+  __ jmp(&allocate_result);
+
+  __ bind(&sequential_string);
+  // Locate first character of underlying subject string.
+  STATIC_ASSERT(SeqTwoByteString::kHeaderSize == SeqAsciiString::kHeaderSize);
+  __ Addu(t1, t1, Operand(SeqAsciiString::kHeaderSize - kHeapObjectTag));
+
+  __ bind(&allocate_result);
+  // Sequential acii string.  Allocate the result.
+  STATIC_ASSERT((kAsciiStringTag & kStringEncodingMask) != 0);
+  __ And(t0, a1, Operand(kStringEncodingMask));
+  __ Branch(&two_byte_sequential, eq, t0, Operand(zero_reg));
+
+  // Allocate and copy the resulting ascii string.
+  __ AllocateAsciiString(v0, a2, t0, t2, t3, &runtime);
+
+  // Locate first character of substring to copy.
+  __ Addu(t1, t1, a3);
 
-  // v0: result string
-  // a2: result string length
-  // a3: from index (untagged smi)
-  // t1: first character of substring to copy
-  // t3: (a.k.a. from): from offset (smi)
   // Locate first character of result.
   __ Addu(a1, v0, Operand(SeqAsciiString::kHeaderSize - kHeapObjectTag));
 
@@ -6160,30 +6179,17 @@ void SubStringStub::Generate(MacroAssembler* masm) {
       masm, a1, t1, a2, a3, t0, t2, t3, t4, COPY_ASCII | DEST_ALWAYS_ALIGNED);
   __ jmp(&return_v0);
 
-  __ bind(&non_ascii_flat);
-  // a2: result string length
-  // t1: string
-  // t3: (a.k.a. from): from offset (smi)
-  // Check for flat two byte string.
-
-  // Locate 'from' character of string.
-  __ Addu(t1, v0, Operand(SeqTwoByteString::kHeaderSize - kHeapObjectTag));
-  // As "from" is a smi it is 2 times the value which matches the size of a two
-  // byte character.
-  STATIC_ASSERT(kSmiTagSize == 1 && kSmiTag == 0);
-  __ Addu(t1, t1, Operand(from));
-
-  // Allocate the result.
-  __ AllocateTwoByteString(v0, a2, a1, a3, t0, &sub_string_runtime);
+  // Allocate and copy the resulting two-byte string.
+  __ bind(&two_byte_sequential);
+  __ AllocateTwoByteString(v0, a2, t0, t2, t3, &runtime);
 
-  // v0: result string
-  // a2: result string length
-  // t1: first character of substring to copy
+  // Locate first character of substring to copy.
+  STATIC_ASSERT(kSmiTagSize == 1 && kSmiTag == 0);
+  __ sll(t0, a3, 1);
+  __ Addu(t1, t1, t0);
   // Locate first character of result.
   __ Addu(a1, v0, Operand(SeqTwoByteString::kHeaderSize - kHeapObjectTag));
 
-  from = no_reg;
-
   // v0: result string.
   // a1: first character of result.
   // a2: result length.
@@ -6191,75 +6197,14 @@ void SubStringStub::Generate(MacroAssembler* masm) {
   STATIC_ASSERT((SeqTwoByteString::kHeaderSize & kObjectAlignmentMask) == 0);
   StringHelper::GenerateCopyCharactersLong(
       masm, a1, t1, a2, a3, t0, t2, t3, t4, DEST_ALWAYS_ALIGNED);
-  __ jmp(&return_v0);
-
-  if (FLAG_string_slices) {
-    __ bind(&create_slice);
-    // v0: original string
-    // a1: instance type
-    // a2: length
-    // a3: from index (untagged smi)
-    // t2 (a.k.a. to): to (smi)
-    // t3 (a.k.a. from): from offset (smi)
-    Label allocate_slice, sliced_string, seq_or_external_string;
-    // If the string is not indirect, it can only be sequential or external.
-    STATIC_ASSERT(kIsIndirectStringMask == (kSlicedStringTag & kConsStringTag));
-    STATIC_ASSERT(kIsIndirectStringMask != 0);
-    __ And(t4, a1, Operand(kIsIndirectStringMask));
-    // External string.  Jump to runtime.
-    __ Branch(&seq_or_external_string, eq, t4, Operand(zero_reg));
-
-    __ And(t4, a1, Operand(kSlicedNotConsMask));
-    __ Branch(&sliced_string, ne, t4, Operand(zero_reg));
-    // Cons string.  Check whether it is flat, then fetch first part.
-    __ lw(t1, FieldMemOperand(v0, ConsString::kSecondOffset));
-    __ LoadRoot(t5, Heap::kEmptyStringRootIndex);
-    __ Branch(&sub_string_runtime, ne, t1, Operand(t5));
-    __ lw(t1, FieldMemOperand(v0, ConsString::kFirstOffset));
-    __ jmp(&allocate_slice);
-
-    __ bind(&sliced_string);
-    // Sliced string.  Fetch parent and correct start index by offset.
-    __ lw(t1, FieldMemOperand(v0, SlicedString::kOffsetOffset));
-    __ addu(t3, t3, t1);
-    __ lw(t1, FieldMemOperand(v0, SlicedString::kParentOffset));
-    __ jmp(&allocate_slice);
-
-    __ bind(&seq_or_external_string);
-    // Sequential or external string.  Just move string to the correct register.
-    __ mov(t1, v0);
-
-    __ bind(&allocate_slice);
-    // a1: instance type of original string
-    // a2: length
-    // t1: underlying subject string
-    // t3 (a.k.a. from): from offset (smi)
-    // Allocate new sliced string.  At this point we do not reload the instance
-    // type including the string encoding because we simply rely on the info
-    // provided by the original string.  It does not matter if the original
-    // string's encoding is wrong because we always have to recheck encoding of
-    // the newly created string's parent anyways due to externalized strings.
-    Label two_byte_slice, set_slice_header;
-    STATIC_ASSERT((kStringEncodingMask & kAsciiStringTag) != 0);
-    STATIC_ASSERT((kStringEncodingMask & kTwoByteStringTag) == 0);
-    __ And(t4, a1, Operand(kStringEncodingMask));
-    __ Branch(&two_byte_slice, eq, t4, Operand(zero_reg));
-    __ AllocateAsciiSlicedString(v0, a2, a3, t0, &sub_string_runtime);
-    __ jmp(&set_slice_header);
-    __ bind(&two_byte_slice);
-    __ AllocateTwoByteSlicedString(v0, a2, a3, t0, &sub_string_runtime);
-    __ bind(&set_slice_header);
-    __ sw(t3, FieldMemOperand(v0, SlicedString::kOffsetOffset));
-    __ sw(t1, FieldMemOperand(v0, SlicedString::kParentOffset));
-  }
 
   __ bind(&return_v0);
+  Counters* counters = masm->isolate()->counters();
   __ IncrementCounter(counters->sub_string_native(), 1, a3, t0);
-  __ Addu(sp, sp, Operand(3 * kPointerSize));
-  __ Ret();
+  __ DropAndRet(3);
 
   // Just jump to runtime to create the sub string.
-  __ bind(&sub_string_runtime);
+  __ bind(&runtime);
   __ TailCallRuntime(Runtime::kSubString, 3, 1);
 }