Generated code for substring slices in ia32.

src/ia32/code-stubs-ia32.cc

Index: src/ia32/code-stubs-ia32.cc
diff --git a/src/ia32/code-stubs-ia32.cc b/src/ia32/code-stubs-ia32.cc
index d76e4bf1f444a40f4021827d747738cd21bd7d53..1b3acc237636d14d793615728747f08860a69879 100644
--- a/src/ia32/code-stubs-ia32.cc
+++ b/src/ia32/code-stubs-ia32.cc
@@ -5642,9 +5642,6 @@ void StringHelper::GenerateHashGetHash(MacroAssembler* masm,
 void SubStringStub::Generate(MacroAssembler* masm) {
   Label runtime;
 
-  if (FLAG_string_slices) {
-    __ jmp(&runtime);
-  }
   // Stack frame on entry.
   //  esp[0]: return address
   //  esp[4]: to
@@ -5706,7 +5703,83 @@ void SubStringStub::Generate(MacroAssembler* masm) {
   __ movzx_b(ebx, FieldOperand(ebx, Map::kInstanceTypeOffset));
   __ Set(ecx, Immediate(2));
 
-  __ bind(&result_longer_than_two);
+  if (FLAG_string_slices) {
+    Label copy_rountine;
+    // If coming from the make_two_character_string path, the string
+    // is too short to be sliced anyways.
+    STATIC_ASSERT(2 < SlicedString::kMinLength);
+    __ jmp(&copy_routine);
+    __ bind(&result_longer_than_two);
+
+    // eax: string
+    // ebx: instance type
+    // ecx: sub string length
+    // edx: from index (smi)
+   Label allocate_slice, sliced_string, seq_string;
+    __ cmp(ecx, SlicedString::kMinLength);
+    // Short slice.  Copy instead of slicing.
+    __ j(less, &copy_routine);
+    STATIC_ASSERT(kSeqStringTag == 0);
+    __ test(ebx, Immediate(kStringRepresentationMask));
+    __ j(zero, &seq_string, Label::kNear);
+    STATIC_ASSERT(kIsIndirectStringMask == (kSlicedStringTag & kConsStringTag));

[antonm, 2011/08/29 17:19:26]

may those go too?

+    STATIC_ASSERT(kIsIndirectStringMask != 0);
+    __ test(ebx, Immediate(kIsIndirectStringMask));
+    // External string.  Jump to runtime.
+    __ j(zero, &runtime);
+
+    Factory* factory = masm->isolate()->factory();
+    __ test(ebx, Immediate(kSlicedNotConsMask));
+    __ j(not_zero, &sliced_string, Label::kNear);
+    // Cons string.  Check whether it is flat, then fetch first part.
+    __ cmp(FieldOperand(eax, ConsString::kSecondOffset),
+           factory->empty_string());
+    __ j(not_equal, &runtime);
+    __ mov(edi, FieldOperand(eax, ConsString::kFirstOffset));
+    __ jmp(&allocate_slice, Label::kNear);
+
+    __ bind(&sliced_string);
+    // Sliced string.  Fetch parent and correct start index by offset.
+    __ add(edx, FieldOperand(eax, SlicedString::kOffsetOffset));
+    __ mov(edi, FieldOperand(eax, SlicedString::kParentOffset));
+    __ jmp(&allocate_slice, Label::kNear);
+
+    __ bind(&seq_string);
+    // Sequential string.  Just move string to the right register.
+    __ mov(edi, eax);
+
+    __ bind(&allocate_slice);
+    // edi: underlying subject string
+    // ebx: instance type of original subject string
+    // edx: offset
+    // ecx: length
+    // Allocate new sliced string.  At this point we do not reload the instance

[Vitaly Repeshko, 2011/08/30 01:17:48]

This is clever, but the comment is a bit confusing. I'd replace "parent" with
"original" to match the comment about ebx. Also later it may help to use "newly
created slice" to avoid confusion with the one we might have just unwrapped.

+    // type including the string encoding because we simply rely on the info
+    // provided by the parent string.  It does not matter if the parent's
+    // encoding is wrong because we always have to recheck encoding of the
+    // slice's parent anyways due to externalized strings.
+    Label two_byte_slice, set_slice_header;
+    STATIC_ASSERT(kAsciiStringTag != 0);
+    __ test(ebx, Immediate(kAsciiStringTag));
+    __ j(zero, &two_byte_slice, Label::kNear);
+    __ AllocateAsciiSlicedString(eax, ebx, no_reg, &runtime);
+    __ jmp(&set_slice_header, Label::kNear);
+    __ bind(&two_byte_slice);
+    __ AllocateSlicedString(eax, ebx, no_reg, &runtime);
+    __ bind(&set_slice_header);
+    __ mov(FieldOperand(eax, SlicedString::kOffsetOffset), edx);
+    __ SmiTag(ecx);
+    __ mov(FieldOperand(eax, SlicedString::kLengthOffset), ecx);
+    __ mov(FieldOperand(eax, SlicedString::kParentOffset), edi);
+    __ mov(FieldOperand(eax, SlicedString::kHashFieldOffset),
+           Immediate(String::kEmptyHashField));
+    __ jmp(&return_eax);
+
+    __ bind(&copy_routine);
+  } else {
+    __ bind(&result_longer_than_two);
+  }
+
   // eax: string
   // ebx: instance type
   // ecx: result string length