[v8-dev] Change generated code for substring not to bail out to runtime system. (issue 8513016)

Wed, 16 Nov 2011 09:26:16 -0800 

Reviewers: Rico,

Message:
I should have kept the behavior in the runtime and that of the generated code in 
sync back when I first implemented this. Please take a look.

Description:
Change generated code for substring not to bail out to runtime system.
There is no need to bail out to runtime system when creating sliced strings of 
external strings since the string content is unimportant.


Please review this at http://codereview.chromium.org/8513016/

SVN Base: https://v8.googlecode.com/svn/branches/bleeding_edge

Affected files:
  M src/arm/code-stubs-arm.cc
  M src/ia32/code-stubs-ia32.cc
  M src/x64/code-stubs-x64.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 b37855b8e0929af23380bce6da69c736fd054954..155f64a97ea41ffed4a55ce373d245823e07ef12 100644 
--- a/src/arm/code-stubs-arm.cc
+++ b/src/arm/code-stubs-arm.cc
@@ -5815,15 +5815,11 @@ void SubStringStub::Generate(MacroAssembler* masm) {
     // r3: from index (untagged smi)
     // r6 (a.k.a. to): to (smi)
     // r7 (a.k.a. from): from offset (smi)
-    Label allocate_slice, sliced_string, seq_string;
-    STATIC_ASSERT(kSeqStringTag == 0);
-    __ tst(r1, Operand(kStringRepresentationMask));
-    __ b(eq, &seq_string);
+    Label allocate_slice, sliced_string, seq_or_external_string;
STATIC_ASSERT(kIsIndirectStringMask == (kSlicedStringTag & kConsStringTag)); 
     STATIC_ASSERT(kIsIndirectStringMask != 0);
     __ tst(r1, Operand(kIsIndirectStringMask));
-    // External string.  Jump to runtime.
-    __ b(eq, &runtime);
+    __ b(eq, &seq_or_external_string);

     __ tst(r1, Operand(kSlicedNotConsMask));
     __ b(ne, &sliced_string);
@@ -5842,8 +5838,8 @@ void SubStringStub::Generate(MacroAssembler* masm) {
     __ ldr(r5, FieldMemOperand(r0, SlicedString::kParentOffset));
     __ jmp(&allocate_slice);

-    __ bind(&seq_string);
-    // Sequential string.  Just move string to the right register.
+    __ bind(&seq_or_external_string);
+ // Sequential or external string. Just move string to the correct register. 
     __ mov(r5, r0);

     __ bind(&allocate_slice);
Index: src/ia32/code-stubs-ia32.cc
diff --git a/src/ia32/code-stubs-ia32.cc b/src/ia32/code-stubs-ia32.cc
index 23bea4f8568ce2cebeccf8212be82343e75e4d29..e5b25518c14c56b4d5b4fa548a406bd962607664 100644 
--- a/src/ia32/code-stubs-ia32.cc
+++ b/src/ia32/code-stubs-ia32.cc
@@ -5973,18 +5973,14 @@ void SubStringStub::Generate(MacroAssembler* masm) {
     // ebx: instance type
     // ecx: sub string length
     // edx: from index (smi)
-    Label allocate_slice, sliced_string, seq_string;
+    Label allocate_slice, sliced_string, seq_or_external_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)); 
     STATIC_ASSERT(kIsIndirectStringMask != 0);
     __ test(ebx, Immediate(kIsIndirectStringMask));
-    // External string.  Jump to runtime.
-    __ j(zero, &runtime);
+    __ j(zero, &seq_or_external_string, Label::kNear);

     Factory* factory = masm->isolate()->factory();
     __ test(ebx, Immediate(kSlicedNotConsMask));
@@ -6002,8 +5998,8 @@ void SubStringStub::Generate(MacroAssembler* masm) {
     __ mov(edi, FieldOperand(eax, SlicedString::kParentOffset));
     __ jmp(&allocate_slice, Label::kNear);

-    __ bind(&seq_string);
-    // Sequential string.  Just move string to the right register.
+    __ bind(&seq_or_external_string);
+ // Sequential or external string. Just move string to the correct register. 
     __ mov(edi, eax);

     __ bind(&allocate_slice);
Index: src/x64/code-stubs-x64.cc
diff --git a/src/x64/code-stubs-x64.cc b/src/x64/code-stubs-x64.cc
index bf50869ed90f1a381160756ecacbd633c456a1b2..30287e2f17180dccfa09bc82c94028196cccc587 100644 
--- a/src/x64/code-stubs-x64.cc
+++ b/src/x64/code-stubs-x64.cc
@@ -4912,18 +4912,14 @@ void SubStringStub::Generate(MacroAssembler* masm) {
     // rbx: instance type
     // rcx: sub string length
     // rdx: from index (smi)
-    Label allocate_slice, sliced_string, seq_string;
+    Label allocate_slice, sliced_string, seq_or_external_string;
     __ cmpq(rcx, Immediate(SlicedString::kMinLength));
     // Short slice.  Copy instead of slicing.
     __ j(less, &copy_routine);
-    STATIC_ASSERT(kSeqStringTag == 0);
-    __ testb(rbx, Immediate(kStringRepresentationMask));
-    __ j(zero, &seq_string, Label::kNear);
STATIC_ASSERT(kIsIndirectStringMask == (kSlicedStringTag & kConsStringTag)); 
     STATIC_ASSERT(kIsIndirectStringMask != 0);
     __ testb(rbx, Immediate(kIsIndirectStringMask));
-    // External string.  Jump to runtime.
-    __ j(zero, &runtime);
+    __ j(zero, &seq_or_external_string, Label::kNear);

     __ testb(rbx, Immediate(kSlicedNotConsMask));
     __ j(not_zero, &sliced_string, Label::kNear);
@@ -4940,8 +4936,8 @@ void SubStringStub::Generate(MacroAssembler* masm) {
     __ movq(rdi, FieldOperand(rax, SlicedString::kParentOffset));
     __ jmp(&allocate_slice, Label::kNear);

-    __ bind(&seq_string);
-    // Sequential string.  Just move string to the right register.
+    __ bind(&seq_or_external_string);
+ // Sequential or external string. Just move string to the correct register. 
     __ movq(rdi, rax);

     __ bind(&allocate_slice);


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