Create specialized code stubs for PixelArray loads.

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 0a1ffbda5ff4e683fde565b9fd3d4f6540fddb74..259b4bf8e1ee1050cae96c838a727774454eabfd 100644
--- a/src/arm/code-stubs-arm.cc
+++ b/src/arm/code-stubs-arm.cc
@@ -5718,6 +5718,66 @@ void ICCompareStub::GenerateMiss(MacroAssembler* masm) {
 }
 
 

[Søren Thygesen Gjesse, 2011/02/01 12:02:56]

Please add a comment and mention how the different exit lables work (maybe in
the .h file).

[danno, 2011/02/03 12:53:26]

Done.

+void GenerateFastPixelArrayLoad(MacroAssembler* masm,
+                                Register receiver,
+                                Register key,
+                                Register elements_map,
+                                Register elements,
+                                Register scratch1,
+                                Register scratch2,
+                                Register result,
+                                Label* not_pixel_array,
+                                Label* key_not_smi,
+                                Label* out_of_range) {
+  // Register use:
+  //
+  // receiver - holds the receiver on entry.
+  //            Unchanged unless 'result' is the same register.
+  //
+  // key      - holds the smi key on entry.
+  //            Unchanged unless 'result' is the same register.
+  //
+  // elements - set to be the receiver's elements on exit.
+  //
+  // elements_map - set to be the map of the receiver's elements
+  //            on exit.
+  //
+  // result   - holds the result of the pixel array load on exit,
+  //            tagged as a smi if successful.
+  //
+  // Scratch registers:
+  //
+  // scratch1 - holds the receiver's elements, the length of the
+  //            pixel array, the pointer to external elements and
+  //            the untagged result.
+  //
+  // scratch2 - holds the untaged key.
+
+  // Verify that the receiver has pixel array elements.
+  __ ldr(elements, FieldMemOperand(receiver, JSObject::kElementsOffset));
+  __ LoadRoot(scratch1, Heap::kPixelArrayMapRootIndex);

[Mads Ager (chromium), 2011/02/01 12:02:12]

Can you use __ CheckMap() that accepts a root array index?

[danno, 2011/02/03 12:53:26]

Done.

+  __ ldr(elements_map, FieldMemOperand(elements, JSObject::kMapOffset));
+  __ cmp(elements_map, scratch1);
+  __ b(ne, not_pixel_array);
+
+  // Key must be a smi that is in the range of the pixel array.
+  if (key_not_smi != NULL) {

[Søren Thygesen Gjesse, 2011/02/01 12:02:56]

Please explain the if here. If key_not_smi is NULL key needs to have been smi
checked already - right? And if that is the case please add else part

} else {
  if (FLAG_debug_code) {
    __ ABortIfNotSmi(key);
  }
}

[danno, 2011/02/03 12:53:26]

Done.

+    __ JumpIfNotSmi(key, key_not_smi);
+  }
+  __ ldr(scratch1, FieldMemOperand(elements, PixelArray::kLengthOffset));
+  __ SmiUntag(scratch2, key);
+  __ cmp(scratch2, scratch1);
+  __ b(hs, out_of_range);

[Søren Thygesen Gjesse, 2011/02/01 12:02:56]

Maybe comment that the unsigned check covers negative keys.

[danno, 2011/02/03 12:53:26]

Done.

+
+  // Perform the indexed load and tag the result as a smi.
+  __ ldr(scratch1,
+         FieldMemOperand(elements, PixelArray::kExternalPointerOffset));
+  __ ldrb(scratch1, MemOperand(scratch1, scratch2));
+  __ SmiTag(r0, scratch1);
+  __ Ret();
+}
+
+
 #undef __
 
 } }  // namespace v8::internal