Some assembler-level optimizations on ARM.

src/arm/codegen-arm.cc

Index: src/arm/codegen-arm.cc
diff --git a/src/arm/codegen-arm.cc b/src/arm/codegen-arm.cc
index 3371e8a6b1dddeabf991a81076f545d96c39aba0..102de820d45cb0ce4be7754bb6ecb27ec8dadf4b 100644
--- a/src/arm/codegen-arm.cc
+++ b/src/arm/codegen-arm.cc
@@ -104,10 +104,10 @@ void ElementsTransitionGenerator::GenerateSmiOnlyToDouble(
   __ add(lr, lr, Operand(r5, LSL, 2));
   __ AllocateInNewSpace(lr, r6, r7, r9, &gc_required, NO_ALLOCATION_FLAGS);
   // r6: destination FixedDoubleArray, not tagged as heap object
+  // Set destination FixedDoubleArray's length and map.
   __ LoadRoot(r9, Heap::kFixedDoubleArrayMapRootIndex);
-  __ str(r9, MemOperand(r6, HeapObject::kMapOffset));
-  // Set destination FixedDoubleArray's length.
   __ str(r5, MemOperand(r6, FixedDoubleArray::kLengthOffset));
+  __ str(r9, MemOperand(r6, HeapObject::kMapOffset));
   // Update receiver's map.
 
   __ str(r3, FieldMemOperand(r2, HeapObject::kMapOffset));
@@ -155,10 +155,11 @@ void ElementsTransitionGenerator::GenerateSmiOnlyToDouble(
   __ bind(&loop);
   __ ldr(r9, MemOperand(r3, 4, PostIndex));
   // r9: current element
-  __ JumpIfNotSmi(r9, &convert_hole);
+  STATIC_ASSERT(kSmiTagSize == 1 && kSmiTag == 0);

[ulan, 2012/01/27 13:19:11]

Can we introduce UntagAndJumpIfNotSmi for these tree lines?

+  __ mov(r9, Operand(r9, ASR, kSmiShiftSize), SetCC);
+  __ b(cs, &convert_hole);  // Non-smi sets shifter carry.
 
   // Normal smi, convert to double and store.
-  __ SmiUntag(r9);
   if (vfp3_supported) {
     CpuFeatures::Scope scope(VFP3);
     __ vmov(s0, r9);
@@ -181,6 +182,9 @@ void ElementsTransitionGenerator::GenerateSmiOnlyToDouble(
   // Hole found, store the-hole NaN.
   __ bind(&convert_hole);
   if (FLAG_debug_code) {
+    // Restore a "smi-untagged" heap object.
+    __ SmiTag(r9);
+    __ orr(r9, r9, Operand(1));
     __ CompareRoot(r9, Heap::kTheHoleValueRootIndex);
     __ Assert(eq, "object found in smi-only array");
   }
@@ -208,9 +212,8 @@ void ElementsTransitionGenerator::GenerateDoubleToObject(
   Label entry, loop, convert_hole, gc_required;
 
   __ push(lr);
-  __ Push(r3, r2, r1, r0);
-
   __ ldr(r4, FieldMemOperand(r2, JSObject::kElementsOffset));
+  __ Push(r3, r2, r1, r0);
   __ ldr(r5, FieldMemOperand(r4, FixedArray::kLengthOffset));
   // r4: source FixedDoubleArray
   // r5: number of elements (smi-tagged)
@@ -220,10 +223,10 @@ void ElementsTransitionGenerator::GenerateDoubleToObject(
   __ add(r0, r0, Operand(r5, LSL, 1));
   __ AllocateInNewSpace(r0, r6, r7, r9, &gc_required, NO_ALLOCATION_FLAGS);
   // r6: destination FixedArray, not tagged as heap object
+  // Set destination FixedDoubleArray's length and map.
   __ LoadRoot(r9, Heap::kFixedArrayMapRootIndex);
-  __ str(r9, MemOperand(r6, HeapObject::kMapOffset));
-  // Set destination FixedDoubleArray's length.
   __ str(r5, MemOperand(r6, FixedDoubleArray::kLengthOffset));
+  __ str(r9, MemOperand(r6, HeapObject::kMapOffset));
 
   // Prepare for conversion loop.
   __ add(r4, r4, Operand(FixedDoubleArray::kHeaderSize - kHeapObjectTag + 4));
@@ -325,8 +328,8 @@ void StringCharLoadGenerator::Generate(MacroAssembler* masm,
   // Handle slices.
   Label indirect_string_loaded;
   __ ldr(result, FieldMemOperand(string, SlicedString::kOffsetOffset));
-  __ add(index, index, Operand(result, ASR, kSmiTagSize));
   __ ldr(string, FieldMemOperand(string, SlicedString::kParentOffset));
+  __ add(index, index, Operand(result, ASR, kSmiTagSize));
   __ jmp(&indirect_string_loaded);
 
   // Handle cons strings.
@@ -336,10 +339,9 @@ void StringCharLoadGenerator::Generate(MacroAssembler* masm,
   // the string.
   __ bind(&cons_string);
   __ ldr(result, FieldMemOperand(string, ConsString::kSecondOffset));
-  __ LoadRoot(ip, Heap::kEmptyStringRootIndex);
-  __ cmp(result, ip);
-  __ b(ne, call_runtime);
+  __ CompareRoot(result, Heap::kEmptyStringRootIndex);
   // Get the first of the two strings and load its instance type.
+  __ b(ne, call_runtime);  // This branch refers to the previous CompareRoot.

[ulan, 2012/01/27 13:19:11]

This branch should be above the comment in line 343.

   __ ldr(string, FieldMemOperand(string, ConsString::kFirstOffset));
 
   __ bind(&indirect_string_loaded);