Array index computation dehoisting.

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index 79b56fc077bc930918cc4b3230b31a462c534935..b838b42b3e6a20cdbbfefbbf6251f1b11fa44607 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -2748,7 +2748,11 @@ void LCodeGen::DoLoadKeyedFastElement(LLoadKeyedFastElement* instr) {
 
   // Load the result.
   __ add(scratch, elements, Operand(key, LSL, kPointerSizeLog2));
-  __ ldr(result, FieldMemOperand(scratch, FixedArray::kHeaderSize));
+  __ ldr(result,

[Jakob Kummerow, 2012/05/15 15:53:23]

Formatting proposal:

  uint32_t offset = FixedArray::kHeaderSize +
                    (instr->additional_index() << kPointerSizeLog2);
  __ ldr(result, FieldMemOperand(scratch, offset));

+         FieldMemOperand(scratch,
+                         FixedArray::kHeaderSize
+                             + (instr->additional_index()
+                                 << kPointerSizeLog2)));
 
   // Check for the hole value.
   if (instr->hydrogen()->RequiresHoleCheck()) {
@@ -2780,13 +2784,14 @@ void LCodeGen::DoLoadKeyedFastDoubleElement(
   }
 
   Operand operand = key_is_constant
-      ? Operand(constant_key * (1 << shift_size) +
+      ? Operand(((constant_key + instr->additional_index()) << shift_size) +
                 FixedDoubleArray::kHeaderSize - kHeapObjectTag)
       : Operand(key, LSL, shift_size);
   __ add(elements, elements, operand);
   if (!key_is_constant) {
     __ add(elements, elements,
-           Operand(FixedDoubleArray::kHeaderSize - kHeapObjectTag));
+           Operand((FixedDoubleArray::kHeaderSize - kHeapObjectTag)
+                   + (instr->additional_index() << shift_size)));

[Jakob Kummerow, 2012/05/15 15:53:23]

nit: for consistency, the operator goes at the end of the last line.

   }
 
   __ ldr(scratch, MemOperand(elements, sizeof(kHoleNanLower32)));
@@ -2813,6 +2818,7 @@ void LCodeGen::DoLoadKeyedSpecializedArrayElement(
     key = ToRegister(instr->key());
   }
   int shift_size = ElementsKindToShiftSize(elements_kind);
+  int additional_offset = instr->additional_index() << shift_size;
 
   if (elements_kind == EXTERNAL_FLOAT_ELEMENTS ||
       elements_kind == EXTERNAL_DOUBLE_ELEMENTS) {
@@ -2823,16 +2829,22 @@ void LCodeGen::DoLoadKeyedSpecializedArrayElement(
         : Operand(key, LSL, shift_size);
     __ add(scratch0(), external_pointer, operand);
     if (elements_kind == EXTERNAL_FLOAT_ELEMENTS) {
-      __ vldr(result.low(), scratch0(), 0);
+      __ vldr(result.low(), scratch0(), additional_offset);
       __ vcvt_f64_f32(result, result.low());
     } else  {  // i.e. elements_kind == EXTERNAL_DOUBLE_ELEMENTS
-      __ vldr(result, scratch0(), 0);
+      __ vldr(result, scratch0(), additional_offset);
     }
   } else {
     Register result = ToRegister(instr->result());
+    if (instr->additional_index() != 0 && !key_is_constant) {
+      __ add(scratch0(), key, Operand(instr->additional_index()));
+    }
     MemOperand mem_operand(key_is_constant
-        ? MemOperand(external_pointer, constant_key * (1 << shift_size))
-        : MemOperand(external_pointer, key, LSL, shift_size));
+        ? MemOperand(external_pointer,
+                     constant_key * (1 << shift_size) + additional_offset)

[Jakob Kummerow, 2012/05/15 15:53:23]

nit: drop the "* (1". Just "(constant_key << shift_size)". It's cleaner.

+        : (instr->additional_index() == 0
+           ? MemOperand(external_pointer, key, LSL, shift_size)
+           : MemOperand(external_pointer, scratch0(), LSL, shift_size)));
     switch (elements_kind) {
       case EXTERNAL_BYTE_ELEMENTS:
         __ ldrsb(result, mem_operand);
@@ -3730,10 +3742,16 @@ void LCodeGen::DoStoreKeyedFastElement(LStoreKeyedFastElement* instr) {
     ASSERT(!instr->hydrogen()->NeedsWriteBarrier());
     LConstantOperand* const_operand = LConstantOperand::cast(instr->key());
     int offset =
-        ToInteger32(const_operand) * kPointerSize + FixedArray::kHeaderSize;
+        (ToInteger32(const_operand) + instr->additional_index())
+        * kPointerSize + FixedArray::kHeaderSize;

[Jakob Kummerow, 2012/05/15 15:53:23]

nit: looks like "* kPointerSize" might just fit onto the line before, which
would make more sense.

     __ str(value, FieldMemOperand(elements, offset));
   } else {
     __ add(scratch, elements, Operand(key, LSL, kPointerSizeLog2));
+    if (instr->additional_index() != 0) {
+      __ add(scratch,
+             scratch,
+             Operand(instr->additional_index() << kPointerSizeLog2));
+    }
     __ str(value, FieldMemOperand(scratch, FixedArray::kHeaderSize));
   }
 
@@ -3793,7 +3811,7 @@ void LCodeGen::DoStoreKeyedFastDoubleElement(
             vs);
   }
 
-  __ vstr(value, scratch, 0);
+  __ vstr(value, scratch, instr->additional_index() << shift_size);
 }
 
 
@@ -3814,6 +3832,7 @@ void LCodeGen::DoStoreKeyedSpecializedArrayElement(
     key = ToRegister(instr->key());
   }
   int shift_size = ElementsKindToShiftSize(elements_kind);
+  int additional_offset = instr->additional_index() << shift_size;
 
   if (elements_kind == EXTERNAL_FLOAT_ELEMENTS ||
       elements_kind == EXTERNAL_DOUBLE_ELEMENTS) {
@@ -3824,15 +3843,22 @@ void LCodeGen::DoStoreKeyedSpecializedArrayElement(
     __ add(scratch0(), external_pointer, operand);
     if (elements_kind == EXTERNAL_FLOAT_ELEMENTS) {
       __ vcvt_f32_f64(double_scratch0().low(), value);
-      __ vstr(double_scratch0().low(), scratch0(), 0);
+      __ vstr(double_scratch0().low(), scratch0(), additional_offset);
     } else {  // i.e. elements_kind == EXTERNAL_DOUBLE_ELEMENTS
-      __ vstr(value, scratch0(), 0);
+      __ vstr(value, scratch0(), additional_offset);
     }
   } else {
     Register value(ToRegister(instr->value()));
+    if (instr->additional_index() != 0 && !key_is_constant) {
+      __ add(scratch0(), key, Operand(instr->additional_index()));
+    }
     MemOperand mem_operand(key_is_constant
-        ? MemOperand(external_pointer, constant_key * (1 << shift_size))
-        : MemOperand(external_pointer, key, LSL, shift_size));
+        ? MemOperand(external_pointer,
+                     (constant_key + instr->additional_index())
+                         * (1 << shift_size))
+        : (instr->additional_index() == 0
+           ? MemOperand(external_pointer, key, LSL, shift_size)

[Jakob Kummerow, 2012/05/15 15:53:23]

nit: 4 space indent please.

+           : MemOperand(external_pointer, scratch0(), LSL, shift_size)));
     switch (elements_kind) {
       case EXTERNAL_PIXEL_ELEMENTS:
       case EXTERNAL_BYTE_ELEMENTS: