ARM: Small copy optimization. Copying 64bits at a time.

src/arm/macro-assembler-arm.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 3142 matching lines @@
                                                  Label* gc_required) {
   AllocateHeapNumber(result, scratch1, scratch2, heap_number_map, gc_required);
   sub(scratch1, result, Operand(kHeapObjectTag));
   vstr(value, scratch1, HeapNumber::kValueOffset);
 }
 
 
 // Copies a fixed number of fields of heap objects from src to dst.
 void MacroAssembler::CopyFields(Register dst,
                                 Register src,
-                                RegList temps,
+                                DwVfpRegister double_scratch,
+                                SwVfpRegister single_scratch,

[ulan, 2013/04/12 14:07:04]

Can we implicitly use double_scratch.low() for single_scratch instead passing it
in parameters?

[Rodolph Perfetta, 2013/04/12 14:42:59]

not all double registers have a low (or high), only d0-d15 have them.

[ulan, 2013/04/15 07:44:06]

I see, thanks for clarification!

                                 int field_count) {
-  // At least one bit set in the first 15 registers.
-  ASSERT((temps & ((1 << 15) - 1)) != 0);
-  ASSERT((temps & dst.bit()) == 0);
-  ASSERT((temps & src.bit()) == 0);
-  // Primitive implementation using only one temporary register.
-
-  Register tmp = no_reg;
-  // Find a temp register in temps list.
-  for (int i = 0; i < 15; i++) {
-    if ((temps & (1 << i)) != 0) {
-      tmp.set_code(i);
-      break;
-    }
+  int double_count = field_count / (DwVfpRegister::kSizeInBytes / kPointerSize);
+  for (int i = 0; i < double_count; i++) {
+    vldr(double_scratch, FieldMemOperand(src, i * DwVfpRegister::kSizeInBytes));
+    vstr(double_scratch, FieldMemOperand(dst, i * DwVfpRegister::kSizeInBytes));
   }
-  ASSERT(!tmp.is(no_reg));
-
-  for (int i = 0; i < field_count; i++) {
-    ldr(tmp, FieldMemOperand(src, i * kPointerSize));
-    str(tmp, FieldMemOperand(dst, i * kPointerSize));
+  int remain = field_count % (DwVfpRegister::kSizeInBytes / kPointerSize);

[ulan, 2013/04/12 14:07:04]

This works when:
STATIC_ASSERT(SwVfpRegister::kSizeInBytes == kPointerSize)
STATIC_ASSERT(2 * SwVfpRegister::kSizeInBytes == DwVfpRegister::kSizeInBytes)

[Rodolph Perfetta, 2013/04/12 14:42:59]

Done.

+  if (remain != 0) {
+    vldr(single_scratch,
+         FieldMemOperand(src, (field_count - 1) * kPointerSize));
+    vstr(single_scratch,
+         FieldMemOperand(dst, (field_count - 1) * kPointerSize));
   }
 }
 
 
 void MacroAssembler::CopyBytes(Register src,
                                Register dst,
                                Register length,
                                Register scratch) {
   Label align_loop, align_loop_1, word_loop, byte_loop, byte_loop_1, done;
 
@@ skipping 668 matching lines @@
 void CodePatcher::EmitCondition(Condition cond) {
   Instr instr = Assembler::instr_at(masm_.pc_);
   instr = (instr & ~kCondMask) | cond;
   masm_.emit(instr);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM