ARM: Make use of d16-d31 when available.

src/arm/code-stubs-arm.h

Index: src/arm/code-stubs-arm.h
diff --git a/src/arm/code-stubs-arm.h b/src/arm/code-stubs-arm.h
index 0443cf799cc08e5d83e8ebe88f6de929dc8b5d12..ed6561cb5583aba558887887e6719529aaa35439 100644
--- a/src/arm/code-stubs-arm.h
+++ b/src/arm/code-stubs-arm.h
@@ -472,9 +472,10 @@ class RecordWriteStub: public CodeStub {
         CpuFeatures::Scope scope(VFP2);
         masm->sub(sp,
                   sp,
-                  Operand(kDoubleSize * (DwVfpRegister::kNumRegisters - 1)));
+                  Operand(kDoubleSize * (DwVfpRegister::NumAvailableRegisters() - 1)));
         // Save all VFP registers except d0.
-        for (int i = DwVfpRegister::kNumRegisters - 1; i > 0; i--) {
+        // XXX: Why is d0 special? It's not the scratch register..

[Rodolph Perfetta, 2012/12/05 00:42:10]

A long time ago, d0 was the scratch register, so this may be a remain from this
time. This method is currently saving callee saved register too.

[hans, 2012/12/05 14:12:58]

So I guess what we want here is to save d0--d7, and d16--d31 when available?
(Same below)

+        for (int i = DwVfpRegister::NumAvailableRegisters() - 1; i > 0; i--) {
           DwVfpRegister reg = DwVfpRegister::from_code(i);
           masm->vstr(reg, MemOperand(sp, (i - 1) * kDoubleSize));
         }
@@ -486,13 +487,14 @@ class RecordWriteStub: public CodeStub {
       if (mode == kSaveFPRegs) {
         CpuFeatures::Scope scope(VFP2);
         // Restore all VFP registers except d0.
-        for (int i = DwVfpRegister::kNumRegisters - 1; i > 0; i--) {
+        // XXX: Why is d0 special? It's not the scratch register..

[Rodolph Perfetta, 2012/12/05 00:42:10]

Ditto.

+        for (int i = DwVfpRegister::NumAvailableRegisters() - 1; i > 0; i--) {
           DwVfpRegister reg = DwVfpRegister::from_code(i);
           masm->vldr(reg, MemOperand(sp, (i - 1) * kDoubleSize));
         }
         masm->add(sp,
                   sp,
-                  Operand(kDoubleSize * (DwVfpRegister::kNumRegisters - 1)));
+                  Operand(kDoubleSize * (DwVfpRegister::NumAvailableRegisters() - 1)));
       }
       masm->ldm(ia_w, sp, (kCallerSaved | lr.bit()) & ~scratch1_.bit());
     }