ARM: Improve register allocation and constraints....

src/arm/assembler-arm.h

Index: src/arm/assembler-arm.h
===================================================================
--- src/arm/assembler-arm.h	(revision 8362)
+++ src/arm/assembler-arm.h	(working copy)
@@ -167,13 +167,14 @@
 
 // Double word VFP register.
 struct DwVfpRegister {
-  // d0 has been excluded from allocation. This is following ia32
-  // where xmm0 is excluded. This should be revisited.
-  // Currently d0 is used as a scratch register.
-  // d1 has also been excluded from allocation to be used as a scratch
-  // register as well.
   static const int kNumRegisters = 16;
-  static const int kNumAllocatableRegisters = 15;
+  // A few double registers are reserved: one as a scratch register and one to
+  // hold 0.0, that does not fit in the immediate field of vmov instructions.
+  //  d14: 0.0
+  //  d15: scratch register.
+  static const int kNumReservedRegisters = 2;
+  static const int kNumAllocatableRegisters = kNumRegisters -
+      kNumReservedRegisters;
 
   static int ToAllocationIndex(DwVfpRegister reg) {
     ASSERT(reg.code() != 0);
@@ -188,6 +189,7 @@
   static const char* AllocationIndexToString(int index) {
     ASSERT(index >= 0 && index < kNumAllocatableRegisters);
     const char* const names[] = {
+      "d0",
       "d1",
       "d2",
       "d3",
@@ -200,9 +202,7 @@
       "d10",
       "d11",
       "d12",
-      "d13",
-      "d14",
-      "d15"
+      "d13"
     };
     return names[index];
   }
@@ -306,6 +306,7 @@
 // Aliases for double registers.
 const DwVfpRegister kFirstCalleeSavedDoubleReg = d8;
 const DwVfpRegister kLastCalleeSavedDoubleReg = d15;
+const DwVfpRegister kDoubleRegZero = d14;
 
 
 // Coprocessor register