[Interpreter] Bytecodes for exchanging registers.

src/interpreter/bytecodes.h

Index: src/interpreter/bytecodes.h
diff --git a/src/interpreter/bytecodes.h b/src/interpreter/bytecodes.h
index 5af551376893d3c1bf3c1f1df87e475343eb530f..9bea3913d37577c9b40d11f184e0e05049b011f5 100644
--- a/src/interpreter/bytecodes.h
+++ b/src/interpreter/bytecodes.h
@@ -29,8 +29,9 @@ namespace interpreter {
   V(MaybeReg8, OperandSize::kByte) \
                                    \
   /* Short operands. */            \
+  V(Idx16, OperandSize::kShort)    \

[rmcilroy, 2016/01/04 11:54:54]

nit - alphabetical ordering?

[oth, 2016/01/04 14:01:42]

Done.

   V(Count16, OperandSize::kShort)  \
-  V(Idx16, OperandSize::kShort)
+  V(Reg16, OperandSize::kShort)
 
 // The list of bytecodes which are interpreted by the interpreter.
 #define BYTECODE_LIST(V)                                                       \
@@ -78,6 +79,8 @@ namespace interpreter {
                                                                                \
   /* Register-register transfers */                                            \
   V(Mov, OperandType::kReg8, OperandType::kReg8)                               \
+  V(Exchange, OperandType::kReg8, OperandType::kReg16)                         \

[rmcilroy, 2016/01/04 11:54:54]

Is it worth having the non-wide version? It only saves a byte, and we should
only hopefully not hit the exchange path too often (otherwise we have more to
worry about, with the extra exchange bytecodes and the extra byte here wouldn't
have much impact). WDYT?

[oth, 2016/01/04 14:01:42]

I've not found a case that would need it in the next stage of this change. Also
have not found any cases that'd benefit from ExchangeWide either and will pull
it if this continues to be the case.

+  V(ExchangeWide, OperandType::kReg16, OperandType::kReg16)                    \
                                                                                \
   /* LoadIC operations */                                                      \
   V(LoadICSloppy, OperandType::kReg8, OperandType::kIdx8, OperandType::kIdx8)  \
@@ -254,10 +257,7 @@ class Register {
 
   Register() : index_(kIllegalIndex) {}
 
-  explicit Register(int index) : index_(index) {
-    DCHECK_LE(index_, kMaxRegisterIndex);
-    DCHECK_GE(index_, kMinRegisterIndex);
-  }
+  explicit Register(int index) : index_(index) {}
 
   int index() const {
     DCHECK(index_ != kIllegalIndex);
@@ -285,6 +285,9 @@ class Register {
   static Register FromOperand(uint8_t operand);
   uint8_t ToOperand() const;
 
+  static Register FromWideOperand(uint16_t operand);
+  uint16_t ToWideOperand() const;
+
   static bool AreContiguous(Register reg1, Register reg2,
                             Register reg3 = Register(),
                             Register reg4 = Register(),