Avoid memmove when emitting operands in the assembler

and get rid of the mutability of the Operand byte buffer.
Review URL: http://codereview.chromium.org/18656

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1123 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/assembler-ia32-inl.h

@@ -270,8 +270,7 @@ void Assembler::emit_disp(Label* L, Displacement::Type type) {
 }
 
 
-void Operand::set_modrm(int mod,  // reg == 0
-                        Register rm) {
+void Operand::set_modrm(int mod, Register rm) {
   ASSERT((mod & -4) == 0);
   buf_[0] = mod << 6 | rm.code();
   len_ = 1;

src/assembler-ia32.cc

@@ -255,12 +255,6 @@ void Operand::set_disp8(int8_t disp) {
 }
 
 
-void Operand::set_reg(Register reg) const {
-  ASSERT(len_ > 0);
-  buf_[0] = (buf_[0] & ~0x38) | static_cast<byte>(reg.code() << 3);
-}
-
-
 bool Operand::is_reg(Register reg) const {
   return ((buf_[0] & 0xF8) == 0xC0)  // addressing mode is register only.
       && ((buf_[0] & 0x07) == reg.code());  // register codes match.
@@ -2098,10 +2092,18 @@ void Assembler::emit_arith(int sel, Operand dst, const Immediate& x) {
 
 
 void Assembler::emit_operand(Register reg, const Operand& adr) {
-  adr.set_reg(reg);
-  memmove(pc_, adr.buf_, adr.len_);
-  pc_ += adr.len_;
-  if (adr.len_ >= sizeof(int32_t) && adr.rmode_ != RelocInfo::NONE) {
+  const unsigned length = adr.len_;
+  ASSERT(length > 0);
+
+  // Emit updated ModRM byte containing the given register.
+  pc_[0] = (adr.buf_[0] & ~0x38) | (reg.code() << 3);
+
+  // Emit the rest of the encoded operand.
+  for (unsigned i = 1; i < length; i++) pc_[i] = adr.buf_[i];
+  pc_ += length;
+
+  // Emit relocation information if necessary.
+  if (length >= sizeof(int32_t) && adr.rmode_ != RelocInfo::NONE) {
     pc_ -= sizeof(int32_t);  // pc_ must be *at* disp32
     RecordRelocInfo(adr.rmode_);
     pc_ += sizeof(int32_t);

src/assembler-ia32.h

@@ -260,19 +260,19 @@ class Operand BASE_EMBEDDED {
   bool is_reg(Register reg) const;
 
  private:
-  // Mutable because reg in ModR/M byte is set by Assembler via set_reg().
-  mutable byte buf_[6];
+  byte buf_[6];
   // The number of bytes in buf_.
   unsigned int len_;
   // Only valid if len_ > 4.
   RelocInfo::Mode rmode_;
 
-  inline void set_modrm(int mod,  // reg == 0
-                        Register rm);
+  // Set the ModRM byte without an encoded 'reg' register. The
+  // register is encoded later as part of the emit_operand operation.
+  inline void set_modrm(int mod, Register rm);
+
   inline void set_sib(ScaleFactor scale, Register index, Register base);
   inline void set_disp8(int8_t disp);
   inline void set_dispr(int32_t disp, RelocInfo::Mode rmode);
-  inline void set_reg(Register reg) const;
 
   friend class Assembler;
 };