[optimizing] Tune some x86_64 moves

Generate Moves of constant FP values by loading from the constant table.

Use 'movl' to load a 64 bit register for positive 32-bit values, saving
a byte in the generated code by taking advantage of the implicit
zero extension.

Change a couple of xorq(reg, reg) to xorl to (potentially) save a byte
of code per xor.

Change-Id: I5b2a807f0d3b29294fd4e7b8ef6d654491fa0b01
Signed-off-by: Mark Mendell <mark.p.mendell@intel.com>
diff --git a/compiler/optimizing/code_generator_x86_64.h b/compiler/optimizing/code_generator_x86_64.h
index 13f9c46..480ea6b 100644
--- a/compiler/optimizing/code_generator_x86_64.h
+++ b/compiler/optimizing/code_generator_x86_64.h
@@ -282,6 +282,9 @@
   Address LiteralInt32Address(int32_t v);
   Address LiteralInt64Address(int64_t v);
 
+  // Load a 64 bit value into a register in the most efficient manner.
+  void Load64BitValue(CpuRegister dest, int64_t value);
+
  private:
   // Labels for each block that will be compiled.
   GrowableArray<Label> block_labels_;