more rex stuff

src/arch/x86_64/encode.rs

@@ -100,7 +100,7 @@ impl Code {
                     }
                     self.prefix32(&dst)?;
                     self.prefix16(encode_width);
-                    if dst.reg.requires_mem_rex() || dst.width == Width::B64 {
+                    if dst.reg.gt8() || dst.width == Width::B64 {
                         self.bytes.push(rex(dst, 0, 0, dst));
                     }
                     self.bytes.push(0xc6 | encode_width.not8());

src/arch/x86_64/reg.rs

@@ -72,10 +72,6 @@ impl Reg {
             || (self.gt4() && self.width == Width::B8 && !self.high)
     }
 
-    pub fn requires_mem_rex(&self) -> bool {
-        self.gt8() || (self.gt4() && self.width == Width::B8 && !self.high)
-    }
-
     pub fn incompatible(&self, other: &Reg) -> bool {
         (self.requires_rex() && other.high) || (self.high && other.requires_rex())
     }