○ This changes the format and structure of the code but preserves the semantics (what it does)○ Can change lots of details for optimization, as long as the overall effect is the same

The most general form is shown at the bottomof the table with syntax Imm(rb,ri,s). Such a reference has four components: animmediate offset Imm, a base register rb, an index register ri, and a scale factors, where s must be 1, 2, 4, or 8. Both the base and index must be 64-bit registers.The effective address is computed as Imm + R[rb] + R[ri] . s.

C declaration Intel data type Assembly-code suffix Size (bytes)

A final difference is that we see two additional lines of code (lines8–9). These instructions will have no effect on the program, since they occur afterthe return instruction (line 7). They have been inserted to grow the code for thefunction to 16 bytes, enabling a better placement of the next block of code in termsof memory system performance.

Its main feature isthat it is in a more readable textual format, as compared to the binary format ofmachine code.