MIPS Control Flow Instructions Quiz

MIPS Case Study (Control Flow Instructions)

• MIPS architecture is a case study in control flow instructions.
• The lecture material (471029: Introduction to Computer Architecture, 11th Lecture) is primarily based on COD 5th edition textbook.
• Prof. Dohyung Kim, and the computer architecture course from KAIST and SKKU also contributed.

MIPS Control Flow Instructions

• Conditional operations: Instructions branch to a labeled instruction if a condition is true.

• Instructions continue sequentially if the condition is false.

• beq (branch on equal): if (rs == rt) branch to instruction labeled L1;

• bne (branch on not equal): if (rs != rt) branch to instruction labeled L1;

• j (jump): unconditional jump to instruction labeled L1;

• Example C code translates to MIPS code using if/else statements, and registers.

Compiling If Statements

• Example C code: if (i == j) f = g + h; else f = g - h;
• Assumes variables are in specific registers (f, g, h, i, j in $s0, $s1, $s2, $s3, and $s4).
• Generated MIPS code includes branch instructions to handle conditional logic.

Compiling Loop Statements

• Example C code: while (save[i] == k) i += 1;
• i in $s3, k in $s5, save's address in $s6.
• Data type of save is assumed to be word.
• Generated MIPS code includes loop structures and conditional branches.

More Conditional Operations

• Set result to 1 if a condition is true using slt (set less than).
• if (rs < rt) rd = 1, else rd= 0;.
• if (rs < constant) rt = 1, else rt = 0;.
• slti (set less than immediate), can be used to compare rs to a constant.
• slt and slti instructions can be used in combination with beq and bne to implement conditional execution.

Signed vs. Unsigned

• Signed comparison: uses slt and slti.
• Unsigned comparison: uses sltu and sltui.
• Shows examples where comparing signed vs unsigned integers produce different results.

Aside: Basic Blocks

• A basic block is a sequence of instructions.
• There are no embedded branches (branches only at end).
• No branch targets (targets only at start).
• Compilers identify basic blocks to optimize code.
• Advanced processors can accelerate execution of basic blocks.

Branch Instruction Design

• Why blt, bge, etc. are not simpler instructions.
• beq and bne are common cases for branching.
• Simple comparisons (=, !=) are faster to implement than complex comparisons (<, >).

Example of Pseudo Instructions

• Examples for pseudo instructions like blt, bge, and ble.
• Shows how they are implemented using existing MIPS instructions.

Procedure Calling

• Steps for calling a procedure:
  1. Place parameters in registers.
  2. Transfer control to procedure
  3. Acquire storage for procedure.
  4. Perform procedure's operations.
  5. Place result in registers for the caller.
  6. Return control to the caller (using $ra register).

MIPS Register Convention

• Describes the usage of different MIPS registers.
• Includes registers' roles for (constants, arguments, temporaries, saved values).
• Registers for special purposes (global pointer, stack pointer, return address, etc.).
• MIPS software reserves the $gp register for static data.

Six Steps in Execution of a Procedure

• Detailed walkthrough of the procedure call process.
• Includes steps and the registers used.
• Shows which registers are argument registers, which are return value registers and which are return address registers.

MIPS Procedure Calls

• Procedure call: uses jal
• Procedure return: is handled by jr $ra
• jal puts the address of the next instruction in register $ra.
• Procedure returns by jumping to the address in the register $ra.

Test your understanding of control flow instructions in MIPS architecture, focusing on branching and jump operations. This quiz covers specific instructions like beq, bne, and j, as well as their implications in programming with C code. Delve into the nuances of MIPS as presented in the 11th lecture of Introduction to Computer Architecture.