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Questions and Answers
What does the MIPS instruction 'beq' accomplish?
What does the MIPS instruction 'beq' accomplish?
In the compiled MIPS code for the 'if' statement, what instruction is executed if the condition is false?
In the compiled MIPS code for the 'if' statement, what instruction is executed if the condition is false?
Which of the following correctly describes the unconditional jump instruction in MIPS?
Which of the following correctly describes the unconditional jump instruction in MIPS?
What MIPS instruction would be used to compare if one register is not equal to another in the context of branching?
What MIPS instruction would be used to compare if one register is not equal to another in the context of branching?
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In the provided loop example, which instruction checks if the value of the array element is equal to 'k'?
In the provided loop example, which instruction checks if the value of the array element is equal to 'k'?
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What is the purpose of the 'slt' instruction in MIPS?
What is the purpose of the 'slt' instruction in MIPS?
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In a MIPS loop structure, which instruction is responsible for incrementing the index variable?
In a MIPS loop structure, which instruction is responsible for incrementing the index variable?
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What type of control flow does the instruction 'j L1' implement?
What type of control flow does the instruction 'j L1' implement?
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Study Notes
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/elsestatements, 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 $s4). - Generated MIPS code includes branch instructions to handle conditional logic.
Compiling Loop Statements
- Example C code:
while (save[i] == k) i += 1; -
iin$s3,kin$s5,save's address in$s6. - Data type of
saveis 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 comparersto a constant. -
sltandsltiinstructions can be used in combination withbeqandbneto implement conditional execution.
Signed vs. Unsigned
-
Signed comparison: uses
sltandslti. -
Unsigned comparison: uses
sltuandsltui. - 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. -
beqandbneare common cases for branching. - Simple comparisons
(=, !=)are faster to implement than complex comparisons (<, >).
Example of Pseudo Instructions
- Examples for pseudo instructions like
blt,bge, andble. - Shows how they are implemented using existing MIPS instructions.
Procedure Calling
- Steps for calling a procedure:
- Place parameters in registers.
- Transfer control to procedure
- Acquire storage for procedure.
- Perform procedure's operations.
- Place result in registers for the caller.
- Return control to the caller (using
$raregister).
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
$gpregister 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 $ra -
jalputs the address of the next instruction in register$ra. - Procedure returns by jumping to the address in the register
$ra.
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Description
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.
