877-CS4100： 计算机结构Instruction Set Architecture.ppt

(Make noise) Back row! You in the (describe clothing)! I do a load byte from t0 to t1. What do I get in t1? F7? Is there anything you would like to add to your statement? So your final answer is F7? (Alarm.wav) Instruction Set-* Example: Clearing an Array clear1(int array[], int size) { int i; for (i = 0; i size; i += 1) array[i] = 0; } clear2(int *array, int size) { int *p; for (p = array[0]; p array[size]; p = p + 1) *p = 0; } move $t0,$zero # i = 0 loop1: sll $t1,$t0,2 # $t1 = i * 4 add $t2,$a0,$t1 # $t2 = # array[i] sw $zero, 0($t2) # array[i] = 0 addi $t0,$t0,1 # i = i + 1 slt $t3,$t0,$a1 # $t3 = # (i size) bne $t3,$zero,loop1 # if (…) # goto loop1 move $t0, $a0 # p = array[0] sll $t1, $a1, 2 # $t1 = size * 4 add $t2,$a0,$t1 # $t2 = # array[size] loop2: sw $zero,0($t0) # Memory[p] = 0 addi $t0,$t0,4 # p = p + 4 slt $t3,$t0,$t2 # $t3 = #(parray[size]) bne $t3,$zero,loop2 # if (…) # goto loop2 Instruction Set-* Comparison of Array vs. Ptr Multiply “strength reduced” to shift (strength reduction) Array version requires shift to be inside loop Part of index calculation for incremented i c.f. incrementing pointer Compiler can achieve same effect as manual use of pointers Eliminating array address calculations within loop (induction variable elimination): 6 instructions reduced to 4 in loop Better to make program clearer and safer Instruction Set-* Outline Instruction set architecture (using MIPS ISA as an example) Operands Register operands and their organization Memory operands, data transfer Immediate operands Signed and unsigned numbers Representing instructions Operations Logical Decision making and branches Supporting procedures in hardware Communicating with people Addressing for 32