神威芯片汇编指令运行情况

1. 概述

本文分析了神威芯片的指令运行情况，会通过几个例子中来查看。

2. 详述

2.1. 示例一

首先看一个简单的加法例子，代码如下：

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// test.c

int test()
{
    int a = 1;
    int b = 2;
    int c = a + b;
    return c;
}

使用如下命令编译出.o并进行反汇编：

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tecocc -c -device-only -ffp-contract=fast test.c -O0
tecoobjdump -Dr test.o

注意使用了O0优化度，可以查看最原始的汇编，代码如下：

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0000000000000000 <slave_test>:
       0: e0 ff 9e e7   ldi     $30, -32($30)
       4: 1d 00 de c3   stl     $15, 24($30)
       8: 20 00 de e3   ldi     $15, 32($30)
       c: f7 ff 0f b4   stw     $16, -12($15)
      10: f3 ff 4f b4   stw     $17, -16($15)
      14: f6 ff 4f b0   ldw     $1, -12($15)
      18: f2 ff 8f b0   ldw     $2, -16($15)
      1c: 01 00 42 40   addw    $1, $2, $1
      20: ef ff 4f b0   stw     $1, -20($15)
      24: ee ff 0f b0   ldw     $0, -20($15)
      28: e0 ff 8f e7   ldi     $30, -32($15)
      2c: 1c 00 de c3   ldl     $15, 24($30)
      30: 20 00 9e e7   ldi     $30, 32($30)
      34: 01 60 da 07   call    $31, ($26), 1

其中，$30为栈指针，$15为帧指针，$31为默认0，$26为返回地址，$0为整数类型返回值。栈变化如下图所示：

这个例子还是比较简单的，看一个调用的例子。

2.2. 示例二

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int add(int a, int b)
{
    int c = a + b;
    return c;
}

int test()
{
    int a = 1;
    int b = 2;
    int c = add(a, b);
    return c;
}

汇编代码如下：

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0000000000000000 <slave_add>:
       0: e0 ff 9e e7  	ldi	$30, -32($30)
       4: 1d 00 de c3  	stl	$15, 24($30)
       8: 20 00 de e3  	ldi	$15, 32($30)
       c: f7 ff 0f b4  	stw	$16, -12($15)
      10: f3 ff 4f b4  	stw	$17, -16($15)
      14: f6 ff 4f b0  	ldw	$1, -12($15)
      18: f2 ff 8f b0  	ldw	$2, -16($15)
      1c: 01 00 42 40  	addw	$1, $2, $1
      20: ef ff 4f b0  	stw	$1, -20($15)
      24: ee ff 0f b0  	ldw	$0, -20($15)
      28: e0 ff 8f e7  	ldi	$30, -32($15)
      2c: 1c 00 de c3  	ldl	$15, 24($30)
      30: 20 00 9e e7  	ldi	$30, 32($30)
      34: 01 60 da 07  	call	$31, ($26), 1

0000000000000000 <slave_test>:
       0: 00 00 5b f7  	ldih	$29, 0($27)
		0000000000000000:  R_SWAI_GPDISP	.text1.slave_test+0x4
       4: 00 00 5d e7  	ldi	$29, 0($29)
       8: e0 ff 9e e7  	ldi	$30, -32($30)
       c: 1d 00 9e c6  	stl	$26, 24($30)
      10: 15 00 de c3  	stl	$15, 16($30)
      14: 20 00 de e3  	ldi	$15, 32($30)
      18: 01 00 5f e0  	ldi	$1, 1($31)
      1c: ef ff 4f b0  	stw	$1, -20($15)
      20: 02 00 5f e0  	ldi	$1, 2($31)
      24: eb ff 4f b0  	stw	$1, -24($15)
      28: ee ff 0f b4  	ldw	$16, -20($15)
      2c: ea ff 4f b4  	ldw	$17, -24($15)
      30: 04 00 5d c0  	ldl	$1, 0($29)
		0000000000000030:  R_SWAI_LITERAL	slave_add
      34: 1b 4e 5f 40  	or	$1, $31, $27
      38: 00 60 9b 06  	call	$26, ($27), 0
		0000000000000038:  R_SWAI_LITUSE	slave_add+0x3
      3c: 00 00 5a f7  	ldih	$29, 0($26)
		000000000000003c:  R_SWAI_GPDISP	.text1.slave_test+0x4
      40: 00 00 5d e7  	ldi	$29, 0($29)
      44: e7 ff 0f b0  	stw	$0, -28($15)
      48: e6 ff 0f b0  	ldw	$0, -28($15)
      4c: e0 ff 8f e7  	ldi	$30, -32($15)
      50: 14 00 de c3  	ldl	$15, 16($30)
      54: 1c 00 9e c6  	ldl	$26, 24($30)
      58: 20 00 9e e7  	ldi	$30, 32($30)
      5c: 01 60 da 07  	call	$31, ($26), 1

可以看到slave_add跟刚刚示例一中的汇编代码完全一致，就不多看了，主要关注slave_test。其中，$16和$17为参数寄存器。栈变化图如下所示：