How to dump scheduling graph?

78. How to dump scheduling graph?
/home/jtony/git-llvm/build/team-llvm/bin/llc /home/jtony/scrum/s11/memcpy/jtony/ppc.ll -view-misched-dags 2>&1 | /home/sfertile/bin/capture_dot
test/CodeGen/PowerPC/reduced.ll

79. How to show hidden llc options?
llc -help-hidden
like:
 -view-misched-dags                                       - Pop up a window to show MISched dags after they are processed
 -view-sched-dags                                         - Pop up a window to show sched dags as they are processed
 -view-sunit-dags                                         - Pop up a window to show SUnit dags after they are processed

What is llvm-dis?

The llvm-dis command is the LLVM disassembler. It takes an LLVM bitcode file and converts it into human-readable LLVM assembly language.

If the input is being read from standard input, then llvm-dis will send its output to standard output by default. Otherwise, the output will be written to a file named after the input file, with a .ll suffix added (any existing .bc suffix will first be removed). You can override the choice of output file using the -o option.

迭代文件中的行、单词和字符

1. 迭代文件中的每一行

• while 循环法

while read line;

do

echo $line;

done < file.txt

改成子shell:

cat file.txt | (while read line;do echo $line;done)

• awk法：

cat file.txt| awk '{print}'

2.迭代一行中的每一个单词

for word in $line;

do 

echo $word;

done

3. 迭代每一个字符

${string:start_pos:num_of_chars}：从字符串中提取一个字符；(bash文本切片）

${#word}:返回变量word的长度

for((i=0;i<${#word};i++))

do

echo ${word:i:1);

done

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LDUX/ldux ( Load Doubleword with Update Indexed)

Load Doubleword with Update Indexed
X-form
ldux RT,RA,RB

31 RT RA RB 53 /
0  6  11 16 21 31

EA <= (RA) + (RB)
RT <= MEM(EA, 8)
RA <= EA

Let the effective address (EA) be the sum (RA)+ (RB).
The doubleword in storage addressed by EA is loaded
into RT.
EA is placed into register RA.
If RA=0 or RA=RT, the instruction form is invalid.
Special Registers Altered:
None

D-Form VS X-Form

20. D-Form VS X-Form
D-Form is the immediate/register addressing mode.
X-Form is the register/register addressing mode.
Otherwise known as unindexed and indexed loads respectivelly
So if you have a series consecutive loads, the D-Form loads have a huge advantage.
Because with X-Form loads you have to have the offset in a register so you get consecutive
 offsets by either using multiple registers or having instructions in between to increment the offset.

call back function

C Callbacks

Callbacks have a wide variety of uses, for example in error signaling: a Unix program might not want to terminate immediately when it receives SIGTERM, so to make sure that its termination is handled properly, it would register the cleanup function as a callback. Callbacks may also be used to control whether a function acts or not: Xlib allows custom predicates to be specified to determine whether a program wishes to handle an event.
The following C code demonstrates the use of callbacks to display two numbers.

#include <stdio.h>
#include <stdlib.h>

/* The calling function takes a single callback as a parameter. */
void PrintTwoNumbers(int (*numberSource)(void)) {
    printf("%d and %d\n", numberSource(), numberSource());
}

/* A possible callback */
int overNineThousand(void) {
    return (rand()%1000) + 9001;
}

/* Another possible callback. */
int meaningOfLife(void) {
    return 42;
}

/* Here we call PrintTwoNumbers() with three different callbacks. */
int main(void) {
    PrintTwoNumbers(&rand);
    PrintTwoNumbers(&overNineThousand);
    PrintTwoNumbers(&meaningOfLife);
    return 0;
}

This should provide output similar to:

125185 and 89187225
 9084 and 9441
 42 and 42

From 

知乎

作者：桥头堡
链接：https://www.zhihu.com/question/19801131/answer/27459821
来源：知乎
著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。

什么是回调函数？
我们绕点远路来回答这个问题。
编程分为两类：系统编程（system programming）和应用编程（application programming）。所谓系统编程，简单来说，就是编写库；而应用编程就是利用写好的各种库来编写具某种功用的程序，也就是应用。系统程序员会给自己写的库留下一些接口，即API（application programming interface，应用编程接口），以供应用程序员使用。所以在抽象层的图示里，库位于应用的底下。
当程序跑起来时，一般情况下，应用程序（application program）会时常通过API调用库里所预先备好的函数。但是有些库函数（library function）却要求应用先传给它一个函数，好在合适的时候调用，以完成目标任务。这个被传入的、后又被调用的函数就称为回调函数（callback function）。
打个比方，有一家旅馆提供叫醒服务，但是要求旅客自己决定叫醒的方法。可以是打客房电话，也可以是派服务员去敲门，睡得死怕耽误事的，还可以要求往自己头上浇盆水。这里，“叫醒”这个行为是旅馆提供的，相当于库函数，但是叫醒的方式是由旅客决定并告诉旅馆的，也就是回调函数。而旅客告诉旅馆怎么叫醒自己的动作，也就是把回调函数传入库函数的动作，称为登记回调函数（to register a callback function）。如下图所示（图片来源：维基百科）：


可以看到，回调函数通常和应用处于同一抽象层（因为传入什么样的回调函数是在应用级别决定的）。而回调就成了一个高层调用底层，底层再回过头来调用高层的过程。（我认为）这应该是回调最早的应用之处，也是其得名如此的原因。

LXVD2X/lxvd2x (Load VSX Vector Doubleword*2 Indexed)

Load VSX Vector Doubleword*2 Indexed


X-form
lxvd2x XT,RA,RB

31 T RA RB 844 TX
0 6 11 16 21 31
if MSR.VSX=0 then VSX_Unavailable()
EA <= RA=0 ? GPR[RB] : GPR[RA] + GPR[RB]
VSR[32×TX+T].dword[0] <= MEM(EA, 8)
VSR[32×TX+T].dword[1] <= MEM(EA+8, 8)





Let XT be the value 32×TX + T.
Let EA be the sum of the contents of GPR[RA], or 0 if RA
is equal to 0, and the contents of GPR[RB].
For each integer value i from 0 to 1, do the following.

When Big-Endian byte ordering is employed, the
contents of the doubleword in storage at address
EA+8×i are placed into load_data in such an order
that;
– the contents of the byte in storage at address
EA+8×i are placed into byte element 0 of
load_data,
– the contents of the byte in storage at address
EA+8×i+1 are placed into byte element 1 of
load_data, and so forth until
– the contents of the byte in storage at address
EA+8×i+7 are placed into byte element 7 of
load_data.
When Little-Endian byte ordering is employed, the
contents of the doubleword in storage at address
EA+8×i are placed into load_data in such an order
that;
– the contents of the byte in storage at address
EA+8×i are placed into byte element 7 of
load_data,
– the contents of the byte in storage at address
EA+8×i+1 are placed into byte element 6 of
load_data, and so forth until