/*---------------------------------------------------------------*/
/*--- High-level IR description ---*/
/*---------------------------------------------------------------*/

/* Vex IR is an architecture-neutral intermediate representation.
Unlike some IRs in systems similar to Vex, it is not like assembly
language (ie. a list of instructions). Rather, it is more like the
IR that might be used in a compiler.

相对汇编语言，VEX IR更像是Compiler的中间语言

Code blocks
~~~~~~~~~~~
The code is broken into small code blocks ("superblocks", type:
'IRSB'). Each code block typically represents from 1 to perhaps 50
instructions. IRSBs are single-entry, multiple-exit code blocks.
Each IRSB contains three things:

单入口，多出口的代码块，与Intel Pin中的Trace级别相仿

- a type environment, which indicates the type of each temporary
value present in the IRSB

【实例：】

types_used提示有多少个Temp变量被使用，types数组里面分别保存着每个Temp变量的类型

- a list of statements, which represent code
【实例：】

stmts_size    0x00000003    int
stmts_used    0x00000003    int
-     (*ir_block).stmts[0]  
　　　　tag    Ist_IMark
-     (*ir_block).stmts[1]    
　　　　tag    Ist_WrTmp
-     (*ir_block).stmts[2]
　　　　tag    Ist_Put

Statements也是保存在stmts数组中，stmts_used代表实际上使用的Statements的数目

- a jump that exits from the end the IRSB
【实例：】　　

jumpkind    Ijk_Boring

最后打印出来的结果如下

0x77D699A0: movl %esi,%esp

IRSB {
　　t0:I32 　　t1:I32 　　　　　　　　　　【2个Temp变量】

------ IMark(0x77D699A0, 2, 0) ------ 【3个Statements，包含IMark，但是没有包含最后一条，因为它是对于IP寄存器操作的，是自动的】
　　t0 = GET:I32(32)　　　　　　　　　　 【整条是一个Statements，而GET:I32(32)是Expression】
　　PUT(24) = t0
　　PUT(68) = 0x77D699A2:I32; exit-Boring

其中， 第二条Statements可以继续分解

-     (*ir_block).stmts[1]
　　　　tag    Ist_WrTmp
　　　　　　　　.tmp    0　　
　　　　　　　　　　　　.tag    Iex_Get
　　　　　　　　　　　　　　　　.offset    32
　　　　　　　　　　　　　　　　.ty    Ity_I32

Because the blocks are multiple-exit, there can be additional
conditional exit statements that cause control to leave the IRSB
before the final exit. Also because of this, IRSBs can cover
multiple non-consecutive sequences of code (up to 3). These are
recorded in the type VexGuestExtents (see libvex.h).

Statements and expressions
~~~~~~~~~~~~~~~~~~~~~~~~~~
Statements (type 'IRStmt') represent operations with side-effects,
eg. guest register writes, stores, and assignments to temporaries.
Expressions (type 'IRExpr') represent operations without
side-effects, eg. arithmetic operations, loads, constants.
Expressions can contain sub-expressions, forming expression trees,
eg. (3 + (4 * load(addr1)).

Statements可以有Side-Effects，但是Expressions是Pure的，没有副作用的。

ST代表从寄存器到内存的数据转移， LD代表从内存到寄存器转移数据

Expression的类型

typedef
   enum { 
      Iex_Binder=0x15000,
      Iex_Get,
      Iex_GetI,
      Iex_RdTmp,
      Iex_Qop,
      Iex_Triop,
      Iex_Binop,
      Iex_Unop,
      Iex_Load,
      Iex_Const,
      Iex_Mux0X,
      Iex_CCall
   }
   IRExprTag;

 Statements的类型

typedef 
   enum {
      Ist_NoOp=0x19000,
      Ist_IMark,     /* META */
      Ist_AbiHint,   /* META */
      Ist_Put,
      Ist_PutI,
      Ist_WrTmp,
      Ist_Store,
      Ist_CAS,
      Ist_LLSC,
      Ist_Dirty,
      Ist_MBE,       /* META (maybe) */
      Ist_Exit
   } 
   IRStmtTag;