崔添翼 § 翼若垂天之云

（本文是 http://llvm.org/releases/2.9/docs/LangRef.html 的阅读笔记，前作为《LLVM笔记(1)：LLVM的语言（上）》。）

• Type System
• Type Classifications
• integer: i1, i2, i3, … i8, … i16, … i32, … i64
• floating point: float, double, x86_fp80, fp128, ppc_fp128
• first class: integer, floating point, pointer, vector, structure, array, label, metadata.
• primitive: label, void, integer, floating point, x86mmx, metadata.
• derived: array, function, pointer, structure, packed structure, vector, opaque.
• Array type

• [<# elements> x <elementtype>]

• Function Type

• <returntype> (<parameter list>)

• Structure Type

• { <type list> }

• Packed Structure Type

• < { <type list> } >

• Pointer Type

• <type> *

• Vector Type

• < <# elements> x <elementtype> >

• Opaque Type: represents unknown type
• Type Up-references
• needed by the asmprinter for printing out cyclic types
• Constants
• Simple Constants
• Boolean(true, false)
• Integer(e.g. 42)
• Floating point(3.14 or 6.02E+23 or double 0x432ff973cafa8000 (IEEE))
• Null pointer (null)
• Complex Constants
• Structure constants
• { i32 4, float 17.0, i32* @G }
• @G = external global i32
• Array constants
• [ i32 42, i32 11, i32 74 ]
• Vector constants
• [ i32 42, i32 11, i32 74 ]
• Zero initialization
• zeroinitializer
• Metadata node
• metadata !{ i32 0, metadata !”test” }
• Global Variable and Function Addresses
• Undefined Values
• The string ‘undef’ can be used anywhere a constant is expected, and indicates that the user of the value may receive an unspecified bit-pattern.
• Trap Values
• Addresses of Basic Blocks
• blockaddress(@function, %block)
• Constant Expressions
• trunc, zext, sext, fptrunc, fpext, fptoui, fptosi, uitofp, sitofp, ptrtoint, inttoptr, bitcast
• getelementptr, select, icmp, fcmp, extractelement, insertelement, shufflevector, extractvalue, insertvalue
• OPCODE
• Other Values
• Inline Assembler Expressions
• Inline Asm Metadata
• Metadata Nodes and Metadata Strings
• Intrinsic Global Variables
• The ‘llvm.used’ Global Variable
• The @llvm.used global is an array with i8* element type which has appending linkage.
• The ‘llvm.compiler.used’ Global Variable
• The ‘llvm.global_ctors’ Global Variable
• The ‘llvm.global_dtors’ Global Variable

（本文是 http://llvm.org/releases/2.9/docs/LangRef.html 的阅读笔记，前作为《LLVM笔记(0)：在一切开始之前》。）

• 一句话总结： LLVM is a Static Single Assignment (SSA) based representation that provides type safety, low-level operations, flexibility, and the capability of representing ‘all’ high-level languages cleanly. It is the common code representation used throughout all phases of the LLVM compilation strategy.
• LLVM语言有三种形式：in-memory compiler IR, on-disk bitcode representation, human readable assembly language representation。三种表现形式是等价的。
• LLVM语言的目标是：一方面 light-weight and low-level，另一方面expressive, typed, and extensible。
• “universal IR”
• Identifiers
• global: @开头
• local: %开头
• ‘;’开始注释
• High Level Structure
• Module
• llvm linker to combine
• global values: functions and global variables
• linkage types
• private, linker_private, linker_private_weak, linker_private_weak_def_auto
• internal, available_externally, linkonce, weak, common, appending, extern_weak
• linkonce_odr, weak_odr
• externally visible (default)
• Calling Conventions
• ccc: the C calling convention
• fastcc: the fast calling convention
• coldcc: the cold calling convention
• Visibility styles (for global variables and functions):
• default, hidden, protected
• Named types
• e.g. %mytype = type { %mytype*, i32 }
• Global variables
• many aspects can be controlled
• Functions
• definition and declaration
• definition contains a list of basic blocks, Control Flow Graph for the function
• each basic block optionally starts with a label, contains a list of instructions, and ends with a terminator instruction
• first basic block is special: 1. immediately executed on entrance; 2. not allowed to have predecessors
• Aliases
• Named Metadata: a collection of metadata
• Parameter Attributes
• zeroext, signext, inreg, byval, sret, noalias, nocapture, nest
• Garbage Collector Names
• Function Attributes
• …
• Module-Level Inline Assembly
• Data Layout
• target datalayout = “layout specification”
• Pointer Aliasing Rules
• memory access must be through pointers
• a pointer value is based on another pointer value according to the rules
• Volatile Memory Accesses