llvm IR常用指令一

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 2024/02/28 

llvm IR常用指令一

终结指令

ret指令

ret < type> < value>;返回特定类型返回值的return指令

ret void;无返回值的return指令

Test:
ret i32 5;返回整数5
ret void;返回无符号
ret { i32 , i8 } { i32 4 , i8 2 };返回结构体

br指令

br i1 < cond>,label < iftrue>,label < iffalse>;有条件跳转

br label < dest>;无条件分支

Test:
%cond = icmp eq i32 %al,%b
br il %cond,label %IfEqual,label %IfUnequal
IfEqual:
ret i32 1
IfUnequal:
ret i32 0

icmp指令

< result> = icmp < cond> < ty> < op1> < op2>;比较两个ty类型的数是否满足条件cond

Test:
<result> = icmp eq i32 4,5      ;false eq=equal
<result> = icmp ne float* %X %X ;false ne=not equal
<result> = icmp ult i16 4, 5    ;true ult=unsigned less than
<result> = icmp sgt i16 4, 5    ;false sgt=signed greater than
<result> = icmp ule i16 -4, 5   ;false ule=unsigned less or equal
<result> = icmp sge i16 4, 5    ;false sge=signed greater or equal

fcmp指令

< result>= fcmp < cond> < ty> < op1> < op2>;比较两个浮点数是否满足条件cond

Test:
<result> = fcmp oeq float 4.0,5.0   ;false oeq=order and equal
<result> = fcmp one float 4.0,5.0   ;true 
<result> = fcmp olt float 4.0,5.0   ;true
<result> = fcmp ueq double 1.0,2.0  ;false

switch指令

switch < intty> < value>, label < defaultdest> [ < intty> < val>,label < dest>…]

Test:
%Val = zext i1 %value to i32
switch i32 %Val,label %truedest[ i32 0,label %falsedest ];与条件跳转等效
switch i32 0,label %dest[ ];与非条件跳转等效
switch i32 %Val,label %otherwise [ i32 0, label %onzero
                                   i32 1, label %onone
                                   i32 2, label %ontwo];三条跳转

二元运算

add指令

< result> = add < ty> < op1>, < op2>

1	<result>=add i32 4,%var;4+%var

sub指令

< result> = sub < ty> < op1>, < op2>

mul指令

< result> = mul < ty> < op1>, < op2>

udiv指令

< result> = udiv < ty> < op1>, < op2>;无符号整除

< result> = udiv exact < ty> < op1>, < op2>;如果结果不是整数会报错

sdiv指令

< result> = sdiv < ty> < op1>, < op2>;有符号整除

< result> = sdiv exact < ty> < op1>, < op2>;如果结果不是整数会报错

urem指令

< result> = urem < ty> < op1>, < op2>；无符号取余

srem指令

< result> = srem < ty> < op1>, < op2>；有符号取余

按位二元运算

shl指令

< result> = shl < ty> < op1>, < op2>；整数左移op1<<op2

lshr指令

< result> = lshr < ty> < op1>, < op2>；整数逻辑右移，会变为无符号类型

ashr指令

< result> = ashr < ty> < op1>, < op2>；整数算数右移

1
2
3

Difference:
<result>=lshr i8 -2,1  ;result=0x7F
<result>=ashr i8 -2,1  ;result=-1

and指令

< result> = and < ty> < op1>, < op2>；整数按位与

or指令

< result> = or < ty> < op1>, < op2>；整数按位或

xor指令

< result> = ashr < ty> < op1>, < op2>；整数按位异或

原文作者：Straw

原文链接：https://straw-233.github.io/2024/02/28/llvm%20IR%E5%B8%B8%E7%94%A8%E6%8C%87%E4%BB%A4%E4%B8%80/

发表日期：February 28th 2024, 9:26:52 pm

更新日期：February 29th 2024, 2:39:56 pm

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