.NET乘法优化 [英] .NET multiplication optimization

问题描述

编译器是否优化任何乘法1？也就是说，考虑：

Does the compiler optimize out any multiplications by 1? That is, consider:

int a = 1;
int b = 5 * a;

将表达式5 * a优化到5？如果不是，如果a被定义为：

Will the expression 5 * a be optimized into just 5? If not, will it if a is defined as:

const int a = 1;

推荐答案

它会在编译时预先计算任何常量表达式，包括字符串连接。如果没有 const ，它将被单独使用。

It will pre-calculate any constant expressions when it compiles, including string concatenation. Without the const it will be left alone.

IL：

.maxstack 2
.locals init ([0] int32, [1] int32)

ldc.i4.1   //load 1
stloc.0    //store in 1st local variable
ldc.i4.5   //load 5
ldloc.0    //load 1st variable
mul        // 1 * 5
stloc.1    // store in 2nd local variable 

b $ b

第二个示例编译为：

The second example compiles to this:

.maxstack 1
.locals init ( [0] int32 )

ldc.i4.5 //load 5 
stloc.0  //store in local variable

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