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c#.netoptimizationmultiplication

.NET multiplication optimization

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

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

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

const int a = 1;
Solution

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

    Your first example compiles to this 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

    The second example compiles to this:

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

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