Use const internally in corelib for Environment.NewLine

[stephentoub]

Anywhere Environment.NewLine was being used internal to corelib, instead changes it to use an internal Environment.NewLineConst, which is just a const string. The main benefit of that is places where it's then concatenated with another const allows the C# compiler to do the concat at compile time rather than at run time.

Where I was already touching the code, fixed a few places where additional strings were being created unnecessarily, e.g. s += a; s += b; will do two string.Concat calls each with two arguments, whereas s += a + b; will do just one string.Concat call with three arguments.

[EgorBo]

Shouldn't Environment.NewLine be an intrinsic instead? Like BitConverter.IsLittleEndian or string.Empty?

UPD: ah, I guess JIT is not able to concat const strings yet (but would be nice to be able to fold CNS_STR nodes, I think it's not difficult to implement: #26000 (comment))

[stephentoub]

I guess JIT is not able to concat const strings yet (but would be nice to be able to fold CNS_STR nodes, I think it's not difficult to implement

It of course could be done, but it'd be more than just handling constant strings... the JIT would need to unwind decisions the C# compiler makes about what overloads of string.Concat to use.

[EgorBo]

I guess JIT is not able to concat const strings yet (but would be nice to be able to fold CNS_STR nodes, I think it's not difficult to implement

It of course could be done, but it'd be more than just handling constant strings... the JIT would need to unwind decisions the C# compiler makes about what overloads of string.Concat to use.

I mean at least simple cases, e.g. (from your changes):

text.Append(Environment.NewLine + InnerExceptionPrefix);

So JIT in runtime should replace Environment.NewLine with CNS_STR (const string) because its value never changes. Environment.NewLine + InnerExceptionPrefix is:

\--*  CALL      ref    String.Concat
   +--*  CALL      ref    Environment.get_NewLine
   \--*  CNS_STR   ref   <string constant>

then is converted into:

\--*  CALL      ref    String.Concat
   +--*  CNS_STR   ref   <string constant>   ;; it's now a const
   \--*  CNS_STR   ref   <string constant>

then JIT should fold it into just

\--*  CNS_STR   ref   <string constant>