[mono] Optimize "constant_string".Length

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Stale
Tech stack
csharp
Domain
compilers, performance

Research direction

No source file, test, or entry point is named. Start by reading the related mono#5310 discussion and tracing the runtime's constant_string.Length optimization path; done means the example folds to 5 and the generated assembly no longer loads the string length from memory.

Written by the indexing model from the issue text.

Description

area-Codegen-JIT-mono 
static int Test() => "Hello".Length; // replace with just `5`

Before:

movabs rax,0x7fd6c1758160
mov    eax,DWORD PTR [rax]
ret

Now:

mov    eax,0x5
ret

Originally posted by @EgorBo in mono#5310

Related:

Dominant language
C#
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