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Quote:

For that specific question, "is the JIT compiler smart enough to resolve those repeated Ldarg_0s into register access?", you'll find the answer with magnitudes less effort (compared to learning the inner workings of a JIT compiler) by compiling and linking the code in a tiny test program, load it into VS and display the disassembly.

Quote:

Another remark: JITting is essentially code generation - including loophole optimization. Code generation is inherently CPU dependent. x86, x64 and ARM require significantly different code generators.

class c {
    char current;
    public void setA(char c) {
      this.current = c;
00EF0DF0  push        ebp  
00EF0DF1  mov         ebp,esp  
00EF0DF3  mov         word ptr [ecx+4],dx  
      if ((this.current >= 'A' && this.current <= 'Z') ||
        (this.current >= 'a' && this.current <= 'z')) {
00EF0DF7  movzx       eax,word ptr [ecx+4]  
00EF0DFB  cmp         eax,41h  
00EF0DFE  jl          Test.c.setA(Char)+015h (0EF0E05h)  
00EF0E00  cmp         eax,5Ah  
00EF0E03  jle         Test.c.setA(Char)+01Fh (0EF0E0Fh)  
00EF0E05  cmp         eax,61h  
00EF0E08  jl          Test.c.setA(Char)+02Ah (0EF0E1Ah)  
00EF0E0A  cmp         eax,7Ah  
00EF0E0D  jg          Test.c.setA(Char)+02Ah (0EF0E1Ah)  
        Console.WriteLine("Argument is an alphabetic character");
00EF0E0F  mov         ecx,dword ptr ds:[3BB24A0h]  
00EF0E15  call        System.Console.WriteLine(System.String) (65A637B8h)  
00EF0E1A  pop         ebp  
00EF0E1B  ret

class c {
    char current;
    public void setA(char c) {
      this.current = c;
00007FFE45A90EE0  sub         rsp,28h  
00007FFE45A90EE4  mov         word ptr [rcx+8],dx  
      if ((this.current >= 'A' && this.current <= 'Z') ||
        (this.current >= 'a' && this.current <= 'z')) {
00007FFE45A90EE8  movzx       ecx,word ptr [rcx+8]  
00007FFE45A90EEC  cmp         ecx,41h  
00007FFE45A90EEF  jl          Test.c.setA(Char)+016h (07FFE45A90EF6h)  
00007FFE45A90EF1  cmp         ecx,5Ah  
00007FFE45A90EF4  jle         Test.c.setA(Char)+020h (07FFE45A90F00h)  
00007FFE45A90EF6  cmp         ecx,61h  
00007FFE45A90EF9  jl          Test.c.setA(Char)+032h (07FFE45A90F12h)  
00007FFE45A90EFB  cmp         ecx,7Ah  
00007FFE45A90EFE  jg          Test.c.setA(Char)+032h (07FFE45A90F12h)  
        Console.WriteLine("Argument is an alphabetic character");
00007FFE45A90F00  mov         rcx,1FE90003938h  
00007FFE45A90F0A  mov         rcx,qword ptr [rcx]  
00007FFE45A90F0D  call        System.Console.WriteLine(System.String) (07FFEA3F80DB0h)  
00007FFE45A90F12  nop  
00007FFE45A90F13  add         rsp,28h  
00007FFE45A90F17  ret

var cur = this.current;
if( cur >= 'A' && cur <= 'Z' || cur >= 'a' && cur <= 'z') {
  // do something
}

int p;
int l;
int c;
ch = -1;
this.capture.Clear();
if ((this.current == -2)) {
    this.Advance();
}
p = this.position;
l = this.line;
c = this.column;
// q0:
// [\t-\n\r ]
if (((((this.current >= 9) 
            && (this.current <= 10)) 
            || (this.current == 13)) 
            || (this.current == 32))) {
    this.Advance();
    goto q1;
}
// [A-Z_hj-kmqxz]
if ((((((((((this.current >= 65) 
            && (this.current <= 90)) 
            || (this.current == 95)) 
            || (this.current == 104)) 
            || ((this.current >= 106) 
            && (this.current <= 107))) 
            || (this.current == 109)) 
            || (this.current == 113)) 
            || (this.current == 120)) 
            || (this.current == 122))) {
    this.Advance();
    goto q2;
}
// [a]
if ((this.current == 97)) {
    this.Advance();
    goto q3;
}
// [b]
if ((this.current == 98)) {
    this.Advance();
    goto q22;
}
// ...snip...
q1:
// [\t-\n\r ]
if (((((this.current >= 9) 
            && (this.current <= 10)) 
            || (this.current == 13)) 
            || (this.current == 32))) {
    this.Advance();
    goto q1;
}
return FAMatch.Create(2, this.capture.ToString(), p, l, c);
q2:
// [0-9A-Z_a-z]
if ((((((this.current >= 48) 
            && (this.current <= 57)) 
            || ((this.current >= 65) 
            && (this.current <= 90))) 
            || (this.current == 95)) 
            || ((this.current >= 97) 
            && (this.current <= 122)))) {
    this.Advance();
    goto q2;
}
return FAMatch.Create(0, this.capture.ToString(), p, l, c);

Quote:

Running the code through a debugger and dropping to assembly. The only way I can do that reliably is with debug info, which may change how the JITter drops native instructions. I can't rely on it.