[BoppreH]

What version of GCC are you using? For me both versions perform the same, both on Ubuntu and Windows:

    $ time ./lone 1000 1
        851000

        real    0m3.578s
        user    0m3.574s
        sys     0m0.004s
        
    $ time ./ltwo 1000 1
        851000

        real    0m3.583s
        user    0m3.583s
        sys     0m0.000s

    $ gcc --version
        gcc (Ubuntu 9.4.0-1ubuntu1~20.04.1) 9.4.0
        Copyright (C) 2019 Free Software Foundation, Inc.
        This is free software; see the source for copying conditions.  There is NO
        warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[torstenvl]

Sorry, I write 'gcc' purely out of force of habit. I'm using Clang/LLVM.

    [17:23:00 user@boxer ~/looptest] $ uname -a
    Darwin boxer.local 21.6.0 Darwin Kernel Version 21.6.0: Thu Jun  8 23:57:12 PDT 2023; root:xnu-8020.240.18.701.6~1/RELEASE_X86_64 x86_64
    [17:23:47 user@boxer ~/looptest] $ cc -v
    Apple clang version 14.0.0 (clang-1400.0.29.202)
    Target: x86_64-apple-darwin21.6.0
    Thread model: posix
    InstalledDir: /Library/Developer/CommandLineTools/usr/bin

Clang generates the sete instruction for me with the above code:

    [17:23:49 user@boxer ~/looptest] $ gcc -c -O3 loop2.c   
    [17:25:00 user@boxer ~/looptest] $ objdump -d --symbolize-operands --x86-asm-syntax=intel --no-show-raw-insn loop2.o
    
    loop2.o: file format mach-o 64-bit x86-64
    
    Disassembly of section __TEXT,__text:
    
    0000000000000000 <_run_switches>:
           0:       push rbp
           1:       mov rbp, rsp
           4:       xor eax, eax
           6:       nop word ptr cs:[rax + rax]
    <L0>:
          10:       movzx ecx, byte ptr [rdi]
          13:       add rdi, 1
          17:       xor edx, edx
          19:       cmp cl, 115
          1c:       sete dl
          1f:       add eax, edx
          21:       xor edx, edx
          23:       cmp cl, 112
          26:       sete dl
          29:       sub eax, edx
          2b:       test cl, cl
          2d:       jne  <L0>
          2f:       pop rbp
          30:       ret