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Joe Groff (joe@f.duriansoftware.com)'s status on Thursday, 19-Sep-2024 06:08:16 JST Joe Groff

a while back, someone asked, "why isn't there a way in C to tell if my code is optimized?" thankfully, we can implement this as a library function
In conversation about 5 months ago from f.duriansoftware.com permalink
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1. #include <stdio.h> __attribute__((noinline)) bool is_optimized_impl(int *a, float *b) { *a = 0; *b = 1; return *a == 0; } bool is_optimized() { union { int a; float b; } u; return is_optimized_impl(&u.a, &u.b); } int main() { printf("i am %soptimized\n", is_optimized() ? "" : "not "); }
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  Vegard Nossum 🥑 (vegard@mastodon.social)'s status on Thursday, 19-Sep-2024 19:20:21 JST Vegard Nossum 🥑
  in reply to
  
  @joe This program detects optimization level: https://gcc.godbolt.org/z/G956WzrrE
  In conversation about 5 months ago permalink
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  1. Domain not in remote thumbnail source whitelist: raw.githubusercontent.com
    
    Compiler Explorer - C++
    
    from Matt Godbolt
    
    int x, y; #define def(name, attr) \ __attribute__ ((noinline, noclone, attr)) \ int name() \ { \ a: \ for (int i = 0; i < y; ++i) \ x=&x+!x!=&x==x; \ b: \ return (uintptr_t) &&b - (uintptr_t) &&a; \ } def(fn, ) def(fn0, optimize(0)); def(fn1, optimize(1)); def(fn2, optimize(2)); def(fn3, optimize(3)); int O() { int s = fn(); if (s == fn0()) return 0; if (s == fn1()) return 1; if (s == fn2()) return 2; if (s == fn3()) return 3; return -1; } int main(int argc, char *argv[]) { printf("-O%d\n", O()); return 0; }
  Haelwenn /элвэн/ :triskell: likes this.
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  Haelwenn /элвэн/ :triskell: (lanodan@queer.hacktivis.me)'s status on Thursday, 19-Sep-2024 19:23:08 JST Haelwenn /элвэн/ :triskell:
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  - Vegard Nossum 🥑
  @vegard @joe Well with the optimize attribute it's less tricky to understand.
  
  In conversation about 5 months ago permalink

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