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Comment by glandium | Hacker News Reader

So, running under perf stat tells me the luajit version runs very much more instructions (5M vs. 3M with my patched C version), but they run in the same number of cycles (2.5M), with the luajit version using more instructions per cycle. The unpatched C version uses 3.5M instructions, and 3.5M cycles, which is half the number of instructions per cycle compared to the luajit version.

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How did you patch it? Just compile with "-fno-plt" or something more?

  diff --git a/hello.c b/hello.c
  index 725d5ec..b7b1745 100644
  --- a/hello.c
  +++ b/hello.c
  @@ -1,3 +1,5 @@
  +#define _GNU_SOURCE
  +#include <dlfcn.h>
   #include <stdio.h>
   #include "newplus/plus.h"

  @@ -7,8 +9,9 @@ void run(int count)
       long long end;
       
       int x = 0;
  +    int (*_plusone)(int) = dlsym(RTLD_DEFAULT, "plusone");
       while (x < count)
  -        x = plusone(x);
  +        x = _plusone(x);
       
       printf("%lld\n", current_timestamp() - start);
   }

And you need to add -ldl to the link flags.

Edit: but yeah, -fno-plt works too.

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