火車頭 (信息學競賽)

火車頭是一種信息學競賽中使用的，用來提升代碼運行速度的預處理優化。一般在正規的比賽中被禁止，在正式的開發中亦無應用。通常火車頭中包含大量的冗餘優化以及玄學成分

示例

這是一個常見的火車頭 <syntaxhighlight lang = "cpp">

1. pragma GCC optimize(3)
2. pragma GCC target("avx")
3. pragma GCC optimize("Ofast")
4. pragma GCC optimize("inline")
5. pragma GCC optimize("-fgcse")
6. pragma GCC optimize("-fgcse-lm")
7. pragma GCC optimize("-fipa-sra")
8. pragma GCC optimize("-ftree-pre")
9. pragma GCC optimize("-ftree-vrp")
10. pragma GCC optimize("-fpeephole2")
11. pragma GCC optimize("-ffast-math")
12. pragma GCC optimize("-fsched-spec")
13. pragma GCC optimize("unroll-loops")
14. pragma GCC optimize("-falign-jumps")
15. pragma GCC optimize("-falign-loops")
16. pragma GCC optimize("-falign-labels")
17. pragma GCC optimize("-fdevirtualize")
18. pragma GCC optimize("-fcaller-saves")
19. pragma GCC optimize("-fcrossjumping")
20. pragma GCC optimize("-fthread-jumps")
21. pragma GCC optimize("-funroll-loops")
22. pragma GCC optimize("-fwhole-program")
23. pragma GCC optimize("-freorder-blocks")
24. pragma GCC optimize("-fschedule-insns")
25. pragma GCC optimize("inline-functions")
26. pragma GCC optimize("-ftree-tail-merge")
27. pragma GCC optimize("-fschedule-insns2")
28. pragma GCC optimize("-fstrict-aliasing")
29. pragma GCC optimize("-fstrict-overflow")
30. pragma GCC optimize("-falign-functions")
31. pragma GCC optimize("-fcse-skip-blocks")
32. pragma GCC optimize("-fcse-follow-jumps")
33. pragma GCC optimize("-fsched-interblock")
34. pragma GCC optimize("-fpartial-inlining")
35. pragma GCC optimize("no-stack-protector")
36. pragma GCC optimize("-freorder-functions")
37. pragma GCC optimize("-findirect-inlining")
38. pragma GCC optimize("-fhoist-adjacent-loads")
39. pragma GCC optimize("-frerun-cse-after-loop")
40. pragma GCC optimize("inline-small-functions")
41. pragma GCC optimize("-finline-small-functions")
42. pragma GCC optimize("-ftree-switch-conversion")
43. pragma GCC optimize("-foptimize-sibling-calls")
44. pragma GCC optimize("-fexpensive-optimizations")
45. pragma GCC optimize("-funsafe-loop-optimizations")
46. pragma GCC optimize("inline-functions-called-once")
47. pragma GCC optimize("-fdelete-null-pointer-checks")
48. pragma GCC optimize(2)

</syntaxhighlight> （事實上對於此份優化，僅保留前四行即可）