Yang_Jialin@xxxxxxx writes: > About the prefetch data of gcc, with optimization option "-O0", some gcc > versions have defined "prefetch" and ''prefetchw" function, whether with > operations or not. > But for other gcc versions , they have not been defined, e.g. 3.4 . I am > now confused about what version defines it and which not. Can you tell > me about this? BUILT_IN_PREFETCH was added here: r47582 | janis | 2001-12-04 00:50:35 +0000 (Tue, 04 Dec 2001) | 6 lines * builtin-types.def (BT_FN_VOID_PTR_INT_INT): New. * builtins.def (BUILT_IN_PREFETCH): New. * builtins.c (expand_builtin_expect): New. (expand_builtin): Call it. * doc/extend.texi: Document __builtin_expect. So every version of gcc that branched since then has it. That would be, I think, 3.1 onwards. Whether __builtin_prefetc does anything or not depends on the particular back end you're using. Andrew.