Gdb, why "next" show each line of the source twice?

Question

each, when the “next” command in gdb is used, I found every line of source code twice ----- I am pretty sure that this code is not in any loop. This phenomenon:

(gdb) frame #0 ap_get_client_block (r=0x8560d48, buffer=0xb68501b7 "<?xml version=\"1.0\" encoding=\"utf-8\"?><Root><OperCode>SMS101</OperCode><AppId>SMSMsgFilterReq</AppId><Req><UserMobile>13925237429</UserMobile><SendMsg>abc圲34¨圲23a露07\214圲21￠＜237朲11?东215圲10°＜214朲27￥応227露07\214正常,hao"..., bufsiz=81920) at http_filters.c:1540 1540 if (r->remaining < 0 || (!r->read_chunked && r->remaining == 0)) { (gdb) n 1544 bb = apr_brigade_create(r->pool, r->connection->bucket_alloc); (gdb) 1545 if (bb == NULL) { (gdb) 1544 bb = apr_brigade_create(r->pool, r->connection->bucket_alloc); (gdb) 1545 if (bb == NULL) { 

----- line 1544.1545 is not in any loop, but they are repeated. Can someone enlighten me?

Answer 1

What level of optimization did you have when you compiled this?

Even a minimal level of optimization can cause your debugger to move along the source lines, as crazy as the built-in compiler, reorders and generally plays with your code.