Optimizing with gcc

My notes while reading Optimizing applications with gcc & glibc by Ulrich Drepper.

• __extension__ to mark intentional use of GNU extension.
• poor mans 'lambda' (({ }))
• predicate to determine if parameter value is constant at runtime: __builtin_constant_p()
• mark pure functions with __attribute__((__const__))
• mark functions which never return with __attribute__((__noreturn__))
• __stdcall__ attribute on x86 makes callee correct the stack at ret, in Unix convention the caller corrects the stack
  
• mempcpy returns a pointer just after the last copied byte.
• calloc knows if memory is already full of 0's -> faster than malloc & memset
• int_least16_t, int_fast16_t when actual variable size is uninteresting, speed is
• replace stlen and + with strchr(s,'\0') or rawmemchr()
  
• gcc computed gotos and jump tables: && for the address of a label
• -pg and -profile : gprof and sprof