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Postings from July 2014
Since jhi is offline on IRC ATM, this is a ML message. Things like memcmp, strlen, memset, memcpy can be inlined, there are dedicated x86 instructions which literally are those 4 functions in 4 x86 opcode, read Visual C's inlining doc for ideas on things that are often inlined http://msdn.microsoft.com/en-us/library/tzkfha43.aspx . There is no reliable way to know if they will or won't be inlined. UNLIKELY() or PGO can cause certain code blocks to be small (-Os, calls c lib func or inline version, depending on how many bytes of instructions it takes to do either) or fast (inlining time, or C lib call). Since on some CPUs, the fancy "string" instructions ( http://www.plantation-productions.com/Webster/www.artofasm.com/Linux/HTML/StringInstructions.html ) are implemented in microcode as "backwards compatibility", and are slower than the longer in machine code bytes "modern" implementations that use "modern" instructions to the do same thing. Therefore some C compilers will always call the dedicated C functions, and not the inlined versions. Of course some compilers could also inline the long "modern" version of those functions. The other design issue is, should something like memcpy be replaceable through the PLT on ELF platforms? Maybe you want to print a message to STDERR if the memcpy length is over 1 MB for example. If memcpy was inlined, now your C compiler is "broken" and isn't POSIX compatible.