Re: GCC Internals: built-in functions?

[Jonathan Wakely <jwakely.gcc@gmail.com>]

On 30 January 2011 20:45, Amittai Aviram wrote:
> On this GCC Internals page
>
> http://en.wikibooks.org/wiki/GNU_C_Compiler_Internals/GNU_C_Compiler_Architecture_3_4
>
> I found the following in the "GCC Initialization" section:
>
> "GCC built-in functions are the functions that are evaluated at compile time. For example, if the size argument of a strcpy() function is a constant then GCC replaces the function call with the required number of assignments."
>
> I was curious about this, so I tried compiling to assembly (-S) a very simple program:
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
>
> int main(void) {
>
>        char s1[0x10];
>        char * s0 = "HELLO";
>        strcpy(s1, s0);
>        printf("%s %s\n", s0, s1);
>        return EXIT_SUCCESS;
> }
>
> But the resulting assembly code simply calls strcpy with the two arguments, just as I would have expected had I not read the above sentence:
>
>        movq    $.LC0, -40(%rbp)
>        movq    -40(%rbp), %rdx
>        leaq    -32(%rbp), %rax
>        movq    %rdx, %rsi
>        movq    %rax, %rdi
>        call    strcpy
>
> (Here, .LC0 labels the string "HELLO".)
>
> So what does that sentence actually mean and what am I missing?  Thanks!

strcpy has no 'size' parameter, I assume it's meant to say strncpy