GCC replaces calls with special parameters to some standard C functions to equivalent ones in order to increase performance. E.g. fputs with string parameter -> fwrite.
However, some of these calls take more instructions, which is not good if we optimize for size. These replacements should be avoided depending on the optimization switches. (See example below.)

Release:
gcc version 3.3 20030224 (prerelease)

Environment:
BUILD & HOST: Linux 2.4.20 i686 unknown
TARGET: arm-unknown-elf

How-To-Repeat:
This simple program demonstrates that fprintf is replaced by calling fwrite in the assembly output (arm-elf target with newlib library):

#include <stdio.h>
void foo ()
{
  fprintf(stderr, "Comment"); // fprintf->fwrite
}

ldr r3, .L2
ldr r3, [r3, #0]
ldr r0, .L2+4
ldr r3, [r3, #12]
mov r1, #1
mov r2, #7
b fwrite

However, calling fprintf would require two instructions less:

ldr r3, .L2
ldr r3, [r3, #0]
ldr r1, .L2+4
ldr r0, [r3, #12]
b fprintf