It's too far-fetched for my tastes. I think gcc should not do it.
How gcc can know what printf() and puts() mean in *my* libc?
Well, that's what -fno-builtin is for.
More precisely, -ffreestanding.
I think such optimizations should be done in glibc.
The point is that you can't. GCC knows if an argument is a string
literal
... not only because of that. The point is that only a compiler can
parse the format string upfront. GCC can look at the format string of this
char *x;
...
printf ("foo %s bar", x);
and compile it as
fp = stdout;
fputs ("foo ", fp);
fputs (x, fp);
fputs (" bar", fp);
while glibc must obviously parse the format string at run-time (which is
the main source of overhead).
sprintf(dest, "%dconstant%...", args1, args...) -> sprintf(dest, "%d",
args1); memcpy(dest+X, "constant", 8); sprintf(dest+XX, "%...", args...);
How do you know that in this place user wants faster, not smaller code?
I suppose we would only do the transformations that have a speed-space
tradeoff with -O3, and not with -Os.
You could also make it profile-driven.
Paolo
