Hi Georg,
>This is a patch to test/review/comment on. It adds tail call
>optimization to avr backend.
>
>The implementation uses struct machine_function to pass information
>around, i.e. from avr_function_arg_advance to avr_function_ok_for_sibcall.
>
>Tail call support is more general than avr-ld's replacement of
>call/ret sequences with --relax which are sometimes wrong, see
>http://sourceware.org/PR12494
>
>gcc can, e.g. tail-call bar1 in
>
>void bar0 (void);
>void bar1 (int);
>
>int foo (int x)
>{
> bar0();
> return bar1 (x);
>}
To be on same page, can you explain how gcc optimizes above case? As I
understand, in a tail-call optimization, bar1 can return to the caller of
foo(). There can be different cases of handling this. But how is this handled
in gcc after recognizing that foo() is a candidate for tail call?
Also, I have applied the patch, and used it for a small test case as below:
int bar1(int x) {
x++;
return x;
}
int foo (int x)
{
return bar1 (x);
}
int main() {
volatile int i;
return foo(i);
}
avr-gcc -S -foptimize-sibling-calls tail-call.c
I find no difference in the code generated with and without tail call
optimization. (I am assuming -foptimize-sibling-calls should turn on this). Let
me know if I am doing something wrong.
Anitha
