Re: [Tack-devel] Assembler and linker

[Sorav B. <sb...@ii...>]

Again, thanks a lot George and David for the detailed and helpful
responses!  Yes I was able to access the man page and it was helpful!

One more question:  as far as I can tell, the ACK implements and respects
the cdecl calling convention on the "linux386" machine, is that correct?
However I also see that ACK does not align the stack to a 16-byte boundary,
as required by the cdecl calling conventions on Linux (since GCC-4.5).  Is
there any documentation on the calling conventions supported/implemented?

Sorav

On Sat, Oct 29, 2022 at 8:26 AM George Koehler <ke...@gm...> wrote:

> On Sat, 29 Oct 2022 01:26:48 +0200
> David Given <dg...@co...> wrote:
>
> > The main optimiser is a tool called ego, which is described in detail in
> > the whitepaper here:  https://tack.sourceforge.net/olddocs.html Which
> > optimisations are invoked are described the man page for ack itself ('man
> > ack' from your command line, assuming it's been installed properly).
>
> 'man ack' describes the -O option and the PROGRAMS opt, ego, top.
>
> -O and -O0 are the same as -O1 (util/ack/main.c:218).  -O5 and higher
> are the same as -O04, which is almost the same as -O4, except for a
> quirk about "multiplication" (lib/fe/descr:197).  ack without -O
> disables top, but some code generators force opt to run, which makes
> some optimizations unless you "ack -Ropt-n" (-n in 'man em_opt').
>
> On Fri, 28 Oct 2022 23:01:52 +0530
> Sorav Bansal <sb...@ii...> wrote:
>
> > Does ACK support inter-procedural optimizations?
>
> ack -O4 enables IL, which might inline one procedure into another.
> I don't know any other optimization that crosses procedures.
>
> The ACK's old design prevents some optimizations.
> This C code can't put "char c;" in a register,
>
> $ cat simple.c
> #include <stdio.h>
> int main(int argc, char **argv) {
>   char x;
>   for (x = 1; x < argc; x++)
>     puts(argv[x]);
> }
> $ ack -mosxppc -O4 -c.so simple.c
>
> The only variables that can go in registers are integers or floats
> with a size of 1 or 2 words.  We have r30 = argv and r31 = argc, but
> the byte "char x;" is smaller than a word, so "char x;" gets stuck in
> memory.  "struct { int i; } s;" would also get stuck in memory.
>
> Each "for" iteration loads x with "lbz r4,-1(fp)" to do argv[x]; then
> a 2nd load "lbz r4,-1(fp)" and a store "stb r1,-1(fp)" to do x++; then
> a 3rd load "lbz r4,-1(fp)" to check x < argc.  If we change "char x;"
> to "int x;", then these 3 loads and 1 store disappear.
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