[Libjit-developers] Register allocation bug

[Evin Robertson]

The program at the end of this email segfaults with libjit 0.0.4 using 
the x86 back-end.

The problem appears to be with register allocation.

The second to last line of procedure run is miscompiled.  It generates
a series of codes like:

40200206:       b9 c8 23 06 08          mov    $0x80623c8,%ecx
4020020b:       8b 4d e4                mov    0xffffffe4(%ebp),%ecx
4020020e:       89 09                   mov    %ecx,(%ecx)

It loads the address of a global into ecx, then loads the value of the
local variable into ecx as well.  It attempts the write, but the
destination address has been overwritten.

I don't understand the register allocation stuff well enough to repair 
the bug myself.


program tempcall;

Var a, b, c, d, e, f, g, h : Integer;

Procedure do_thing;
begin
   WriteLn(a, " ", c, " ", d);
end;

Procedure run;
Var as, bs, cs, ds, es, fs, gs, hs : Integer;
begin
   a := 1; b := 2; c := 3; d := 4; e := 5; f := 6; g := 7; h := 8;
   do_thing;
   as := a; bs := b; cs := c; ds := d; es := e; fs := f; gs := g; hs:=h;
   a := 0; b := 0; c := 0; d := 0; e := 0; f := 0; g := 0; h := 0;
   do_thing;
   a := as; b := bs; c := cs; d := ds; e := es; f := fs; g := gs; h:=hs;
   do_thing;
end;

begin
   run;
end.