[Qemu-devel] qemu branching internal questions

[Mike Frysinger]

i've been working on a new architecture port, but i cant quite figure
out some of the intricacies from reading the code.  i have all the
simple stuff working for linux-user (register moves, immediate moves,
loads, stores, syscall emulation) and want to move on to the next big
piece -- code flow changes.

i cant quite figure out the difference between DISAS_TB_JUMP and
DISAS_JUMP.  the exec-all.h header says one is for "only pc was
modified dynamically" while the other is "only pc was modified
statically".  is this referring to conditional vs unconditional jumps
?  or is this referring to direct vs indirect jumps ?
conditional: if cc jump 1f;
unconditional: jump 1f;
direct: jump foo;
indirect: P0 = [SP++]; jump (P0);

along these lines, when should i be using gen_new_label,
gen_set_label, tcg_gen_brcond*, and tcg_gen_setcond* ?  should they
only be used with conditional code ?  or should unconditional jumps be
generating labels too ?

for conditional register assignments, i think i should be using these
too.  so something like:
  if CC R0 = R1;
should turn into:
  l = gen_new_label();
  tcg_gen_brcondi_tl(TCG_COND_NE, cpu_cc, T, l);
  tcg_gen_mov_tl(reg_dst, reg_src);
  gen_set_label(l);
and i dont need to flag this bit of code as a jump (e.g. DISAS_JUMP) ...

also, having gone through the ops already available in tcg-op.h, ive
managed to decode what they do except for these:
tcg_gen_{ld,st}{8,16,32}{u,s}
i thought originally they were for handling load/store insns, but they
didnt work for me, and then i found the tcg_gen_qemu_{ld,st}* ops.  so
what is the point of these ones ?
-mike