[Bug rtl-optimization/31848] [4.3 regression] Invalid loop optimization causes bootstrap failure in genautomata

["rakdver at kam dot mff dot cuni dot cz" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #6 from rakdver at kam dot mff dot cuni dot cz  2007-05-10 09:42 -------
Subject: Re:  [4.3 regression] Invalid loop optimization causes bootstrap
failure in genautomata

> Now, imagine the representative of a class of invariant insns is this one:
> 
> (gdb) next
> 1161              reorder_insns (inv->insn, inv->insn, BB_END (preheader));
> (gdb) p debug_rtx(inv->insn)
> (insn 552 551 644 57 foo.c:11152 (set (reg:SI 323)
>         (reg/v/f:SI 170 [ compressed_min_issue_delay_vect ])) 161
> {*arm_movsi_insn} (nil)
>     (expr_list:REG_EQUAL (const_int 0 [0x0])
>         (nil)))
> $7 = void

The heuristics may need some tweaking... moving reg-reg moves out of
loop seems unnecessary.  Anyway,

> ...and we've moved the insn with note and all out of the loop, even though the
> note is not valid anymore.
> Index: loop-invariant.c
> ===================================================================
> --- loop-invariant.c    (revision 124576)
> +++ loop-invariant.c    (working copy)
> @@ -1156,9 +1156,21 @@ move_invariant_reg (struct loop *loop, u
>          to let emit_move_insn produce a valid instruction stream.  */
>        if (REG_P (dest) && !HARD_REGISTER_P (dest))
>         {
> +         rtx note;
> +
>           emit_insn_after (gen_move_insn (dest, reg), inv->insn);
>           SET_DEST (set) = reg;
>           reorder_insns (inv->insn, inv->insn, BB_END (preheader));
> +
> +         /* If there is a REG_EQUAL note on the insn we just moved, and
> +            insn is in a basic block that is not always executed, the note
> +            may no longer be valid after we move the insn.
> +            Note that uses in REG_EQUAL notes are taken into account in
> +            the computation of invariants.  Hence it is safe to retain the
> +            note even if the note contains register references.  */
> +         if (! inv->always_executed
> +             && (note = find_reg_note (inv->insn, REG_EQUAL, NULL_RTX)))
> +           remove_note (inv->insn, note);
>         }
>        else
>         {
> 
> 
> Zdenek, what do you think about this?

the patch looks OK.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31848