Re: prevent REG_EQUAL on set-mem insns

[Richard Guenther <richard dot guenther at gmail dot com>]

On Fri, Sep 10, 2010 at 6:26 PM, Olivier Hainque <hainque@adacore.com> wrote:
> Hello,
>
> At least a couple of spots in the middle end sometimes end up
> attaching a REG_EQUAL note to insns that don't set a REG.
>
> For example, we observe:
>
> ?(insn 7 6 61 2 q.adb:7 (set (mem/v:SI (reg/f:SI 124) [0 S4 A32])
> ? ? ? ?(reg:SI 125)) 325 {*movsi_internal1}
> ? ?(expr_list:REG_EQUAL (const_int 12 [0xc])
> ? ?...
>
> for the store from this Ada testcase:
>
> ? procedure q is
> ? ? x : integer;
> ? ? for x'address use system.null_address;
> ? begin
> ? ? x := 12;
> ? exception
> ? ? ?when others => null;
> ? end;
>
> out of fwprop1 on powerpc-aix with -O.
>
> This is invalid according to what rtl.texi clearly advertises:
>
> ?<< item REG_EQUIV
> ? ?@itemx REG_EQUAL
> ? ?This note is only valid on an insn that sets only one register and
> ? ?indicates that that register will be equal to @var{op} at run time;
> ? ?the scope of this equivalence differs between the two types of notes.
> ?>>
>
> And this becomes problematic when (for example) purge_dead_edges takes
> advantage of that definition, considering that insns with a (REG_EQUAL
> const) note cannot trap:
>
> ?/* If this instruction cannot trap, remove REG_EH_REGION notes. ?*/
> ?if (NONJUMP_INSN_P (insn)
> ? ? ?&& (note = find_reg_note (insn, REG_EH_REGION, NULL)))
> ? ?{
> ? ? ?rtx eqnote;
>
> ? ? ?if (! may_trap_p (PATTERN (insn))
> ? ? ? ? ?|| ((eqnote = find_reg_equal_equiv_note (insn))
> ? ? ? ? ? ? ?&& ! may_trap_p (XEXP (eqnote, 0))))
> ? ? ? ?remove_note (insn, note);
> ? ?}
>
> On the testcase at hand, this results in the removal of the insn
> quoted above from its EH region, eventhough that insn may (and does)
> trap at runtime.
>
> This is particularily visible here, because the insn happens to
> be the only insn in the region, and its removal results in the entire
> removal of the code expected to catch the Ada exception raised from
> the trap handler.
>
> The attached patch fixes this by preventing the invalid REG_EQUAL note
> attachement from a couple of places where we have witnessed it.
>
> This fixes the testcase on powerpc-aix and was successfully bootstrapped
> and regtested on x86_64-suse-linux.
>
> OK ?

Ok.

Thanks,
Richard.

> Thanks in advance,
>
> Olivier
>
> 2010-09-10 ?Olivier Hainque ?<hainque@adacore.com>
>
> ? ? ? ?* fwprop.c (forward_propagate_and_simplify): Only attach a
> ? ? ? ?REG_EQUAL note to an insn if the destination is a register.
> ? ? ? ?* gcse.c (try_replace_reg): Likewise.
>
> ? ? ? ?testsuite/
> ? ? ? ?* gnat.dg/memtrap.adb: New test.
>