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Re: [PATCH] Dissociate store_expr's temp from exp so that it is not marked as addressable
- From: Richard Guenther <rguenther at suse dot de>
- To: Martin Jambor <mjambor at suse dot cz>
- Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>, ebotcazou at adacore dot com
- Date: Mon, 2 Apr 2012 13:52:20 +0200 (CEST)
- Subject: Re: [PATCH] Dissociate store_expr's temp from exp so that it is not marked as addressable
- References: <20120329232205.GB2817@virgil.arch.suse.de> <Pine.LNX.firstname.lastname@example.org> <20120331070601.GA24942@virgil.arch.suse.de>
On Sat, 31 Mar 2012, Martin Jambor wrote:
> On Fri, Mar 30, 2012 at 10:03:59AM +0200, Richard Guenther wrote:
> > On Fri, 30 Mar 2012, Martin Jambor wrote:
> > > Hi,
> > >
> > > when testing a patch of mine on sparc64-linux, I came across an Ada
> > > bootstrap failure due to a structure DECL which was marked addressable
> > > but had a register DECL_RTL (and therefore mem_ref_refers_to_non_mem_p
> > > failed to trigger on it).
> > >
> > > Mode of the structure was TI (16 bytes int) and it was mistakenly
> > > marked as addressable during expansion of an assignment statement in
> > > which a 12 byte portion of it was copied to another structure with
> > > BLKmode. Specifically, this happened because expand_assignment called
> > > store_expr which loaded the required portion to temporary 12 byte
> > > BLKmode MEM_P variable and then called emit_block_move from the
> > > temporary to the destination. emit_block_move_hints then marked
> > > MEM_EXPR of the temp as addressable because it handled the copy by
> > > emitting a library call. And MEM_EXPR pointed to the DECL of the
> > > source of the assignment which I believe is the bug, thus this patch
> > > re-sets MEM_EXPR of temp in these cases.
> > >
> > > However, if anybody believes the main issue is elsewhere and another
> > > component of this chain of events needs to be fixed, I'll be happy to
> > > come up with another patch. so far this patch has passed bootstrap
> > > and testing on x86_64-linux and helped my patch which uncovered this
> > > issue to reach stage 3 of bootstrap.
> > >
> > > What do you think, is it OK for trunk?
> > Hmm, I think this should be done at the point we create the mem - where
> > does that happen?
> The function gets it by simply calling expand_expr_real:
> temp = expand_expr_real (exp, tmp_target, GET_MODE (target),
> ? EXPAND_STACK_PARM : EXPAND_NORMAL),
> I have reproduced the issue again and looked at how expand_expr_real_1
> comes up with the MEM attributes in the COMPONENT_REF case.
> The memory-backed temporary is created in:
> /* Otherwise, if this is a constant or the object is not in memory
> and need be, put it there. */
> else if (CONSTANT_P (op0) || (!MEM_P (op0) && must_force_mem))
> tree nt = build_qualified_type (TREE_TYPE (tem),
> (TYPE_QUALS (TREE_TYPE (tem))
> | TYPE_QUAL_CONST));
> memloc = assign_temp (nt, 1, 1, 1);
> emit_move_insn (memloc, op0);
> op0 = memloc;
> and at the end of the case, the bitpos is added by adjust_address,
> followed by set_mem_attributes (op0, exp, 0);
> Indeed it seems that we should not be calling set_mem_attributes if
> op0 is based on such temporary... or perhaps just make sure that we
> only clear MEM_EXPR afterwards?
Yes, either way I suppose. The following also looks dangerous to me:
/* If OFFSET is making OP0 more aligned than BIGGEST_ALIGNMENT,
record its alignment as BIGGEST_ALIGNMENT. */
if (MEM_P (op0) && bitpos == 0 && offset != 0
&& is_aligning_offset (offset, tem))
set_mem_align (op0, BIGGEST_ALIGNMENT);
Maybe we can fall through most of the rest of the function if we
canonicalized in the above way? Eric?