On Wed, 5 Aug 2015, Tom de Vries wrote:
> On 05/08/15 09:29, Richard Biener wrote:
> > > This patch fixes that by making sure we reset the def stmt to NULL. This
> > > means
> > > >we can simplify release_dangling_ssa_names to just test for NULL def
> > > stmts.
> > Not sure if I understand the problem correctly but why are you not simply
> > releasing the SSA name when you remove its definition?
>
> In move_sese_region_to_fn we move a region of blocks from one function to
> another, bit by bit.
>
> When we encounter an ssa_name as def or use in the region, we:
> - generate a new ssa_name,
> - set the def stmt of the old name as def stmt of the new name, and
> - add a mapping from the old to the new name.
> The next time we encounter the same ssa_name in another statement, we find it
> in the map.
>
> If we release the old ssa name, we effectively create statements with operands
> in the free-list. The first point where that cause breakage, is in
> walk_gimple_op, which expects the TREE_TYPE of the lhs of an assign to be
> defined, which is not the case if it's in the free-list:
> ...
> case GIMPLE_ASSIGN:
> /* Walk the RHS operands. If the LHS is of a non-renamable type or
> is a register variable, we may use a COMPONENT_REF on the RHS.*/
> if (wi)
> {
> tree lhs = gimple_assign_lhs (stmt);
> wi->val_only
> = (is_gimple_reg_type (TREE_TYPE (lhs)) && !is_gimple_reg (lhs))
> || gimple_assign_rhs_class (stmt) != GIMPLE_SINGLE_RHS;
> }
> ...
Hmm, ok, probably because the stmt moving doesn't happen in DOM
order (move defs before uses). But
+
+ if (!SSA_NAME_IS_DEFAULT_DEF (name))
+ /* The statement has been moved to the child function. It no
longer
+ defines name in the original function. Mark the def stmt NULL,
and
+ let release_dangling_ssa_names deal with it. */
+ SSA_NAME_DEF_STMT (name) = NULL;
applies also to uses - I don't see why it couldn't happen that you
move a use but not its def (the def would be a parameter to the
split-out function). You'd wreck the IL of the source function this way.
I think that the whole dance of actually moving things instead of
just copying it isn't worth the extra maintainance (well, if we already
have a machinery duplicating a SESE region to another function - I
suppose gimple_duplicate_sese_region could be trivially changed to
support that).
Trunk doesn't have release_dangling_ssa_names it seems but I think
it belongs to move_sese_region_to_fn and not to omp-low.c and it
could also just walk the d->vars_map replace_ssa_name fills to
iterate over the removal candidates (and if the situation of
moving uses but not defs cannot happen you don't need any
SSA_NAME_DEF_STMT dance either).
Thanks,
Richard.
--
Richard Biener <rguent...@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Dilip Upmanyu, Graham
Norton, HRB 21284 (AG Nuernberg)
