On Tue, 2 Apr 2013, Jakub Jelinek wrote:
> Hi!
>
> Jason's http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34949#c12
> patch attempts to emit a clobber for *this at the end of the destructor,
> so that we can DSE stores into the object when the object is dead, but
> so far only VAR_DECLs have been allowed on the lhs of gimple_clobber_p
> stmts.
> This incremental patch allows there either a VAR_DECL, or MEM_REF.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Few comments below
> (Jason's patch can be just committed as the last thing in the series).
>
> 2013-04-02 Jakub Jelinek <ja...@redhat.com>
>
> PR c++/34949
> * tree-cfg.c (verify_gimple_assign_single): Allow lhs
> of gimple_clobber_p to be MEM_REF.
> * gimplify.c (gimplify_modify_expr): Gimplify *to_p of
> an assignment from TREE_CLOBBER_P. Allow it to be MEM_REF
> after gimplification.
> * asan.c (get_mem_ref_of_assignment): Don't instrument
> gimple_clobber_p stmts.
> * tree-ssa-dse.c (dse_optimize_stmt): Allow DSE of
> gimple_clobber_p stmt if they have MEM_REF lhs and
> are dead because of another gimple_clobber_p stmt.
> * tree-ssa-live.c (clear_unused_block_pointer): Treat
> gimple_clobber_p stmts like debug stmts.
> (remove_unused_locals): Remove clobbers with MEM_REF lhs
> that refer to unused VAR_DECLs or uninitialized values.
> * tree-sra.c (sra_ipa_reset_debug_stmts): Also remove
> gimple_clobber_p stmts if they refer to removed parameters.
> (get_repl_default_def_ssa_name, sra_ipa_modify_expr): Fix up
> formatting.
>
> --- gcc/tree-cfg.c.jj 2013-03-21 18:34:11.000000000 +0100
> +++ gcc/tree-cfg.c 2013-03-27 13:44:59.475007635 +0100
> @@ -3812,9 +3812,9 @@ verify_gimple_assign_single (gimple stmt
> }
>
> if (gimple_clobber_p (stmt)
> - && !DECL_P (lhs))
> + && !(DECL_P (lhs) || TREE_CODE (lhs) == MEM_REF))
> {
> - error ("non-decl LHS in clobber statement");
> + error ("non-decl/MEM_REF LHS in clobber statement");
> debug_generic_expr (lhs);
> return true;
> }
> --- gcc/gimplify.c.jj 2013-03-21 18:34:11.000000000 +0100
> +++ gcc/gimplify.c 2013-03-27 13:38:30.988181267 +0100
> @@ -4840,7 +4840,12 @@ gimplify_modify_expr (tree *expr_p, gimp
> so handle it here. */
> if (TREE_CLOBBER_P (*from_p))
> {
> - gcc_assert (!want_value && TREE_CODE (*to_p) == VAR_DECL);
> + ret = gimplify_expr (to_p, pre_p, post_p, is_gimple_lvalue, fb_lvalue);
> + if (ret == GS_ERROR)
> + return ret;
> + gcc_assert (!want_value
> + && (TREE_CODE (*to_p) == VAR_DECL
> + || TREE_CODE (*to_p) == MEM_REF));
> gimplify_seq_add_stmt (pre_p, gimple_build_assign (*to_p, *from_p));
> *expr_p = NULL;
> return GS_ALL_DONE;
> --- gcc/asan.c.jj 2013-02-28 22:22:03.000000000 +0100
> +++ gcc/asan.c 2013-03-27 14:29:54.531785577 +0100
> @@ -412,7 +412,8 @@ get_mem_ref_of_assignment (const gimple
> {
> gcc_assert (gimple_assign_single_p (assignment));
>
> - if (gimple_store_p (assignment))
> + if (gimple_store_p (assignment)
> + && !gimple_clobber_p (assignment))
hmm, maybe gimple_store_p should not consider a clobber a store?
> {
> ref->start = gimple_assign_lhs (assignment);
> *ref_is_store = true;
> --- gcc/tree-ssa-dse.c.jj 2013-01-11 09:02:37.000000000 +0100
> +++ gcc/tree-ssa-dse.c 2013-03-27 17:14:27.424466023 +0100
> @@ -218,7 +218,10 @@ dse_optimize_stmt (gimple_stmt_iterator
> if (is_gimple_call (stmt) && gimple_call_fndecl (stmt))
> return;
>
> - if (gimple_has_volatile_ops (stmt))
> + /* Don't return early on *this_2(D) ={v} {CLOBBER}. */
> + if (gimple_has_volatile_ops (stmt)
> + && (!gimple_clobber_p (stmt)
> + || TREE_CODE (gimple_assign_lhs (stmt)) != MEM_REF))
> return;
But this only means the clobber was not considered as "dead"
if there was a later store to the same location. So, why would
that change be needed?
> if (is_gimple_assign (stmt))
> @@ -228,6 +231,12 @@ dse_optimize_stmt (gimple_stmt_iterator
> if (!dse_possible_dead_store_p (stmt, &use_stmt))
> return;
>
> + /* But only remove *this_2(D) ={v} {CLOBBER} if killed by
> + another clobber stmt. */
> + if (gimple_clobber_p (stmt)
> + && !gimple_clobber_p (use_stmt))
> + return;
Ah. Hmm, can that ever happen? I presume the issue with non-decl
clobbers is that we will never remove them, even if the storage
becomes "dead"?
> /* If we have precisely one immediate use at this point and the
> stores are to the same memory location or there is a chain of
> virtual uses from stmt and the stmt which stores to that same
> --- gcc/tree-ssa-live.c.jj 2013-03-21 18:34:11.000000000 +0100
> +++ gcc/tree-ssa-live.c 2013-03-28 11:10:15.889669796 +0100
> @@ -623,8 +623,8 @@ clear_unused_block_pointer_1 (tree *tp,
> return NULL_TREE;
> }
>
> -/* Set all block pointer in debug stmt to NULL if the block is unused,
> - so that they will not be streamed out. */
> +/* Set all block pointer in debug or clobber stmt to NULL if the block
> + is unused, so that they will not be streamed out. */
>
> static void
> clear_unused_block_pointer (void)
> @@ -639,7 +639,7 @@ clear_unused_block_pointer (void)
> tree b;
> gimple stmt = gsi_stmt (gsi);
>
> - if (!is_gimple_debug (stmt))
> + if (!is_gimple_debug (stmt) && !gimple_clobber_p (stmt))
> continue;
> b = gimple_block (stmt);
> if (b && !TREE_USED (b))
> @@ -827,7 +827,26 @@ remove_unused_locals (void)
> if (gimple_clobber_p (stmt))
> {
> tree lhs = gimple_assign_lhs (stmt);
> + bool remove = false;
> + /* Remove clobbers referencing unused vars, or clobbers
> + with MEM_REF lhs referencing unused vars or uninitialized
> + pointers. */
> if (TREE_CODE (lhs) == VAR_DECL && !is_used_p (lhs))
> + remove = true;
> + else if (TREE_CODE (lhs) == MEM_REF)
> + {
> + ssa_op_iter iter;
> + tree op;
> + FOR_EACH_SSA_TREE_OPERAND (op, stmt, iter, SSA_OP_USE)
The only SSA use on a clobber stmt can possibly be TREE_OPERAND (lhs, 0)
when lhs is a MEM_REF, no need to use FOR_EACH_SSA_TREE_OPERAND.
So just
> + else if (TREE_CODE (lhs) == MEM_REF
&& TREE_CODE (TREE_OPERAND (lhs, 0)) == SSA_NAME)
...
> + if (SSA_NAME_VAR (op)
> + && TREE_CODE (SSA_NAME_VAR (op)) == VAR_DECL
> + && !is_used_p (SSA_NAME_VAR (op)))
> + remove = true;
I'm not sure this is really desired ... isn't a better check to do
has_single_use (op)? (which means it would be better suited to
be handled in DCE?)
Btw, due to propagation you can end up with MEM[&decl] = {CLOBBER};
which should be handled the same as the VAR_DECL case. Eventually
just use lhs = get_base_address (gimple_assign_lhs (stmt)) here.
> + else if (SSA_NAME_IS_DEFAULT_DEF (op)
> + && TREE_CODE (SSA_NAME_VAR (op)) != PARM_DECL)
> + remove = true;
> + }
> + if (remove)
> {
> unlink_stmt_vdef (stmt);
> gsi_remove (&gsi, true);
> --- gcc/tree-sra.c.jj 2013-03-21 18:34:11.000000000 +0100
> +++ gcc/tree-sra.c 2013-04-02 09:44:29.225462112 +0200
> @@ -2965,8 +2965,8 @@ sra_modify_constructor_assign (gimple *s
> static tree
> get_repl_default_def_ssa_name (struct access *racc)
> {
> - gcc_checking_assert (!racc->grp_to_be_replaced &&
> - !racc->grp_to_be_debug_replaced);
> + gcc_checking_assert (!racc->grp_to_be_replaced
> + && !racc->grp_to_be_debug_replaced);
> if (!racc->replacement_decl)
> racc->replacement_decl = create_access_replacement (racc);
> return get_or_create_ssa_default_def (cfun, racc->replacement_decl);
> @@ -4462,8 +4462,8 @@ sra_ipa_modify_expr (tree *expr, bool co
> {
> adj = &adjustments[i];
>
> - if (adj->base == base &&
> - (adj->offset == offset || adj->remove_param))
> + if (adj->base == base
> + && (adj->offset == offset || adj->remove_param))
> {
> cand = adj;
> break;
> @@ -4676,6 +4676,14 @@ sra_ipa_reset_debug_stmts (ipa_parm_adju
> if (name)
> FOR_EACH_IMM_USE_STMT (stmt, ui, name)
> {
> + if (gimple_clobber_p (stmt))
> + {
> + gimple_stmt_iterator cgsi = gsi_for_stmt (stmt);
> + unlink_stmt_vdef (stmt);
> + gsi_remove (&cgsi, true);
> + release_defs (stmt);
> + continue;
> + }
> /* All other users must have been removed by
> ipa_sra_modify_function_body. */
> gcc_assert (is_gimple_debug (stmt));
Otherwise the patch looks fine to me.
Thanks,
Richard.
