On Wed, Nov 29, 2017 at 10:02 AM, Richard Biener
<richard.guent...@gmail.com> wrote:
> On Tue, Nov 28, 2017 at 3:48 PM, Bin Cheng <bin.ch...@arm.com> wrote:
>> Hi,
>> This patch renames remove_dead_inserted_code to simple_dce_from_worklist,
>> moves it to tree-ssa-dce.c
>> and makes it a simple public DCE interface. Bootstrap and test along with
>> loop interchange. It's required
>> for interchange pass. Is it OK?
>
> + /* ??? Re-use seeds as worklist not only as initial set. This may end up
> + removing more code as well. If we keep seeds unchanged we could
> restrict
> + new worklist elements to members of seed. */
>
> Please remove this comment, while it applies to PRE when one takes
> remove_dead_inserted_code
> literally it doesn't apply to a seeded DCE.
>
> Please also rename 'seeds' to 'worklist' directly and document that
> worklist is consumed by the function.
> The function has linear complexity in the number of dead stmts, the
> constant factor is the number of
> SSA use operands in those stmts (so 2 on average I'd say).
>
> Ok with that change.
Updated, will commit new patch as attached.
Thanks,
bin
>
> Thanks,
> Richard.
>
>> BTW, I will push this along with interchange to branch:
>> gcc.gnu.org/svn/gcc/branches/gimple-linterchange.
>>
>> Thanks,
>> bin
>> 2017-11-27 Bin Cheng <bin.ch...@arm.com>
>>
>> * tree-ssa-dce.c (simple_dce_from_worklist): Move and rename from
>> tree-ssa-pre.c::remove_dead_inserted_code.
>> * tree-ssa-dce.h: New file.
>> * tree-ssa-pre.c (tree-ssa-dce.h): Include new header file.
>> (remove_dead_inserted_code): Move and rename to function
>> tree-ssa-dce.c::simple_dce_from_worklist.
>> (pass_pre::execute): Update use.
From 219f42625b89eb81e2beb6605c9d594e83ed5048 Mon Sep 17 00:00:00 2001
From: amker <amker@amker-laptop.(none)>
Date: Sun, 26 Nov 2017 20:56:19 +0800
Subject: [PATCH 01/41] simple-dce-interface
---
gcc/tree-ssa-dce.c | 52 ++++++++++++++++++++++++++++++++++++++++++
gcc/tree-ssa-dce.h | 22 ++++++++++++++++++
gcc/tree-ssa-pre.c | 67 +++++++-----------------------------------------------
3 files changed, 82 insertions(+), 59 deletions(-)
create mode 100644 gcc/tree-ssa-dce.h
diff --git a/gcc/tree-ssa-dce.c b/gcc/tree-ssa-dce.c
index a5f0edf..8595dec 100644
--- a/gcc/tree-ssa-dce.c
+++ b/gcc/tree-ssa-dce.c
@@ -1723,3 +1723,55 @@ make_pass_cd_dce (gcc::context *ctxt)
{
return new pass_cd_dce (ctxt);
}
+
+
+/* A cheap DCE interface. WORKLIST is a list of possibly dead stmts and
+ is consumed by this function. The function has linear complexity in
+ the number of dead stmts with a constant factor like the average SSA
+ use operands number. */
+
+void
+simple_dce_from_worklist (bitmap worklist)
+{
+ while (! bitmap_empty_p (worklist))
+ {
+ /* Pop item. */
+ unsigned i = bitmap_first_set_bit (worklist);
+ bitmap_clear_bit (worklist, i);
+
+ tree def = ssa_name (i);
+ /* Removed by somebody else or still in use. */
+ if (! def || ! has_zero_uses (def))
+ continue;
+
+ gimple *t = SSA_NAME_DEF_STMT (def);
+ if (gimple_has_side_effects (t))
+ continue;
+
+ /* Add uses to the worklist. */
+ ssa_op_iter iter;
+ use_operand_p use_p;
+ FOR_EACH_PHI_OR_STMT_USE (use_p, t, iter, SSA_OP_USE)
+ {
+ tree use = USE_FROM_PTR (use_p);
+ if (TREE_CODE (use) == SSA_NAME
+ && ! SSA_NAME_IS_DEFAULT_DEF (use))
+ bitmap_set_bit (worklist, SSA_NAME_VERSION (use));
+ }
+
+ /* Remove stmt. */
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, "Removing dead stmt:");
+ print_gimple_stmt (dump_file, t, 0);
+ }
+ gimple_stmt_iterator gsi = gsi_for_stmt (t);
+ if (gimple_code (t) == GIMPLE_PHI)
+ remove_phi_node (&gsi, true);
+ else
+ {
+ gsi_remove (&gsi, true);
+ release_defs (t);
+ }
+ }
+}
diff --git a/gcc/tree-ssa-dce.h b/gcc/tree-ssa-dce.h
new file mode 100644
index 0000000..2adb086
--- /dev/null
+++ b/gcc/tree-ssa-dce.h
@@ -0,0 +1,22 @@
+/* Copyright (C) 2017 Free Software Foundation, Inc.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it
+under the terms of the GNU General Public License as published by the
+Free Software Foundation; either version 3, or (at your option) any
+later version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT
+ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3. If not see
+<http://www.gnu.org/licenses/>. */
+
+#ifndef TREE_SSA_DCE_H
+#define TREE_SSA_DCE_H
+extern void simple_dce_from_worklist (bitmap);
+#endif
diff --git a/gcc/tree-ssa-pre.c b/gcc/tree-ssa-pre.c
index 281f100..c19d486 100644
--- a/gcc/tree-ssa-pre.c
+++ b/gcc/tree-ssa-pre.c
@@ -49,6 +49,7 @@ along with GCC; see the file COPYING3. If not see
#include "dbgcnt.h"
#include "domwalk.h"
#include "tree-ssa-propagate.h"
+#include "tree-ssa-dce.h"
#include "tree-cfgcleanup.h"
#include "alias.h"
@@ -4038,64 +4039,6 @@ compute_avail (void)
free (worklist);
}
-/* Cheap DCE of a known set of possibly dead stmts.
-
- Because we don't follow exactly the standard PRE algorithm, and decide not
- to insert PHI nodes sometimes, and because value numbering of casts isn't
- perfect, we sometimes end up inserting dead code. This simple DCE-like
- pass removes any insertions we made that weren't actually used. */
-
-static void
-remove_dead_inserted_code (void)
-{
- /* ??? Re-use inserted_exprs as worklist not only as initial set.
- This may end up removing non-inserted code as well. If we
- keep inserted_exprs unchanged we could restrict new worklist
- elements to members of inserted_exprs. */
- bitmap worklist = inserted_exprs;
- while (! bitmap_empty_p (worklist))
- {
- /* Pop item. */
- unsigned i = bitmap_first_set_bit (worklist);
- bitmap_clear_bit (worklist, i);
-
- tree def = ssa_name (i);
- /* Removed by somebody else or still in use. */
- if (! def || ! has_zero_uses (def))
- continue;
-
- gimple *t = SSA_NAME_DEF_STMT (def);
- if (gimple_has_side_effects (t))
- continue;
-
- /* Add uses to the worklist. */
- ssa_op_iter iter;
- use_operand_p use_p;
- FOR_EACH_PHI_OR_STMT_USE (use_p, t, iter, SSA_OP_USE)
- {
- tree use = USE_FROM_PTR (use_p);
- if (TREE_CODE (use) == SSA_NAME
- && ! SSA_NAME_IS_DEFAULT_DEF (use))
- bitmap_set_bit (worklist, SSA_NAME_VERSION (use));
- }
-
- /* Remove stmt. */
- if (dump_file && (dump_flags & TDF_DETAILS))
- {
- fprintf (dump_file, "Removing unnecessary insertion:");
- print_gimple_stmt (dump_file, t, 0);
- }
- gimple_stmt_iterator gsi = gsi_for_stmt (t);
- if (gimple_code (t) == GIMPLE_PHI)
- remove_phi_node (&gsi, true);
- else
- {
- gsi_remove (&gsi, true);
- release_defs (t);
- }
- }
-}
-
/* Initialize data structures used by PRE. */
@@ -4234,7 +4177,13 @@ pass_pre::execute (function *fun)
clear_expression_ids ();
scev_finalize ();
- remove_dead_inserted_code ();
+
+ /* Because we don't follow exactly the standard PRE algorithm, and decide not
+ to insert PHI nodes sometimes, and because value numbering of casts isn't
+ perfect, we sometimes end up inserting dead code. This simple DCE-like
+ pass removes any insertions we made that weren't actually used. */
+ simple_dce_from_worklist (inserted_exprs);
+
fini_pre ();
loop_optimizer_finalize ();
--
1.9.1
