Re: [PATCH GCC]Rename and make remove_dead_inserted_code a simple dce interface

["Bin.Cheng" <amker.cheng@gmail.com>]

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On Wed, Nov 29, 2017 at 10:02 AM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Tue, Nov 28, 2017 at 3:48 PM, Bin Cheng <Bin.Cheng@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.cheng@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.

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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