diff mbox

[2/2] shrink wrap a function with a single loop: split live_edge

Message ID CACgzC7BJCot4jY=TrfP9NzHh7SLq2g_bNeZaXSTkzwMnesaXRg@mail.gmail.com
State New
Headers show

Commit Message

Zhenqiang Chen May 13, 2014, 9:49 a.m. UTC 
On 9 May 2014 14:08, Jeff Law <law@redhat.com> wrote:
> On 05/08/14 02:07, Zhenqiang Chen wrote:
>>
>> Hi,
>>
>> The patch splits the live_edge for move_insn_for_shrink_wrap to sink
>> the copy out of the entry block.
>>
>> Bootstrap and no make check regression on X86-64 and ARM.
>>
>> OK for trunk?
>>
>> Thanks!
>> -Zhenqiang
>>
>> ChangeLog:
>> 2014-05-08  Zhenqiang Chen  <zhenqiang.chen@linaro.org>
>>
>>          * function.c (next_block_for_reg): Allow live_edge->dest has two
>>          predecessors.
>>          (move_insn_for_shrink_wrap): Split live_edge.
>>          (prepre_shrink_wrap): One more parameter for
>> move_insn_for_shrink_wrap.
>>
>>
>> diff --git a/gcc/function.c b/gcc/function.c
>> index 764ac82..0be58e2 100644
>> --- a/gcc/function.c
>> +++ b/gcc/function.c
>> @@ -5381,7 +5381,7 @@ requires_stack_frame_p (rtx insn, HARD_REG_SET
>> prologue_used,
>>      and if BB is its only predecessor.  Return that block if so,
>>      otherwise return null.  */
>>
>> -static basic_block
>> +static edge
>>   next_block_for_reg (basic_block bb, int regno, int end_regno)
>
> Comment for this function needs to be changed.  You're no longer returning a
> block, but the edge leading to the block.  It also seems the name of the
> function ought to change.

The comment and function name are updated.

> This looks basically OK.  I'd like to see the requested cleanups made, then
> the resulting new patch reposted for a final review.

Here is the updated patch based on the cleaned shrink-wrapping code:

ChangeLog:
2014-05-13  Zhenqiang Chen  <zhenqiang.chen@linaro.org>

        * shrink-wrap.c: Update comment.
        (next_block_for_reg): Rename to live_edge_for_reg.
        (live_edge_for_reg): Allow live_edge->dest has two predecessors.
        (move_insn_for_shrink_wrap): Split live_edge.
        (prepre_shrink_wrap): One more parameter for move_insn_for_shrink_wrap.

   edge_iterator ei;
@@ -148,25 +148,30 @@ next_block_for_reg (basic_block bb, int regno,
int end_regno)
   if (live_edge->flags & EDGE_ABNORMAL)
     return NULL;

-  if (EDGE_COUNT (live_edge->dest->preds) > 1)
+  /* When live_edge->dest->preds == 2, we can create a new block on
+     the edge to make it meet the requirement.  */
+  if (EDGE_COUNT (live_edge->dest->preds) > 2)
     return NULL;

-  return live_edge->dest;
+  return live_edge;
 }

 /* Try to move INSN from BB to a successor.  Return true on success.
    USES and DEFS are the set of registers that are used and defined
-   after INSN in BB.  */
+   after INSN in BB.  SPLIT_P indicates whether a live edge from BB
+   is splitted or not.  */

static bool
 move_insn_for_shrink_wrap (basic_block bb, rtx insn,
                           const HARD_REG_SET uses,
-                          const HARD_REG_SET defs)
+                          const HARD_REG_SET defs,
+                          bool *split_p)
 {
   rtx set, src, dest;
   bitmap live_out, live_in, bb_uses, bb_defs;
   unsigned int i, dregno, end_dregno, sregno, end_sregno;
   basic_block next_block;
+  edge live_edge;

   /* Look for a simple register copy.  */
   set = single_set (insn);
@@ -191,10 +196,24 @@ move_insn_for_shrink_wrap (basic_block bb, rtx insn,
     return false;

   /* See whether there is a successor block to which we could move INSN.  */
-  next_block = next_block_for_reg (bb, dregno, end_dregno);
-  if (!next_block)
+  live_edge = live_edge_for_reg (bb, dregno, end_dregno);
+  if (!live_edge)
     return false;

+  next_block = live_edge->dest;
+  /* Create a new basic block on the edge.  */
+  if (EDGE_COUNT (next_block->preds) == 2)
+    {
+      next_block = split_edge (live_edge);
+
+      bitmap_copy (df_get_live_in (next_block), df_get_live_out (bb));
+      df_set_bb_dirty (next_block);
+
+      /* We should not split more than once for a function.  */
+      gcc_assert (!(*split_p));
+      *split_p = true;
+    }
+
   /* At this point we are committed to moving INSN, but let's try to
      move it as far as we can.  */
   do
@@ -212,7 +231,9 @@ move_insn_for_shrink_wrap (basic_block bb, rtx insn,
        {
          for (i = dregno; i < end_dregno; i++)
            {
-             if (REGNO_REG_SET_P (bb_uses, i) || REGNO_REG_SET_P (bb_defs, i)
+             if (*split_p
+                 || REGNO_REG_SET_P (bb_uses, i)
+                 || REGNO_REG_SET_P (bb_defs, i)
                  || REGNO_REG_SET_P (&DF_LIVE_BB_INFO (bb)->gen, i))
                next_block = NULL;
              CLEAR_REGNO_REG_SET (live_out, i);
@@ -223,7 +244,8 @@ move_insn_for_shrink_wrap (basic_block bb, rtx insn,
             Either way, SRC is now live on entry.  */
          for (i = sregno; i < end_sregno; i++)
            {
-             if (REGNO_REG_SET_P (bb_defs, i)
+             if (*split_p
+                 || REGNO_REG_SET_P (bb_defs, i)
                  || REGNO_REG_SET_P (&DF_LIVE_BB_INFO (bb)->gen, i))
                next_block = NULL;
              SET_REGNO_REG_SET (live_out, i);
@@ -252,21 +274,31 @@ move_insn_for_shrink_wrap (basic_block bb, rtx insn,
       /* If we don't need to add the move to BB, look for a single
         successor block.  */
       if (next_block)
-       next_block = next_block_for_reg (next_block, dregno, end_dregno);
+       {
+         live_edge = live_edge_for_reg (next_block, dregno, end_dregno);
+         if (!live_edge || EDGE_COUNT (live_edge->dest->preds) > 1)
+           break;
+         next_block = live_edge->dest;
+       }
     }
   while (next_block);

-  /* BB now defines DEST.  It only uses the parts of DEST that overlap SRC
-     (next loop).  */
-  for (i = dregno; i < end_dregno; i++)
+  /* For the new created basic block, there is no dataflow info at all.
+     So skip the following dataflow update and check.  */
+  if (!(*split_p))
     {
-      CLEAR_REGNO_REG_SET (bb_uses, i);
-      SET_REGNO_REG_SET (bb_defs, i);
-    }
+      /* BB now defines DEST.  It only uses the parts of DEST that overlap SRC
+        (next loop).  */
+      for (i = dregno; i < end_dregno; i++)
+       {
+         CLEAR_REGNO_REG_SET (bb_uses, i);
+         SET_REGNO_REG_SET (bb_defs, i);
+       }

-  /* BB now uses SRC.  */
-  for (i = sregno; i < end_sregno; i++)
-    SET_REGNO_REG_SET (bb_uses, i);
+      /* BB now uses SRC.  */
+      for (i = sregno; i < end_sregno; i++)
+       SET_REGNO_REG_SET (bb_uses, i);
+    }

   emit_insn_after (PATTERN (insn), bb_note (bb));
   delete_insn (insn);
@@ -286,12 +318,14 @@ prepare_shrink_wrap (basic_block entry_block)
   rtx insn, curr, x;
   HARD_REG_SET uses, defs;
   df_ref *ref;
+  bool split_p = false;

   CLEAR_HARD_REG_SET (uses);
   CLEAR_HARD_REG_SET (defs);
   FOR_BB_INSNS_REVERSE_SAFE (entry_block, insn, curr)
     if (NONDEBUG_INSN_P (insn)
-       && !move_insn_for_shrink_wrap (entry_block, insn, uses, defs))
+       && !move_insn_for_shrink_wrap (entry_block, insn, uses, defs,
+                                      &split_p))
       {
        /* Add all defined registers to DEFs.  */
        for (ref = DF_INSN_DEFS (insn); *ref; ref++)

Comments

Jeff Law May 14, 2014, 6:03 p.m. UTC | #1 
On 05/13/14 03:49, Zhenqiang Chen wrote:
> On 9 May 2014 14:08, Jeff Law <law@redhat.com> wrote:
>> On 05/08/14 02:07, Zhenqiang Chen wrote:
>>>
>>> Hi,
>>>
>>> The patch splits the live_edge for move_insn_for_shrink_wrap to sink
>>> the copy out of the entry block.
>>>
>>> Bootstrap and no make check regression on X86-64 and ARM.
>>>
>>> OK for trunk?
>>>
>>> Thanks!
>>> -Zhenqiang
>>>
>>> ChangeLog:
>>> 2014-05-08  Zhenqiang Chen  <zhenqiang.chen@linaro.org>
>>>
>>>           * function.c (next_block_for_reg): Allow live_edge->dest has two
>>>           predecessors.
>>>           (move_insn_for_shrink_wrap): Split live_edge.
>>>           (prepre_shrink_wrap): One more parameter for
>>> move_insn_for_shrink_wrap.
OK.
jeff
diff mbox

Patch

diff --git a/gcc/shrink-wrap.c b/gcc/shrink-wrap.c
index b302777..f11e920 100644
--- a/gcc/shrink-wrap.c
+++ b/gcc/shrink-wrap.c
@@ -1,4 +1,4 @@ 
-/* Expands front end tree to back end RTL for GCC.
+/* Shrink-wrapping related optimizations.
    Copyright (C) 1987-2014 Free Software Foundation, Inc.

 This file is part of GCC.
@@ -110,12 +110,12 @@  requires_stack_frame_p (rtx insn, HARD_REG_SET
prologue_used,
   return false;
 }

-/* See whether BB has a single successor that uses [REGNO, END_REGNO),
-   and if BB is its only predecessor.  Return that block if so,
-   otherwise return null.  */
+/* See whether there has a single live edge from BB, which dest uses
+   [REGNO, END_REGNO).  Return the live edge if its dest bb has
+   one or two predecessors.  Otherwise return NULL.  */

-static basic_block
-next_block_for_reg (basic_block bb, int regno, int end_regno)
+static edge
+live_edge_for_reg (basic_block bb, int regno, int end_regno)
 {
   edge e, live_edge;