On 10/17/2011 01:51 PM, Richard Guenther wrote:
> On Sun, Oct 16, 2011 at 12:05 PM, Tom de Vries <[email protected]> wrote:
>> On 10/14/2011 12:00 PM, Richard Guenther wrote:
>>> On Fri, Oct 14, 2011 at 1:12 AM, Tom de Vries <[email protected]>
>>> wrote:
>>>> On 10/12/2011 02:19 PM, Richard Guenther wrote:
>>>>> On Wed, Oct 12, 2011 at 8:35 AM, Tom de Vries <[email protected]>
>>>>> wrote:
>>>>>> Richard,
>>>>>>
>>>>>> I have a patch for PR50672.
>>>>>>
>>>>>> When compiling the testcase from the PR with -ftree-tail-merge, the
>>>>>> scenario is
>>>>>> as follows:
>>>>>>
>>>>>> We start out tail_merge_optimize with blocks 14 and 20, which are alike,
>>>>>> but not
>>>>>> equal, since they have different successors:
>>>>>> ...
>>>>>> # BLOCK 14 freq:690
>>>>>> # PRED: 25 [61.0%] (false,exec)
>>>>>>
>>>>>> if (wD.2197_57(D) != 0B)
>>>>>> goto <bb 15>;
>>>>>> else
>>>>>> goto <bb 16>;
>>>>>> # SUCC: 15 [78.4%] (true,exec) 16 [21.6%] (false,exec)
>>>>>>
>>>>>>
>>>>>> # BLOCK 20 freq:2900
>>>>>> # PRED: 29 [100.0%] (fallthru) 31 [100.0%] (fallthru)
>>>>>>
>>>>>> # .MEMD.2447_209 = PHI <.MEMD.2447_125(29), .MEMD.2447_129(31)>
>>>>>> if (wD.2197_57(D) != 0B)
>>>>>> goto <bb 5>;
>>>>>> else
>>>>>> goto <bb 6>;
>>>>>> # SUCC: 5 [85.0%] (true,exec) 6 [15.0%] (false,exec)
>>>>>> ...
>>>>>>
>>>>>> In the first iteration, we merge block 5 with block 15 and block 6 with
>>>>>> block
>>>>>> 16. After that, the blocks 14 and 20 are equal.
>>>>>>
>>>>>> In the second iteration, the blocks 14 and 20 are merged, by redirecting
>>>>>> the
>>>>>> incoming edges of block 20 to block 14, and removing block 20.
>>>>>>
>>>>>> Block 20 also contains the definition of .MEMD.2447_209. Removing the
>>>>>> definition
>>>>>> delinks the vuse of .MEMD.2447_209 in block 5:
>>>>>> ...
>>>>>> # BLOCK 5 freq:6036
>>>>>> # PRED: 20 [85.0%] (true,exec)
>>>>>>
>>>>>> # PT = nonlocal escaped
>>>>>> D.2306_58 = &thisD.2200_10(D)->D.2156;
>>>>>> # .MEMD.2447_132 = VDEF <.MEMD.2447_209>
>>>>>> # USE = anything
>>>>>> # CLB = anything
>>>>>> drawLineD.2135 (D.2306_58, wD.2197_57(D), gcD.2198_59(D));
>>>>>> goto <bb 17>;
>>>>>> # SUCC: 17 [100.0%] (fallthru,exec)
>>>>>> ...
>>>>>
>>>>> And block 5 is retained and block 15 is discarded?
>>>>>
>>>>
>>>> Indeed.
>>>>
>>>>>> After the pass, when executing the TODO_update_ssa_only_virtuals, we
>>>>>> update the
>>>>>> drawLine call in block 5 using rewrite_update_stmt, which calls
>>>>>> maybe_replace_use for the vuse operand.
>>>>>>
>>>>>> However, maybe_replace_use doesn't have an effect since the old vuse and
>>>>>> the new
>>>>>> vuse happen to be the same (rdef == use), so SET_USE is not called and
>>>>>> the vuse
>>>>>> remains delinked:
>>>>>> ...
>>>>>> if (rdef && rdef != use)
>>>>>> SET_USE (use_p, rdef);
>>>>>> ...
>>>>>>
>>>>>> The patch fixes this by forcing SET_USE for delinked uses.
>>>>>
>>>>> That isn't the correct fix. Whoever unlinks the vuse (by removing its
>>>>> definition) has to replace it with something valid, which is either the
>>>>> bare symbol .MEM, or the VUSE associated with the removed VDEF
>>>>> (thus, as unlink_stmt_vdef does).
>>>>>
>>>>
>>>> Another try. For each deleted bb, we call unlink_stmt_vdef for the
>>>> statements,
>>>> and replace the .MEM phi uses with the bare .MEM symbol.
>>>>
>>>> Bootstrapped and reg-tested on x86_64.
>>>>
>>>> Ok for trunk?
>>>
>>> Better. For
>>>
>>> +
>>> + FOR_EACH_IMM_USE_STMT (use_stmt, iter, res)
>>> + {
>>> + FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
>>> + SET_USE (use_p, SSA_NAME_VAR (res));
>>> + }
>>>
>>> you can use mark_virtual_phi_result_for_renaming (phi) instead.
>>>
>>> + for (i = gsi_last_bb (bb); !gsi_end_p (i); gsi_prev_nondebug (&i))
>>> + unlink_stmt_vdef (gsi_stmt (i));
>>>
>>> is that actually necessary? That is, isn't the block that follows a
>>> deleted block always starting with a virtual PHI?
>>
>> Block 20 is deleted. Block 5 follows the deleted block 20. Block 5 does not
>> start with a virtual PHI.
>>
>>> If not it should
>>> be enough to walk to the first stmt that uses a virtual operand
>>> and similar to the PHI case replace all its uses with the bare
>>> symbol.
>>
>> I think we need to handle the exposed uses (meaning outside the block) of
>> vdefs
>> in each deleted block. The only vdef that can have exposed uses is the last
>> vdef
>> in the block. So we should find the last vdef (gimple with gimple_vdef or
>> virtual PHI) and handle the related uses.
>>
>> Bootstrapped and regtested on x86_64. OK for trunk?
>
> Hmmm. I can see that this will fail when the block has a store
> but not a virtual PHI node, thus, when renaming does not reach
> a bare .MEM symbol walking the use-def chain from the VUSE
> of the store. What release_last_vdef should do is trigger a rename
> of subsequent VUSEs in successors of the deleted block. Which
> requires you to do something like
>
> static void
> rename_last_vdef (basic_block bb)
> {
> + gimple_stmt_iterator i;
> +
> + for (i = gsi_last_bb (bb); !gsi_end_p (i); gsi_prev_nondebug (&i))
> + {
> + gimple stmt = gsi_stmt (i);
> + if (gimple_vdef (stmt) == NULL_TREE)
> + continue;
> +
> + mark_virtual_operand_for_renaming (gimple_vdef (stmt));
> return;
> }
>
> + for (i = gsi_start_phis (bb); !gsi_end_p (i); gsi_next (&i))
> + {
> + gimple phi = gsi_stmt (i);
> + tree res = gimple_phi_result (phi);
> +
> + if (is_gimple_reg (res))
> + continue;
> +
> + mark_virtual_phi_result_for_renaming (phi);
> + return;
> + }
> }
>
> And split out the
>
> result_var = SSA_NAME_VAR (result_ssa);
> FOR_EACH_IMM_USE_STMT (stmt, iter, result_ssa)
> {
> FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
> SET_USE (use_p, result_var);
> update_stmt (stmt);
> used = true;
> }
> if (used)
> mark_sym_for_renaming (result_var);
>
> part of mark_virtual_phi_result_for_renaming into the new function
> mark_virtual_operand_for_renaming (basically rename it and
> make mark_virtual_phi_result_for_renaming a wrapper around it,
> passing gimple_phi_result).
>
> Ok with a change as suggested above.
>
Retested on x86_64 and committed.
Thanks,
- Tom
> Thanks,
> Richard.
>
2011-10-18 Tom de Vries <[email protected]>
PR tree-optimization/50672
* tree-ssa-dce.c (mark_virtual_operand_for_renaming): New function,
factored out of ...
(mark_virtual_phi_result_for_renaming): Use
mark_virtual_operand_for_renaming.
* tree-flow.h (mark_virtual_operand_for_renaming): Declare.
* tree-ssa-tail-merge.c (release_last_vdef): New function.
(purge_bbs): Add update_vops parameter. Call release_last_vdef for each
deleted basic block.
(tail_merge_optimize): Add argument to call to purge_bbs.
Index: gcc/tree-ssa-tail-merge.c
===================================================================
--- gcc/tree-ssa-tail-merge.c (revision 179773)
+++ gcc/tree-ssa-tail-merge.c (working copy)
@@ -773,18 +773,56 @@ same_succ_flush_bbs (bitmap bbs)
}
}
+/* Release the last vdef in BB, either normal or phi result. */
+
+static void
+release_last_vdef (basic_block bb)
+{
+ gimple_stmt_iterator i;
+
+ for (i = gsi_last_bb (bb); !gsi_end_p (i); gsi_prev_nondebug (&i))
+ {
+ gimple stmt = gsi_stmt (i);
+ if (gimple_vdef (stmt) == NULL_TREE)
+ continue;
+
+ mark_virtual_operand_for_renaming (gimple_vdef (stmt));
+ return;
+ }
+
+ for (i = gsi_start_phis (bb); !gsi_end_p (i); gsi_next (&i))
+ {
+ gimple phi = gsi_stmt (i);
+ tree res = gimple_phi_result (phi);
+
+ if (is_gimple_reg (res))
+ continue;
+
+ mark_virtual_phi_result_for_renaming (phi);
+ return;
+ }
+
+}
+
/* Delete all deleted_bbs. */
static void
-purge_bbs (void)
+purge_bbs (bool update_vops)
{
unsigned int i;
bitmap_iterator bi;
+ basic_block bb;
same_succ_flush_bbs (deleted_bbs);
EXECUTE_IF_SET_IN_BITMAP (deleted_bbs, 0, i, bi)
- delete_basic_block (BASIC_BLOCK (i));
+ {
+ bb = BASIC_BLOCK (i);
+ if (!update_vops)
+ release_last_vdef (bb);
+
+ delete_basic_block (bb);
+ }
bitmap_and_compl_into (deleted_bb_preds, deleted_bbs);
bitmap_clear (deleted_bbs);
@@ -1665,7 +1703,7 @@ tail_merge_optimize (unsigned int todo)
break;
free_dominance_info (CDI_DOMINATORS);
- purge_bbs ();
+ purge_bbs (update_vops);
if (iteration_nr == max_iterations)
break;
Index: gcc/tree-ssa-dce.c
===================================================================
--- gcc/tree-ssa-dce.c (revision 179773)
+++ gcc/tree-ssa-dce.c (working copy)
@@ -982,18 +982,36 @@ propagate_necessity (struct edge_list *e
}
}
-/* Replace all uses of result of PHI by underlying variable and mark it
+/* Replace all uses of NAME by underlying variable and mark it
for renaming. */
void
-mark_virtual_phi_result_for_renaming (gimple phi)
+mark_virtual_operand_for_renaming (tree name)
{
bool used = false;
imm_use_iterator iter;
use_operand_p use_p;
gimple stmt;
- tree result_ssa, result_var;
+ tree name_var;
+
+ name_var = SSA_NAME_VAR (name);
+ FOR_EACH_IMM_USE_STMT (stmt, iter, name)
+ {
+ FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
+ SET_USE (use_p, name_var);
+ update_stmt (stmt);
+ used = true;
+ }
+ if (used)
+ mark_sym_for_renaming (name_var);
+}
+/* Replace all uses of result of PHI by underlying variable and mark it
+ for renaming. */
+
+void
+mark_virtual_phi_result_for_renaming (gimple phi)
+{
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file, "Marking result for renaming : ");
@@ -1001,19 +1019,10 @@ mark_virtual_phi_result_for_renaming (gi
fprintf (dump_file, "\n");
}
- result_ssa = gimple_phi_result (phi);
- result_var = SSA_NAME_VAR (result_ssa);
- FOR_EACH_IMM_USE_STMT (stmt, iter, result_ssa)
- {
- FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
- SET_USE (use_p, result_var);
- update_stmt (stmt);
- used = true;
- }
- if (used)
- mark_sym_for_renaming (result_var);
+ mark_virtual_operand_for_renaming (gimple_phi_result (phi));
}
+
/* Remove dead PHI nodes from block BB. */
static bool
Index: gcc/tree-flow.h
===================================================================
--- gcc/tree-flow.h (revision 179773)
+++ gcc/tree-flow.h (working copy)
@@ -715,6 +715,7 @@ bool stmt_dominates_stmt_p (gimple, gimp
void mark_virtual_ops_for_renaming (gimple);
/* In tree-ssa-dce.c */
+void mark_virtual_operand_for_renaming (tree);
void mark_virtual_phi_result_for_renaming (gimple);
/* In tree-ssa-threadedge.c */
