[PATCH] Fix PRs 66502 and 67167

[PATCH] Fix PRs 66502 and 67167

[Richard Biener]

Given there is now PR67167 I am going forward with the earlier posted
patch to switch SCCVN to PHI elimination in favor of another PHI
(to remove IVs) rather than in favor of its only executable edge value.

I still see no way to capture both cases without detecting the choice
and re-numbering the SCC twice, eventually choosing the "better" outcome.
And then the situation where both cases happen in the same SCC is not
handled either.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.

Richard.

2015-08-13  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/66502
	PR tree-optimization/67167
	* tree-ssa-sccvn.c (vn_phi_compute_hash): Do not include
	backedge arguments.
	(vn_phi_lookup): Adjust.
	(vn_phi_insert): Likewise.
	(visit_phi): Prefer to value-number to another PHI node
	over value-numbering to a PHI argument.
	(init_scc_vn): Mark DFS back edges.

	* gcc.dg/tree-ssa/ssa-fre-46.c: New testcase.

Index: gcc/tree-ssa-sccvn.c
===================================================================
--- gcc/tree-ssa-sccvn.c	(revision 226807)
+++ gcc/tree-ssa-sccvn.c	(working copy)
@@ -2655,17 +2655,24 @@ static inline hashval_t
 vn_phi_compute_hash (vn_phi_t vp1)
 {
   inchash::hash hstate (vp1->block->index);
-  int i;
   tree phi1op;
   tree type;
+  edge e;
+  edge_iterator ei;
 
   /* If all PHI arguments are constants we need to distinguish
      the PHI node via its type.  */
   type = vp1->type;
   hstate.merge_hash (vn_hash_type (type));
 
-  FOR_EACH_VEC_ELT (vp1->phiargs, i, phi1op)
+  FOR_EACH_EDGE (e, ei, vp1->block->preds)
     {
+      /* Don't hash backedge values they need to be handled as VN_TOP
+         for optimistic value-numbering.  */
+      if (e->flags & EDGE_DFS_BACK)
+	continue;
+
+      phi1op = vp1->phiargs[e->dest_idx];
       if (phi1op == VN_TOP)
 	continue;
       inchash::add_expr (phi1op, hstate);
@@ -2718,16 +2725,18 @@ vn_phi_lookup (gimple phi)
 {
   vn_phi_s **slot;
   struct vn_phi_s vp1;
-  unsigned i;
+  edge e;
+  edge_iterator ei;
 
   shared_lookup_phiargs.truncate (0);
+  shared_lookup_phiargs.safe_grow (gimple_phi_num_args (phi));
 
   /* Canonicalize the SSA_NAME's to their value number.  */
-  for (i = 0; i < gimple_phi_num_args (phi); i++)
+  FOR_EACH_EDGE (e, ei, gimple_bb (phi)->preds)
     {
-      tree def = PHI_ARG_DEF (phi, i);
+      tree def = PHI_ARG_DEF_FROM_EDGE (phi, e);
       def = TREE_CODE (def) == SSA_NAME ? SSA_VAL (def) : def;
-      shared_lookup_phiargs.safe_push (def);
+      shared_lookup_phiargs[e->dest_idx] = def;
     }
   vp1.type = TREE_TYPE (gimple_phi_result (phi));
   vp1.phiargs = shared_lookup_phiargs;
@@ -2751,15 +2760,18 @@ vn_phi_insert (gimple phi, tree result)
 {
   vn_phi_s **slot;
   vn_phi_t vp1 = current_info->phis_pool->allocate ();
-  unsigned i;
   vec<tree> args = vNULL;
+  edge e;
+  edge_iterator ei;
+
+  args.safe_grow (gimple_phi_num_args (phi));
 
   /* Canonicalize the SSA_NAME's to their value number.  */
-  for (i = 0; i < gimple_phi_num_args (phi); i++)
+  FOR_EACH_EDGE (e, ei, gimple_bb (phi)->preds)
     {
-      tree def = PHI_ARG_DEF (phi, i);
+      tree def = PHI_ARG_DEF_FROM_EDGE (phi, e);
       def = TREE_CODE (def) == SSA_NAME ? SSA_VAL (def) : def;
-      args.safe_push (def);
+      args[e->dest_idx] = def;
     }
   vp1->value_id = VN_INFO (result)->value_id;
   vp1->type = TREE_TYPE (gimple_phi_result (phi));
@@ -3244,28 +3256,23 @@ visit_phi (gimple phi)
 	if (def == VN_TOP)
 	  continue;
 	if (sameval == VN_TOP)
+	  sameval = def;
+	else if (!expressions_equal_p (def, sameval))
 	  {
-	    sameval = def;
-	  }
-	else
-	  {
-	    if (!expressions_equal_p (def, sameval))
-	      {
-		allsame = false;
-		break;
-	      }
+	    allsame = false;
+	    break;
 	  }
       }
 
-  /* If all value numbered to the same value, the phi node has that
-     value.  */
-  if (allsame)
-    return set_ssa_val_to (PHI_RESULT (phi), sameval);
-
-  /* Otherwise, see if it is equivalent to a phi node in this block.  */
+  /* First see if it is equivalent to a phi node in this block.  We prefer
+     this as it allows IV elimination - see PRs 66502 and 67167.  */
   result = vn_phi_lookup (phi);
   if (result)
     changed = set_ssa_val_to (PHI_RESULT (phi), result);
+  /* Otherwise all value numbered to the same value, the phi node has that
+     value.  */
+  else if (allsame)
+    changed = set_ssa_val_to (PHI_RESULT (phi), sameval);
   else
     {
       vn_phi_insert (phi, PHI_RESULT (phi));
@@ -4155,6 +4162,8 @@ init_scc_vn (void)
   int *rpo_numbers_temp;
 
   calculate_dominance_info (CDI_DOMINATORS);
+  mark_dfs_back_edges ();
+
   sccstack.create (0);
   constant_to_value_id = new hash_table<vn_constant_hasher> (23);
 
Index: gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-46.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-46.c	(revision 0)
+++ gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-46.c	(working copy)
@@ -0,0 +1,22 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-fre1-details" } */
+
+int x[1024];
+int foo (int a, int s, unsigned int k)
+{
+  int i = a, j = a;
+  int sum = 0;
+  do
+    {
+      sum += x[i];
+      sum += x[j];
+      i += s;
+      j += s;
+    }
+  while (k--);
+  return sum;
+}
+
+/* We want to remove the redundant induction variable and thus its PHI node.  */
+
+/* { dg-final { scan-tree-dump "Removing dead stmt \[^\r\n\]*PHI" "fre1" } } */

Re: [PATCH] Fix PRs 66502 and 67167

[Jiong Wang]

Richard Biener writes:

> Given there is now PR67167 I am going forward with the earlier posted
> patch to switch SCCVN to PHI elimination in favor of another PHI
> (to remove IVs) rather than in favor of its only executable edge value.
>
> I still see no way to capture both cases without detecting the choice
> and re-numbering the SCC twice, eventually choosing the "better" outcome.
> And then the situation where both cases happen in the same SCC is not
> handled either.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.
>
> Richard.
>
> 2015-08-13  Richard Biener  <rguenther@suse.de>
>
> 	PR tree-optimization/66502
> 	PR tree-optimization/67167
> 	* tree-ssa-sccvn.c (vn_phi_compute_hash): Do not include
> 	backedge arguments.
> 	(vn_phi_lookup): Adjust.
> 	(vn_phi_insert): Likewise.
> 	(visit_phi): Prefer to value-number to another PHI node
> 	over value-numbering to a PHI argument.
> 	(init_scc_vn): Mark DFS back edges.

Richard,

  I suspect this patch r226850 caused internal compiler error on
  ./gcc/testsuite/gcc.c-torture/compile/20121027-1.c on arm-non-eabi.
  The ICE gone away if I revert this patch.

  it can be easily reproduced by the following command. -mfpu and
  -mfloat are necessary.
  
  ./cc1 -O3 -nostdinc 20121027-1.c  -march=armv8-a -mthumb
  -mfpu=crypto-neon-fp-armv8 -mfloat-abi=hard

  cc1 is generated from
  
    ../gcc/configure --target=arm-none-eabi --enable-languages=c,c++

  do you mind to have a look?

  Thanks.
-- 
Regards,
Jiong

Re: [PATCH] Fix PRs 66502 and 67167

[Richard Biener]

On Fri, 21 Aug 2015, Jiong Wang wrote:

> 
> Richard Biener writes:
> 
> > Given there is now PR67167 I am going forward with the earlier posted
> > patch to switch SCCVN to PHI elimination in favor of another PHI
> > (to remove IVs) rather than in favor of its only executable edge value.
> >
> > I still see no way to capture both cases without detecting the choice
> > and re-numbering the SCC twice, eventually choosing the "better" outcome.
> > And then the situation where both cases happen in the same SCC is not
> > handled either.
> >
> > Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.
> >
> > Richard.
> >
> > 2015-08-13  Richard Biener  <rguenther@suse.de>
> >
> > 	PR tree-optimization/66502
> > 	PR tree-optimization/67167
> > 	* tree-ssa-sccvn.c (vn_phi_compute_hash): Do not include
> > 	backedge arguments.
> > 	(vn_phi_lookup): Adjust.
> > 	(vn_phi_insert): Likewise.
> > 	(visit_phi): Prefer to value-number to another PHI node
> > 	over value-numbering to a PHI argument.
> > 	(init_scc_vn): Mark DFS back edges.
> 
> Richard,
> 
>   I suspect this patch r226850 caused internal compiler error on
>   ./gcc/testsuite/gcc.c-torture/compile/20121027-1.c on arm-non-eabi.
>   The ICE gone away if I revert this patch.
> 
>   it can be easily reproduced by the following command. -mfpu and
>   -mfloat are necessary.
>   
>   ./cc1 -O3 -nostdinc 20121027-1.c  -march=armv8-a -mthumb
>   -mfpu=crypto-neon-fp-armv8 -mfloat-abi=hard
> 
>   cc1 is generated from
>   
>     ../gcc/configure --target=arm-none-eabi --enable-languages=c,c++
> 
>   do you mind to have a look?

I see the following ICE:

t.c:13:1: internal compiler error: in decompose_normal_address, at 
rtlanal.c:6090
 }
 ^
0xc94a37 decompose_normal_address
        /space/rguenther/tramp3d/trunk/gcc/rtlanal.c:6090
0xc94d25 decompose_address(address_info*, rtx_def**, machine_mode, 
unsigned char, rtx_code)
        /space/rguenther/tramp3d/trunk/gcc/rtlanal.c:6167
0xc94dc3 decompose_mem_address(address_info*, rtx_def*)
        /space/rguenther/tramp3d/trunk/gcc/rtlanal.c:6187
0xb61149 process_address_1
        /space/rguenther/tramp3d/trunk/gcc/lra-constraints.c:2867
0xb61c4e process_address
        /space/rguenther/tramp3d/trunk/gcc/lra-constraints.c:3124
0xb62607 curr_insn_transform
        /space/rguenther/tramp3d/trunk/gcc/lra-constraints.c:3419
0xb65250 lra_constraints(bool)
        /space/rguenther/tramp3d/trunk/gcc/lra-constraints.c:4421

that looks like a latent issue to me in an area of GCC I am not
familiar with.  I suggest to open a bugreport and CC Vladimir.

The r226850 change caused us to eliminate an induction variable
early (I suspect IVOPTs would have done this later anyway, but
I did not verify that):

Replaced redundant PHI node defining bl_2 with c_1
Replaced c_1 + 1 with bl_15 in all uses of c_16 = c_1 + 1;
Removing dead stmt c_16 = c_1 + 1;
Removing dead stmt bl_2 = PHI <0(2), bl_15(3)>

Thanks,
Richard.

>   Thanks.
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)

Re: [PATCH] Fix PRs 66502 and 67167

[Jiong Wang]

Richard Biener writes:

> I see the following ICE:
>
> t.c:13:1: internal compiler error: in decompose_normal_address, at 
> rtlanal.c:6090
>  }
>  ^
> 0xc94a37 decompose_normal_address
>         /space/rguenther/tramp3d/trunk/gcc/rtlanal.c:6090
> 0xc94d25 decompose_address(address_info*, rtx_def**, machine_mode, 
> unsigned char, rtx_code)
>         /space/rguenther/tramp3d/trunk/gcc/rtlanal.c:6167
> 0xc94dc3 decompose_mem_address(address_info*, rtx_def*)
>         /space/rguenther/tramp3d/trunk/gcc/rtlanal.c:6187
> 0xb61149 process_address_1
>         /space/rguenther/tramp3d/trunk/gcc/lra-constraints.c:2867
> 0xb61c4e process_address
>         /space/rguenther/tramp3d/trunk/gcc/lra-constraints.c:3124
> 0xb62607 curr_insn_transform
>         /space/rguenther/tramp3d/trunk/gcc/lra-constraints.c:3419
> 0xb65250 lra_constraints(bool)
>         /space/rguenther/tramp3d/trunk/gcc/lra-constraints.c:4421
>
> that looks like a latent issue to me in an area of GCC I am not
> familiar with.  I suggest to open a bugreport and CC Vladimir.

Thanks for the info. Done https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67305


>
> The r226850 change caused us to eliminate an induction variable
> early (I suspect IVOPTs would have done this later anyway, but
> I did not verify that):
>
> Replaced redundant PHI node defining bl_2 with c_1
> Replaced c_1 + 1 with bl_15 in all uses of c_16 = c_1 + 1;
> Removing dead stmt c_16 = c_1 + 1;
> Removing dead stmt bl_2 = PHI <0(2), bl_15(3)>
>
> Thanks,
> Richard.
>
>>   Thanks.
>> 

-- 
Regards,
Jiong

Re: Re: [PATCH] Fix PRs 66502 and 67167

[Jiong Wang]

On 21/08/15 10:47, Jiong Wang wrote:
> Richard Biener writes:
>
>> I see the following ICE:
>>
>> t.c:13:1: internal compiler error: in decompose_normal_address, at
>> rtlanal.c:6090
>>   }
>>   ^
>> 0xc94a37 decompose_normal_address
>>          /space/rguenther/tramp3d/trunk/gcc/rtlanal.c:6090
>> 0xc94d25 decompose_address(address_info*, rtx_def**, machine_mode,
>> unsigned char, rtx_code)
>>          /space/rguenther/tramp3d/trunk/gcc/rtlanal.c:6167
>> 0xc94dc3 decompose_mem_address(address_info*, rtx_def*)
>>          /space/rguenther/tramp3d/trunk/gcc/rtlanal.c:6187
>> 0xb61149 process_address_1
>>          /space/rguenther/tramp3d/trunk/gcc/lra-constraints.c:2867
>> 0xb61c4e process_address
>>          /space/rguenther/tramp3d/trunk/gcc/lra-constraints.c:3124
>> 0xb62607 curr_insn_transform
>>          /space/rguenther/tramp3d/trunk/gcc/lra-constraints.c:3419
>> 0xb65250 lra_constraints(bool)
>>          /space/rguenther/tramp3d/trunk/gcc/lra-constraints.c:4421
>>
>> that looks like a latent issue to me in an area of GCC I am not
>> familiar with.  I suggest to open a bugreport and CC Vladimir.
> Thanks for the info. Done https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67305

Richard,

   Though the ICE itself is caused by one latent bug in ARM backend 
(PR67305), while my
further double check shows there is performance regression since this 
patch. The regression
should have been caused by other gcc latent bugs in tree-vrp pass. 
Bugzilla created to track

   Thanks.

   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68234

Regards,
Jiong

>
>
>> The r226850 change caused us to eliminate an induction variable
>> early (I suspect IVOPTs would have done this later anyway, but
>> I did not verify that):
>>
>> Replaced redundant PHI node defining bl_2 with c_1
>> Replaced c_1 + 1 with bl_15 in all uses of c_16 = c_1 + 1;
>> Removing dead stmt c_16 = c_1 + 1;
>> Removing dead stmt bl_2 = PHI <0(2), bl_15(3)>
>>
>> Thanks,
>> Richard.
>>
>>>    Thanks.
>>>