Patchwork [tree-optimization] : Improve handling of conditional-branches on targets with high branch costs

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Submitter Kai Tietz
Date Oct. 10, 2011, 2:06 p.m.
Message ID <CAEwic4b04+W5H75cQFLGCO2FJuR73bPiH-F05HsZzamm2+RRzA@mail.gmail.com>
Download mbox | patch
Permalink /patch/118741/
State New
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Comments

Kai Tietz - Oct. 10, 2011, 2:06 p.m.
2011/10/10 Richard Guenther <richard.guenther@gmail.com>:
> On Mon, Oct 10, 2011 at 2:29 PM, Kai Tietz <ktietz70@googlemail.com> wrote:
>> Recent patch had a thinko on rhs of inner lhs check for TRUTH-IF.  It
>> has to be checked that the LHS code is same as outer CODE, as
>> otherwise we wouldn't apply different TRUTH-IF only on inner RHS of
>> LHS, which is of course wrong.
>>
>> Index: gcc/gcc/fold-const.c
>> ===================================================================
>> --- gcc.orig/gcc/fold-const.c
>> +++ gcc/gcc/fold-const.c
>> @@ -111,14 +111,13 @@ static tree decode_field_reference (loca
>>                                    tree *, tree *);
>>  static int all_ones_mask_p (const_tree, int);
>>  static tree sign_bit_p (tree, const_tree);
>> -static int simple_operand_p (const_tree);
>> +static int simple_operand_p (tree);
>>  static tree range_binop (enum tree_code, tree, tree, int, tree, int);
>>  static tree range_predecessor (tree);
>>  static tree range_successor (tree);
>>  static tree fold_range_test (location_t, enum tree_code, tree, tree, tree);
>>  static tree fold_cond_expr_with_comparison (location_t, tree, tree,
>> tree, tree);
>>  static tree unextend (tree, int, int, tree);
>> -static tree fold_truthop (location_t, enum tree_code, tree, tree, tree);
>>  static tree optimize_minmax_comparison (location_t, enum tree_code,
>>                                        tree, tree, tree);
>>  static tree extract_muldiv (tree, tree, enum tree_code, tree, bool *);
>> @@ -3500,7 +3499,7 @@ optimize_bit_field_compare (location_t l
>>   return lhs;
>>  }
>>
>> -/* Subroutine for fold_truthop: decode a field reference.
>> +/* Subroutine for fold_truth_andor_1: decode a field reference.
>>
>>    If EXP is a comparison reference, we return the innermost reference.
>>
>> @@ -3668,17 +3667,43 @@ sign_bit_p (tree exp, const_tree val)
>>   return NULL_TREE;
>>  }
>>
>> -/* Subroutine for fold_truthop: determine if an operand is simple enough
>> +/* Subroutine for fold_truth_andor_1: determine if an operand is simple enough
>>    to be evaluated unconditionally.  */
>>
>>  static int
>> -simple_operand_p (const_tree exp)
>> +simple_operand_p (tree exp)
>>  {
>> +  enum tree_code code;
>>   /* Strip any conversions that don't change the machine mode.  */
>>   STRIP_NOPS (exp);
>>
>> +  code = TREE_CODE (exp);
>> +
>> +  /* Handle some trivials   */
>> +  if (TREE_CODE_CLASS (code) == tcc_comparison)
>> +    return (tree_could_trap_p (exp)
>> +           && simple_operand_p (TREE_OPERAND (exp, 0))
>> +           && simple_operand_p (TREE_OPERAND (exp, 1)));
>
> And that's still wrong.
>
> Stopped reading here.
>
> Richard.

Oh, there is a not missing.  I didn't spot that, sorry.

To the point why we need to handle comparisons within simple_operand_p.

If we reject comparisons and logical not here, we won't have any
branching optimization anymore, as this the patch moves into
fold_truthandor.

The result with rejecting in simple_operand_p compares and logic-not
provides for the following example:

extern int doo (void);
extern int doo2 (void);

int foo (int a, int b, int c, int d, int e, int f)
{
  if (a && b && c && d && e && f)
    return doo ();
  return doo2 ();
}

we get the following gimple dump (-fdump-tree-gimple):

foo (int a, int b, int c, int d, int e, int f)
{
  int D.2752;

  if (a != 0) goto <D.2740>; else goto <D.2741>;
  <D.2740>:
  if (b != 0) goto <D.2742>; else goto <D.2743>;
  <D.2742>:
  if (c != 0) goto <D.2744>; else goto <D.2745>;
  <D.2744>:
  if (d != 0) goto <D.2746>; else goto <D.2747>;
  <D.2746>:
  if (e != 0) goto <D.2748>; else goto <D.2749>;
  <D.2748>:
  if (f != 0) goto <D.2750>; else goto <D.2751>;
  <D.2750>:
  D.2752 = doo ();
  return D.2752;
  <D.2751>:
  <D.2749>:
  <D.2747>:
  <D.2745>:
  <D.2743>:
  <D.2741>:
  D.2752 = doo2 ();
  return D.2752;
}

So this result is caused by the fact that a logical-and/or is always a
comparison.  As we are rejecting comparisons/logical-not,  we end up
with a sequence of TRUTH_(AND|OR)_IFs.  So the hole loop in
fold_truth_andor for trying to pack simple and side-effect-less
operands in tupels of two is useless.

For the new patch (attached with proper ! fix for compares) we get for
the same sample gimple output:

foo (int a, int b, int c, int d, int e, int f)
{
  _Bool D.2740;
  _Bool D.2741;
  _Bool D.2742;
  _Bool D.2745;
  _Bool D.2746;
  _Bool D.2747;
  _Bool D.2750;
  _Bool D.2751;
  _Bool D.2752;
  int D.2755;

  D.2740 = a != 0;
  D.2741 = b != 0;
  D.2742 = D.2740 & D.2741;
  if (D.2742 != 0) goto <D.2743>; else goto <D.2744>;
  <D.2743>:
  D.2745 = c != 0;
  D.2746 = d != 0;
  D.2747 = D.2745 & D.2746;
  if (D.2747 != 0) goto <D.2748>; else goto <D.2749>;
  <D.2748>:
  D.2750 = e != 0;
  D.2751 = f != 0;
  D.2752 = D.2750 & D.2751;
  if (D.2752 != 0) goto <D.2753>; else goto <D.2754>;
  <D.2753>:
  D.2755 = doo ();
  return D.2755;
  <D.2754>:
  <D.2749>:
  <D.2744>:
  D.2755 = doo2 ();
  return D.2755;
}

which is the proper output for high branching cost, as it tries to
avoid branches and not to tend them.

--
Kai

 static tree extract_muldiv (tree, tree, enum tree_code, tree, bool *);
@@ -3500,7 +3499,7 @@ optimize_bit_field_compare (location_t l
   return lhs;
 }
 
-/* Subroutine for fold_truthop: decode a field reference.
+/* Subroutine for fold_truth_andor_1: decode a field reference.

    If EXP is a comparison reference, we return the innermost reference.

@@ -3668,17 +3667,43 @@ sign_bit_p (tree exp, const_tree val)
   return NULL_TREE;
 }

-/* Subroutine for fold_truthop: determine if an operand is simple enough
+/* Subroutine for fold_truth_andor_1: determine if an operand is simple enough
    to be evaluated unconditionally.  */

 static int
-simple_operand_p (const_tree exp)
+simple_operand_p (tree exp)
 {
+  enum tree_code code;
   /* Strip any conversions that don't change the machine mode.  */
   STRIP_NOPS (exp);

+  code = TREE_CODE (exp);
+
+  /* Handle some trivials   */
+  if (TREE_CODE_CLASS (code) == tcc_comparison)
+    return (!tree_could_trap_p (exp)
+    	    && simple_operand_p (TREE_OPERAND (exp, 0))
+	    && simple_operand_p (TREE_OPERAND (exp, 1)));
+
+  if (FLOAT_TYPE_P (TREE_TYPE (exp))
+      && tree_could_trap_p (exp))
+    return false;
+
+  switch (code)
+    {
+    case SSA_NAME:
+      return true;
+    case TRUTH_NOT_EXPR:
+      return simple_operand_p (TREE_OPERAND (exp, 0));
+    case BIT_NOT_EXPR:
+      if (TREE_CODE (TREE_TYPE (exp)) != BOOLEAN_TYPE)
+        return false;
+      return simple_operand_p (TREE_OPERAND (exp, 0));
+    default:
+      break;
+    }
+
   return (CONSTANT_CLASS_P (exp)
-	  || TREE_CODE (exp) == SSA_NAME
 	  || (DECL_P (exp)
 	      && ! TREE_ADDRESSABLE (exp)
 	      && ! TREE_THIS_VOLATILE (exp)
@@ -4888,7 +4913,7 @@ fold_range_test (location_t loc, enum tr
   return 0;
 }
 
-/* Subroutine for fold_truthop: C is an INTEGER_CST interpreted as a P
+/* Subroutine for fold_truth_andor_1: C is an INTEGER_CST interpreted as a P
    bit value.  Arrange things so the extra bits will be set to zero if and
    only if C is signed-extended to its full width.  If MASK is nonzero,
    it is an INTEGER_CST that should be AND'ed with the extra bits.  */
@@ -5025,8 +5050,8 @@ merge_truthop_with_opposite_arm (locatio
    We return the simplified tree or 0 if no optimization is possible.  */

 static tree
-fold_truthop (location_t loc, enum tree_code code, tree truth_type,
-	      tree lhs, tree rhs)
+fold_truth_andor_1 (location_t loc, enum tree_code code, tree truth_type,
+		    tree lhs, tree rhs)
 {
   /* If this is the "or" of two comparisons, we can do something if
      the comparisons are NE_EXPR.  If this is the "and", we can do something
@@ -5054,8 +5079,6 @@ fold_truthop (location_t loc, enum tree_
   tree lntype, rntype, result;
   HOST_WIDE_INT first_bit, end_bit;
   int volatilep;
-  tree orig_lhs = lhs, orig_rhs = rhs;
-  enum tree_code orig_code = code;

   /* Start by getting the comparison codes.  Fail if anything is volatile.
      If one operand is a BIT_AND_EXPR with the constant one, treat it as if
@@ -5119,8 +5142,7 @@ fold_truthop (location_t loc, enum tree_
   /* If the RHS can be evaluated unconditionally and its operands are
      simple, it wins to evaluate the RHS unconditionally on machines
      with expensive branches.  In this case, this isn't a comparison
-     that can be merged.  Avoid doing this if the RHS is a floating-point
-     comparison since those can trap.  */
+     that can be merged.  */

   if (BRANCH_COST (optimize_function_for_speed_p (cfun),
 		   false) >= 2
@@ -5149,13 +5171,6 @@ fold_truthop (location_t loc, enum tree_
 			   build2 (BIT_IOR_EXPR, TREE_TYPE (ll_arg),
 				   ll_arg, rl_arg),
 			   build_int_cst (TREE_TYPE (ll_arg), 0));
-
-      if (LOGICAL_OP_NON_SHORT_CIRCUIT)
-	{
-	  if (code != orig_code || lhs != orig_lhs || rhs != orig_rhs)
-	    return build2_loc (loc, code, truth_type, lhs, rhs);
-	  return NULL_TREE;
-	}
     }

   /* See if the comparisons can be merged.  Then get all the parameters for
@@ -8380,13 +8395,46 @@ fold_truth_andor (location_t loc, enum t
      lhs is another similar operation, try to merge its rhs with our
      rhs.  Then try to merge our lhs and rhs.  */
   if (TREE_CODE (arg0) == code
-      && 0 != (tem = fold_truthop (loc, code, type,
-				   TREE_OPERAND (arg0, 1), arg1)))
+      && 0 != (tem = fold_truth_andor_1 (loc, code, type,
+					 TREE_OPERAND (arg0, 1), arg1)))
     return fold_build2_loc (loc, code, type, TREE_OPERAND (arg0, 0), tem);

-  if ((tem = fold_truthop (loc, code, type, arg0, arg1)) != 0)
+  if ((tem = fold_truth_andor_1 (loc, code, type, arg0, arg1)) != 0)
     return tem;

+  if ((code == TRUTH_ANDIF_EXPR || code == TRUTH_ORIF_EXPR)
+      && (BRANCH_COST (optimize_function_for_speed_p (cfun),
+		       false) >= 2)
+      && !TREE_SIDE_EFFECTS (arg1)
+      && LOGICAL_OP_NON_SHORT_CIRCUIT
+      && simple_operand_p (arg1))
+    {
+      enum tree_code ncode = (code == TRUTH_ANDIF_EXPR ? TRUTH_AND_EXPR
+						       : TRUTH_OR_EXPR);
+
+      /* We don't want to pack more then two leafs to an non-IF
+         If tree-code of left-hand operand isn't an AND/OR-IF code and not
+         equal to CODE, then we don't want to add right-hand operand.
+         If the inner right-hand side of left-hand operand has side-effects,
+         or isn't simple, then we can't add to it, as otherwise we might
+         destroy if-sequence.  */
+      if (TREE_CODE (arg0) == code
+      	  /* Needed for sequence points to handle trappings, and
+      	     side-effects.  */
+      	  && !TREE_SIDE_EFFECTS (TREE_OPERAND (arg0, 1))
+      	  && simple_operand_p (TREE_OPERAND (arg0, 1)))
+       {
+         tem = fold_build2_loc (loc, ncode, type, TREE_OPERAND (arg0, 1),
+				arg1);
+         return fold_build2_loc (loc, code, type, TREE_OPERAND (arg0, 0),
+				 tem);
+       }
+     /* Needed for sequence points to handle trappings, and side-effects.  */
+     else if (!TREE_SIDE_EFFECTS (arg0)
+	      && simple_operand_p (arg0))
+       return fold_build2_loc (loc, ncode, type, arg0, arg1);
+    }
+
   return NULL_TREE;
 }
Richard Guenther - Oct. 10, 2011, 2:58 p.m.
On Mon, Oct 10, 2011 at 4:06 PM, Kai Tietz <ktietz70@googlemail.com> wrote:
> 2011/10/10 Richard Guenther <richard.guenther@gmail.com>:
>> On Mon, Oct 10, 2011 at 2:29 PM, Kai Tietz <ktietz70@googlemail.com> wrote:
>>> Recent patch had a thinko on rhs of inner lhs check for TRUTH-IF.  It
>>> has to be checked that the LHS code is same as outer CODE, as
>>> otherwise we wouldn't apply different TRUTH-IF only on inner RHS of
>>> LHS, which is of course wrong.
>>>
>>> Index: gcc/gcc/fold-const.c
>>> ===================================================================
>>> --- gcc.orig/gcc/fold-const.c
>>> +++ gcc/gcc/fold-const.c
>>> @@ -111,14 +111,13 @@ static tree decode_field_reference (loca
>>>                                    tree *, tree *);
>>>  static int all_ones_mask_p (const_tree, int);
>>>  static tree sign_bit_p (tree, const_tree);
>>> -static int simple_operand_p (const_tree);
>>> +static int simple_operand_p (tree);
>>>  static tree range_binop (enum tree_code, tree, tree, int, tree, int);
>>>  static tree range_predecessor (tree);
>>>  static tree range_successor (tree);
>>>  static tree fold_range_test (location_t, enum tree_code, tree, tree, tree);
>>>  static tree fold_cond_expr_with_comparison (location_t, tree, tree,
>>> tree, tree);
>>>  static tree unextend (tree, int, int, tree);
>>> -static tree fold_truthop (location_t, enum tree_code, tree, tree, tree);
>>>  static tree optimize_minmax_comparison (location_t, enum tree_code,
>>>                                        tree, tree, tree);
>>>  static tree extract_muldiv (tree, tree, enum tree_code, tree, bool *);
>>> @@ -3500,7 +3499,7 @@ optimize_bit_field_compare (location_t l
>>>   return lhs;
>>>  }
>>>
>>> -/* Subroutine for fold_truthop: decode a field reference.
>>> +/* Subroutine for fold_truth_andor_1: decode a field reference.
>>>
>>>    If EXP is a comparison reference, we return the innermost reference.
>>>
>>> @@ -3668,17 +3667,43 @@ sign_bit_p (tree exp, const_tree val)
>>>   return NULL_TREE;
>>>  }
>>>
>>> -/* Subroutine for fold_truthop: determine if an operand is simple enough
>>> +/* Subroutine for fold_truth_andor_1: determine if an operand is simple enough
>>>    to be evaluated unconditionally.  */
>>>
>>>  static int
>>> -simple_operand_p (const_tree exp)
>>> +simple_operand_p (tree exp)
>>>  {
>>> +  enum tree_code code;
>>>   /* Strip any conversions that don't change the machine mode.  */
>>>   STRIP_NOPS (exp);
>>>
>>> +  code = TREE_CODE (exp);
>>> +
>>> +  /* Handle some trivials   */
>>> +  if (TREE_CODE_CLASS (code) == tcc_comparison)
>>> +    return (tree_could_trap_p (exp)
>>> +           && simple_operand_p (TREE_OPERAND (exp, 0))
>>> +           && simple_operand_p (TREE_OPERAND (exp, 1)));
>>
>> And that's still wrong.
>>
>> Stopped reading here.
>>
>> Richard.
>
> Oh, there is a not missing.  I didn't spot that, sorry.
>
> To the point why we need to handle comparisons within simple_operand_p.
>
> If we reject comparisons and logical not here, we won't have any
> branching optimization anymore, as this the patch moves into
> fold_truthandor.
>
> The result with rejecting in simple_operand_p compares and logic-not
> provides for the following example:

But you change what simple_operand_p accepts and thus change what
fold_truthop accepts as operands to its simplifications.

Richard.

> extern int doo (void);
> extern int doo2 (void);
>
> int foo (int a, int b, int c, int d, int e, int f)
> {
>  if (a && b && c && d && e && f)
>    return doo ();
>  return doo2 ();
> }
>
> we get the following gimple dump (-fdump-tree-gimple):
>
> foo (int a, int b, int c, int d, int e, int f)
> {
>  int D.2752;
>
>  if (a != 0) goto <D.2740>; else goto <D.2741>;
>  <D.2740>:
>  if (b != 0) goto <D.2742>; else goto <D.2743>;
>  <D.2742>:
>  if (c != 0) goto <D.2744>; else goto <D.2745>;
>  <D.2744>:
>  if (d != 0) goto <D.2746>; else goto <D.2747>;
>  <D.2746>:
>  if (e != 0) goto <D.2748>; else goto <D.2749>;
>  <D.2748>:
>  if (f != 0) goto <D.2750>; else goto <D.2751>;
>  <D.2750>:
>  D.2752 = doo ();
>  return D.2752;
>  <D.2751>:
>  <D.2749>:
>  <D.2747>:
>  <D.2745>:
>  <D.2743>:
>  <D.2741>:
>  D.2752 = doo2 ();
>  return D.2752;
> }
>
> So this result is caused by the fact that a logical-and/or is always a
> comparison.  As we are rejecting comparisons/logical-not,  we end up
> with a sequence of TRUTH_(AND|OR)_IFs.  So the hole loop in
> fold_truth_andor for trying to pack simple and side-effect-less
> operands in tupels of two is useless.
>
> For the new patch (attached with proper ! fix for compares) we get for
> the same sample gimple output:
>
> foo (int a, int b, int c, int d, int e, int f)
> {
>  _Bool D.2740;
>  _Bool D.2741;
>  _Bool D.2742;
>  _Bool D.2745;
>  _Bool D.2746;
>  _Bool D.2747;
>  _Bool D.2750;
>  _Bool D.2751;
>  _Bool D.2752;
>  int D.2755;
>
>  D.2740 = a != 0;
>  D.2741 = b != 0;
>  D.2742 = D.2740 & D.2741;
>  if (D.2742 != 0) goto <D.2743>; else goto <D.2744>;
>  <D.2743>:
>  D.2745 = c != 0;
>  D.2746 = d != 0;
>  D.2747 = D.2745 & D.2746;
>  if (D.2747 != 0) goto <D.2748>; else goto <D.2749>;
>  <D.2748>:
>  D.2750 = e != 0;
>  D.2751 = f != 0;
>  D.2752 = D.2750 & D.2751;
>  if (D.2752 != 0) goto <D.2753>; else goto <D.2754>;
>  <D.2753>:
>  D.2755 = doo ();
>  return D.2755;
>  <D.2754>:
>  <D.2749>:
>  <D.2744>:
>  D.2755 = doo2 ();
>  return D.2755;
> }
>
> which is the proper output for high branching cost, as it tries to
> avoid branches and not to tend them.
>
> --
> Kai
>
> Index: gcc/gcc/fold-const.c
> ===================================================================
> --- gcc.orig/gcc/fold-const.c
> +++ gcc/gcc/fold-const.c
> @@ -111,14 +111,13 @@ static tree decode_field_reference (loca
>                                    tree *, tree *);
>  static int all_ones_mask_p (const_tree, int);
>  static tree sign_bit_p (tree, const_tree);
> -static int simple_operand_p (const_tree);
> +static int simple_operand_p (tree);
>  static tree range_binop (enum tree_code, tree, tree, int, tree, int);
>  static tree range_predecessor (tree);
>  static tree range_successor (tree);
>  static tree fold_range_test (location_t, enum tree_code, tree, tree, tree);
>  static tree fold_cond_expr_with_comparison (location_t, tree, tree,
> tree, tree);
>  static tree unextend (tree, int, int, tree);
> -static tree fold_truthop (location_t, enum tree_code, tree, tree, tree);
>  static tree optimize_minmax_comparison (location_t, enum tree_code,
>                                        tree, tree, tree);
>  static tree extract_muldiv (tree, tree, enum tree_code, tree, bool *);
> @@ -3500,7 +3499,7 @@ optimize_bit_field_compare (location_t l
>   return lhs;
>  }
>
> -/* Subroutine for fold_truthop: decode a field reference.
> +/* Subroutine for fold_truth_andor_1: decode a field reference.
>
>    If EXP is a comparison reference, we return the innermost reference.
>
> @@ -3668,17 +3667,43 @@ sign_bit_p (tree exp, const_tree val)
>   return NULL_TREE;
>  }
>
> -/* Subroutine for fold_truthop: determine if an operand is simple enough
> +/* Subroutine for fold_truth_andor_1: determine if an operand is simple enough
>    to be evaluated unconditionally.  */
>
>  static int
> -simple_operand_p (const_tree exp)
> +simple_operand_p (tree exp)
>  {
> +  enum tree_code code;
>   /* Strip any conversions that don't change the machine mode.  */
>   STRIP_NOPS (exp);
>
> +  code = TREE_CODE (exp);
> +
> +  /* Handle some trivials   */
> +  if (TREE_CODE_CLASS (code) == tcc_comparison)
> +    return (!tree_could_trap_p (exp)
> +           && simple_operand_p (TREE_OPERAND (exp, 0))
> +           && simple_operand_p (TREE_OPERAND (exp, 1)));
> +
> +  if (FLOAT_TYPE_P (TREE_TYPE (exp))
> +      && tree_could_trap_p (exp))
> +    return false;
> +
> +  switch (code)
> +    {
> +    case SSA_NAME:
> +      return true;
> +    case TRUTH_NOT_EXPR:
> +      return simple_operand_p (TREE_OPERAND (exp, 0));
> +    case BIT_NOT_EXPR:
> +      if (TREE_CODE (TREE_TYPE (exp)) != BOOLEAN_TYPE)
> +        return false;
> +      return simple_operand_p (TREE_OPERAND (exp, 0));
> +    default:
> +      break;
> +    }
> +
>   return (CONSTANT_CLASS_P (exp)
> -         || TREE_CODE (exp) == SSA_NAME
>          || (DECL_P (exp)
>              && ! TREE_ADDRESSABLE (exp)
>              && ! TREE_THIS_VOLATILE (exp)
> @@ -4888,7 +4913,7 @@ fold_range_test (location_t loc, enum tr
>   return 0;
>  }
>
> -/* Subroutine for fold_truthop: C is an INTEGER_CST interpreted as a P
> +/* Subroutine for fold_truth_andor_1: C is an INTEGER_CST interpreted as a P
>    bit value.  Arrange things so the extra bits will be set to zero if and
>    only if C is signed-extended to its full width.  If MASK is nonzero,
>    it is an INTEGER_CST that should be AND'ed with the extra bits.  */
> @@ -5025,8 +5050,8 @@ merge_truthop_with_opposite_arm (locatio
>    We return the simplified tree or 0 if no optimization is possible.  */
>
>  static tree
> -fold_truthop (location_t loc, enum tree_code code, tree truth_type,
> -             tree lhs, tree rhs)
> +fold_truth_andor_1 (location_t loc, enum tree_code code, tree truth_type,
> +                   tree lhs, tree rhs)
>  {
>   /* If this is the "or" of two comparisons, we can do something if
>      the comparisons are NE_EXPR.  If this is the "and", we can do something
> @@ -5054,8 +5079,6 @@ fold_truthop (location_t loc, enum tree_
>   tree lntype, rntype, result;
>   HOST_WIDE_INT first_bit, end_bit;
>   int volatilep;
> -  tree orig_lhs = lhs, orig_rhs = rhs;
> -  enum tree_code orig_code = code;
>
>   /* Start by getting the comparison codes.  Fail if anything is volatile.
>      If one operand is a BIT_AND_EXPR with the constant one, treat it as if
> @@ -5119,8 +5142,7 @@ fold_truthop (location_t loc, enum tree_
>   /* If the RHS can be evaluated unconditionally and its operands are
>      simple, it wins to evaluate the RHS unconditionally on machines
>      with expensive branches.  In this case, this isn't a comparison
> -     that can be merged.  Avoid doing this if the RHS is a floating-point
> -     comparison since those can trap.  */
> +     that can be merged.  */
>
>   if (BRANCH_COST (optimize_function_for_speed_p (cfun),
>                   false) >= 2
> @@ -5149,13 +5171,6 @@ fold_truthop (location_t loc, enum tree_
>                           build2 (BIT_IOR_EXPR, TREE_TYPE (ll_arg),
>                                   ll_arg, rl_arg),
>                           build_int_cst (TREE_TYPE (ll_arg), 0));
> -
> -      if (LOGICAL_OP_NON_SHORT_CIRCUIT)
> -       {
> -         if (code != orig_code || lhs != orig_lhs || rhs != orig_rhs)
> -           return build2_loc (loc, code, truth_type, lhs, rhs);
> -         return NULL_TREE;
> -       }
>     }
>
>   /* See if the comparisons can be merged.  Then get all the parameters for
> @@ -8380,13 +8395,46 @@ fold_truth_andor (location_t loc, enum t
>      lhs is another similar operation, try to merge its rhs with our
>      rhs.  Then try to merge our lhs and rhs.  */
>   if (TREE_CODE (arg0) == code
> -      && 0 != (tem = fold_truthop (loc, code, type,
> -                                  TREE_OPERAND (arg0, 1), arg1)))
> +      && 0 != (tem = fold_truth_andor_1 (loc, code, type,
> +                                        TREE_OPERAND (arg0, 1), arg1)))
>     return fold_build2_loc (loc, code, type, TREE_OPERAND (arg0, 0), tem);
>
> -  if ((tem = fold_truthop (loc, code, type, arg0, arg1)) != 0)
> +  if ((tem = fold_truth_andor_1 (loc, code, type, arg0, arg1)) != 0)
>     return tem;
>
> +  if ((code == TRUTH_ANDIF_EXPR || code == TRUTH_ORIF_EXPR)
> +      && (BRANCH_COST (optimize_function_for_speed_p (cfun),
> +                      false) >= 2)
> +      && !TREE_SIDE_EFFECTS (arg1)
> +      && LOGICAL_OP_NON_SHORT_CIRCUIT
> +      && simple_operand_p (arg1))
> +    {
> +      enum tree_code ncode = (code == TRUTH_ANDIF_EXPR ? TRUTH_AND_EXPR
> +                                                      : TRUTH_OR_EXPR);
> +
> +      /* We don't want to pack more then two leafs to an non-IF
> +         If tree-code of left-hand operand isn't an AND/OR-IF code and not
> +         equal to CODE, then we don't want to add right-hand operand.
> +         If the inner right-hand side of left-hand operand has side-effects,
> +         or isn't simple, then we can't add to it, as otherwise we might
> +         destroy if-sequence.  */
> +      if (TREE_CODE (arg0) == code
> +         /* Needed for sequence points to handle trappings, and
> +            side-effects.  */
> +         && !TREE_SIDE_EFFECTS (TREE_OPERAND (arg0, 1))
> +         && simple_operand_p (TREE_OPERAND (arg0, 1)))
> +       {
> +         tem = fold_build2_loc (loc, ncode, type, TREE_OPERAND (arg0, 1),
> +                               arg1);
> +         return fold_build2_loc (loc, code, type, TREE_OPERAND (arg0, 0),
> +                                tem);
> +       }
> +     /* Needed for sequence points to handle trappings, and side-effects.  */
> +     else if (!TREE_SIDE_EFFECTS (arg0)
> +             && simple_operand_p (arg0))
> +       return fold_build2_loc (loc, ncode, type, arg0, arg1);
> +    }
> +
>   return NULL_TREE;
>  }
>
Kai Tietz - Oct. 10, 2011, 3:07 p.m.
2011/10/10 Richard Guenther <richard.guenther@gmail.com>:
> On Mon, Oct 10, 2011 at 4:06 PM, Kai Tietz <ktietz70@googlemail.com> wrote:
>> 2011/10/10 Richard Guenther <richard.guenther@gmail.com>:
>>> On Mon, Oct 10, 2011 at 2:29 PM, Kai Tietz <ktietz70@googlemail.com> wrote:
>>>> Recent patch had a thinko on rhs of inner lhs check for TRUTH-IF.  It
>>>> has to be checked that the LHS code is same as outer CODE, as
>>>> otherwise we wouldn't apply different TRUTH-IF only on inner RHS of
>>>> LHS, which is of course wrong.
>>>>
>>>> Index: gcc/gcc/fold-const.c
>>>> ===================================================================
>>>> --- gcc.orig/gcc/fold-const.c
>>>> +++ gcc/gcc/fold-const.c
>>>> @@ -111,14 +111,13 @@ static tree decode_field_reference (loca
>>>>                                    tree *, tree *);
>>>>  static int all_ones_mask_p (const_tree, int);
>>>>  static tree sign_bit_p (tree, const_tree);
>>>> -static int simple_operand_p (const_tree);
>>>> +static int simple_operand_p (tree);
>>>>  static tree range_binop (enum tree_code, tree, tree, int, tree, int);
>>>>  static tree range_predecessor (tree);
>>>>  static tree range_successor (tree);
>>>>  static tree fold_range_test (location_t, enum tree_code, tree, tree, tree);
>>>>  static tree fold_cond_expr_with_comparison (location_t, tree, tree,
>>>> tree, tree);
>>>>  static tree unextend (tree, int, int, tree);
>>>> -static tree fold_truthop (location_t, enum tree_code, tree, tree, tree);
>>>>  static tree optimize_minmax_comparison (location_t, enum tree_code,
>>>>                                        tree, tree, tree);
>>>>  static tree extract_muldiv (tree, tree, enum tree_code, tree, bool *);
>>>> @@ -3500,7 +3499,7 @@ optimize_bit_field_compare (location_t l
>>>>   return lhs;
>>>>  }
>>>>
>>>> -/* Subroutine for fold_truthop: decode a field reference.
>>>> +/* Subroutine for fold_truth_andor_1: decode a field reference.
>>>>
>>>>    If EXP is a comparison reference, we return the innermost reference.
>>>>
>>>> @@ -3668,17 +3667,43 @@ sign_bit_p (tree exp, const_tree val)
>>>>   return NULL_TREE;
>>>>  }
>>>>
>>>> -/* Subroutine for fold_truthop: determine if an operand is simple enough
>>>> +/* Subroutine for fold_truth_andor_1: determine if an operand is simple enough
>>>>    to be evaluated unconditionally.  */
>>>>
>>>>  static int
>>>> -simple_operand_p (const_tree exp)
>>>> +simple_operand_p (tree exp)
>>>>  {
>>>> +  enum tree_code code;
>>>>   /* Strip any conversions that don't change the machine mode.  */
>>>>   STRIP_NOPS (exp);
>>>>
>>>> +  code = TREE_CODE (exp);
>>>> +
>>>> +  /* Handle some trivials   */
>>>> +  if (TREE_CODE_CLASS (code) == tcc_comparison)
>>>> +    return (tree_could_trap_p (exp)
>>>> +           && simple_operand_p (TREE_OPERAND (exp, 0))
>>>> +           && simple_operand_p (TREE_OPERAND (exp, 1)));
>>>
>>> And that's still wrong.
>>>
>>> Stopped reading here.
>>>
>>> Richard.
>>
>> Oh, there is a not missing.  I didn't spot that, sorry.
>>
>> To the point why we need to handle comparisons within simple_operand_p.
>>
>> If we reject comparisons and logical not here, we won't have any
>> branching optimization anymore, as this the patch moves into
>> fold_truthandor.
>>
>> The result with rejecting in simple_operand_p compares and logic-not
>> provides for the following example:
>
> But you change what simple_operand_p accepts and thus change what
> fold_truthop accepts as operands to its simplifications.
>
> Richard.

Well, not really.  I assume you mean fold_truth_andor_1 (aka fold_truthop).

It checks for
...
  if (TREE_CODE_CLASS (lcode) != tcc_comparison
      || TREE_CODE_CLASS (rcode) != tcc_comparison)
    return 0;
...
before checking for simple_operand_p.  So there is actual no change.
It might be of some interest here to add in a different patch support
for logic-not, but well, this is would be material for a different
patch.
So, it won't operate on anything else then comparisons as before.

Kai
Richard Guenther - Oct. 10, 2011, 3:35 p.m.
On Mon, Oct 10, 2011 at 5:07 PM, Kai Tietz <ktietz70@googlemail.com> wrote:
> 2011/10/10 Richard Guenther <richard.guenther@gmail.com>:
>> On Mon, Oct 10, 2011 at 4:06 PM, Kai Tietz <ktietz70@googlemail.com> wrote:
>>> 2011/10/10 Richard Guenther <richard.guenther@gmail.com>:
>>>> On Mon, Oct 10, 2011 at 2:29 PM, Kai Tietz <ktietz70@googlemail.com> wrote:
>>>>> Recent patch had a thinko on rhs of inner lhs check for TRUTH-IF.  It
>>>>> has to be checked that the LHS code is same as outer CODE, as
>>>>> otherwise we wouldn't apply different TRUTH-IF only on inner RHS of
>>>>> LHS, which is of course wrong.
>>>>>
>>>>> Index: gcc/gcc/fold-const.c
>>>>> ===================================================================
>>>>> --- gcc.orig/gcc/fold-const.c
>>>>> +++ gcc/gcc/fold-const.c
>>>>> @@ -111,14 +111,13 @@ static tree decode_field_reference (loca
>>>>>                                    tree *, tree *);
>>>>>  static int all_ones_mask_p (const_tree, int);
>>>>>  static tree sign_bit_p (tree, const_tree);
>>>>> -static int simple_operand_p (const_tree);
>>>>> +static int simple_operand_p (tree);
>>>>>  static tree range_binop (enum tree_code, tree, tree, int, tree, int);
>>>>>  static tree range_predecessor (tree);
>>>>>  static tree range_successor (tree);
>>>>>  static tree fold_range_test (location_t, enum tree_code, tree, tree, tree);
>>>>>  static tree fold_cond_expr_with_comparison (location_t, tree, tree,
>>>>> tree, tree);
>>>>>  static tree unextend (tree, int, int, tree);
>>>>> -static tree fold_truthop (location_t, enum tree_code, tree, tree, tree);
>>>>>  static tree optimize_minmax_comparison (location_t, enum tree_code,
>>>>>                                        tree, tree, tree);
>>>>>  static tree extract_muldiv (tree, tree, enum tree_code, tree, bool *);
>>>>> @@ -3500,7 +3499,7 @@ optimize_bit_field_compare (location_t l
>>>>>   return lhs;
>>>>>  }
>>>>>
>>>>> -/* Subroutine for fold_truthop: decode a field reference.
>>>>> +/* Subroutine for fold_truth_andor_1: decode a field reference.
>>>>>
>>>>>    If EXP is a comparison reference, we return the innermost reference.
>>>>>
>>>>> @@ -3668,17 +3667,43 @@ sign_bit_p (tree exp, const_tree val)
>>>>>   return NULL_TREE;
>>>>>  }
>>>>>
>>>>> -/* Subroutine for fold_truthop: determine if an operand is simple enough
>>>>> +/* Subroutine for fold_truth_andor_1: determine if an operand is simple enough
>>>>>    to be evaluated unconditionally.  */
>>>>>
>>>>>  static int
>>>>> -simple_operand_p (const_tree exp)
>>>>> +simple_operand_p (tree exp)
>>>>>  {
>>>>> +  enum tree_code code;
>>>>>   /* Strip any conversions that don't change the machine mode.  */
>>>>>   STRIP_NOPS (exp);
>>>>>
>>>>> +  code = TREE_CODE (exp);
>>>>> +
>>>>> +  /* Handle some trivials   */
>>>>> +  if (TREE_CODE_CLASS (code) == tcc_comparison)
>>>>> +    return (tree_could_trap_p (exp)
>>>>> +           && simple_operand_p (TREE_OPERAND (exp, 0))
>>>>> +           && simple_operand_p (TREE_OPERAND (exp, 1)));
>>>>
>>>> And that's still wrong.
>>>>
>>>> Stopped reading here.
>>>>
>>>> Richard.
>>>
>>> Oh, there is a not missing.  I didn't spot that, sorry.
>>>
>>> To the point why we need to handle comparisons within simple_operand_p.
>>>
>>> If we reject comparisons and logical not here, we won't have any
>>> branching optimization anymore, as this the patch moves into
>>> fold_truthandor.
>>>
>>> The result with rejecting in simple_operand_p compares and logic-not
>>> provides for the following example:
>>
>> But you change what simple_operand_p accepts and thus change what
>> fold_truthop accepts as operands to its simplifications.
>>
>> Richard.
>
> Well, not really.  I assume you mean fold_truth_andor_1 (aka fold_truthop).
>
> It checks for
> ...
>  if (TREE_CODE_CLASS (lcode) != tcc_comparison
>      || TREE_CODE_CLASS (rcode) != tcc_comparison)
>    return 0;
> ...
> before checking for simple_operand_p.  So there is actual no change.
> It might be of some interest here to add in a different patch support
> for logic-not, but well, this is would be material for a different
> patch.
> So, it won't operate on anything else then comparisons as before.

Sure, because simple_operand_p is checked on the comparison
operands, not the comparison itself.

Richard.

> Kai
>

Patch

Index: gcc/gcc/fold-const.c
===================================================================
--- gcc.orig/gcc/fold-const.c
+++ gcc/gcc/fold-const.c
@@ -111,14 +111,13 @@  static tree decode_field_reference (loca
 				    tree *, tree *);
 static int all_ones_mask_p (const_tree, int);
 static tree sign_bit_p (tree, const_tree);
-static int simple_operand_p (const_tree);
+static int simple_operand_p (tree);
 static tree range_binop (enum tree_code, tree, tree, int, tree, int);
 static tree range_predecessor (tree);
 static tree range_successor (tree);
 static tree fold_range_test (location_t, enum tree_code, tree, tree, tree);
 static tree fold_cond_expr_with_comparison (location_t, tree, tree,
tree, tree);
 static tree unextend (tree, int, int, tree);
-static tree fold_truthop (location_t, enum tree_code, tree, tree, tree);
 static tree optimize_minmax_comparison (location_t, enum tree_code,
 					tree, tree, tree);