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

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Submitter Kai Tietz
Date Oct. 7, 2011, 9:36 p.m.
Message ID <CAEwic4bRXG6gXi+MWxAN8W_4bECOmXwOUngG6FZ+F=7j-kLb=g@mail.gmail.com>
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Permalink /patch/118374/
State New
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Kai Tietz - Oct. 7, 2011, 9:36 p.m.
Hello,

this is the updated version with the suggestion

2011/10/7 Richard Guenther <richard.guenther@gmail.com>:
> On Thu, Oct 6, 2011 at 4:25 PM, Kai Tietz <ktietz@redhat.com> wrote:
>> +      && ((TREE_CODE_CLASS (TREE_CODE (arg1)) != tcc_comparison
>> +           && TREE_CODE (arg1) != TRUTH_NOT_EXPR
>> +           && simple_operand_p (arg1))
>
> As I said previously simple_operand_p already rejects covers
> comparisons and TRUTH_NOT_EXPR.  Also arg1 had better
> TREE_SIDE_EFFECTS set if the comparison might trap, as
> it might just be hidden in something more complicated - so
> the simple check isn't enough anyway (and if simple_operand_p
> would cover it, the check would be better placed there).

I reworked simple_operand_p so that it does this special-casing and additionally
also checks for trapping.

>> +      if (TREE_CODE (arg0) == code
>> +          && !TREE_SIDE_EFFECTS (TREE_OPERAND (arg0, 1))
>> +          && simple_operand_p (TREE_OPERAND (arg0, 1)))
>> +       {
>> +         tem = build2_loc (loc,
>> +                           (code == TRUTH_ANDIF_EXPR ? TRUTH_AND_EXPR
>> +                                                     : TRUTH_OR_EXPR),
>> +                           type, TREE_OPERAND (arg0, 1), arg1);
>> +         return build2_loc (loc, code, type, TREE_OPERAND (arg0, 0),
>> +                            tem);
>
> All trees should be folded, don't use plain build without a good reason.

Ok, done

>> +       }
>> +      /* Convert X TRUTH-ANDORIF Y to X TRUTH-ANDOR Y, if X and Y
>> +        are simple operands and have no side-effects.  */
>> +      if (simple_operand_p (arg0)
>> +          && !TREE_SIDE_EFFECTS (arg0))
>
> Again, the checks you do for arg0 do not match those for arg1.  OTOH
> it doesn't matter whether arg0 is simple or not or has side-effects or
> not for this transformation, so why check it at all?

It is required.  For left-hand operand, if it isn't a logical
and/or/xor, we need to check for side-effects (and for trapping).  I
see that calling of simple_operand_p is wrong here, as it rejects too
much.  Nevertheless the check for side-effects is necessary for having
valid sequence-points.  Without that checking a simple test

int getter (void);

int foo (void)
{
  int c, r = 0;
  while ((c = getter ()) != '"' && c >= 0)
    r +=c;
  return r;
}

would give a warning about sequence-points.  As left-hand operand has
side-effects, but right-hand not.  If we would combine it as AND, the
operands are exchange-able.  So right-hand operand needs to be another
ANDIF expression instead.
Same apply on trapping.

> In fold_truthop we still have the same (albeit more restricted transform),
> but guarded with
>
>  if (BRANCH_COST (optimize_function_for_speed_p (cfun),
>                   false) >= 2
>
> too.  Why not here?  Please delete redundant code in fold_truthop.
Well, in general this is the default definition of
LOGICAL_OP_NON_SHORT_CIRCUIT, so I missed that.  As for some targets
the macro LOGICAL_OP_NON_SHORT_CIRCUIT might be defined differently,
it might make sense to check for BRANCH_COST again.

> It's also odd that this is only called from fold_truth_andor but has
> a more generic name, so maybe rename it to fold_truth_andor_1 on the way.

I renamed it.

> Richard.

ChangeLog

2011-10-07  Kai Tietz  <ktietz@redhat.com>

	* fold-const.c (simple_operand_p): Make argument non-const
	and add floating-point trapping check, and special cases for
	comparisons, and logical-not's.
	(fold_truthop): Rename to
	(fold_truth_andor_1): function name.
	Additionally remove here TRUTH-AND|OR_EXPR generation.
	(fold_truth_andor): Handle branching at one place.

Bootstrapped and regression-tested for all languages plus Ada and
Obj-C++ on x86_64-pc-linux-gnu.
Ok for apply?

Regards,
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 +8395,52 @@ 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 non-IF branches
+         together.  Therefore we need to check, if rhs isn't
+         already an TRUTH_(XOR|OR|AND)[IF]_EXPR.  */
+      if (TREE_CODE (arg0) == code
+      	  && TREE_CODE (TREE_OPERAND (arg0, 1)) != TRUTH_AND_EXPR
+      	  && TREE_CODE (TREE_OPERAND (arg0, 1)) != TRUTH_OR_EXPR
+      	  && TREE_CODE (TREE_OPERAND (arg0, 1)) != TRUTH_XOR_EXPR
+      	  && TREE_CODE (TREE_OPERAND (arg0, 1)) != TRUTH_ANDIF_EXPR
+      	  && TREE_CODE (TREE_OPERAND (arg0, 1)) != TRUTH_ORIF_EXPR
+      	  /* Needed for sequence points and trappings, or side-effects.  */
+      	  && !TREE_SIDE_EFFECTS (TREE_OPERAND (arg0, 1))
+      	  && !tree_could_trap_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);
+       }
+     else if (TREE_CODE (arg0) != TRUTH_AND_EXPR
+	      && TREE_CODE (arg0) != TRUTH_OR_EXPR
+	      && TREE_CODE (arg0) != TRUTH_ANDIF_EXPR
+	      && TREE_CODE (arg0) != TRUTH_ORIF_EXPR
+	      && TREE_CODE (arg0) != TRUTH_XOR_EXPR
+	      /* Needed for sequence points and trappings, or side-effects.  */
+	      && !TREE_SIDE_EFFECTS (arg0)
+	      && !tree_could_trap_p (arg0))
+       return fold_build2_loc (loc, ncode, type, arg0, arg1);
+    }
+
   return NULL_TREE;
 }
Kai Tietz - Oct. 10, 2011, 10:35 a.m.
2011/10/7 Kai Tietz <ktietz70@googlemail.com>:
> Hello,
>
> this is the updated version with the suggestion
>
> 2011/10/7 Richard Guenther <richard.guenther@gmail.com>:
>> On Thu, Oct 6, 2011 at 4:25 PM, Kai Tietz <ktietz@redhat.com> wrote:
>>> +      && ((TREE_CODE_CLASS (TREE_CODE (arg1)) != tcc_comparison
>>> +           && TREE_CODE (arg1) != TRUTH_NOT_EXPR
>>> +           && simple_operand_p (arg1))
>>
>> As I said previously simple_operand_p already rejects covers
>> comparisons and TRUTH_NOT_EXPR.  Also arg1 had better
>> TREE_SIDE_EFFECTS set if the comparison might trap, as
>> it might just be hidden in something more complicated - so
>> the simple check isn't enough anyway (and if simple_operand_p
>> would cover it, the check would be better placed there).
>
> I reworked simple_operand_p so that it does this special-casing and additionally
> also checks for trapping.
>
>>> +      if (TREE_CODE (arg0) == code
>>> +          && !TREE_SIDE_EFFECTS (TREE_OPERAND (arg0, 1))
>>> +          && simple_operand_p (TREE_OPERAND (arg0, 1)))
>>> +       {
>>> +         tem = build2_loc (loc,
>>> +                           (code == TRUTH_ANDIF_EXPR ? TRUTH_AND_EXPR
>>> +                                                     : TRUTH_OR_EXPR),
>>> +                           type, TREE_OPERAND (arg0, 1), arg1);
>>> +         return build2_loc (loc, code, type, TREE_OPERAND (arg0, 0),
>>> +                            tem);
>>
>> All trees should be folded, don't use plain build without a good reason.
>
> Ok, done
>
>>> +       }
>>> +      /* Convert X TRUTH-ANDORIF Y to X TRUTH-ANDOR Y, if X and Y
>>> +        are simple operands and have no side-effects.  */
>>> +      if (simple_operand_p (arg0)
>>> +          && !TREE_SIDE_EFFECTS (arg0))
>>
>> Again, the checks you do for arg0 do not match those for arg1.  OTOH
>> it doesn't matter whether arg0 is simple or not or has side-effects or
>> not for this transformation, so why check it at all?
>
> It is required.  For left-hand operand, if it isn't a logical
> and/or/xor, we need to check for side-effects (and for trapping).  I
> see that calling of simple_operand_p is wrong here, as it rejects too
> much.  Nevertheless the check for side-effects is necessary for having
> valid sequence-points.  Without that checking a simple test

So said, it is even required to use for right-hand and left-hand side
of arguments, if one of them have side-effects or isn't simple.  Means
the check in my patch should use for

> +     else if (TREE_CODE (arg0) != TRUTH_AND_EXPR
> +             && TREE_CODE (arg0) != TRUTH_OR_EXPR
> +             && TREE_CODE (arg0) != TRUTH_ANDIF_EXPR
> +             && TREE_CODE (arg0) != TRUTH_ORIF_EXPR
> +             && TREE_CODE (arg0) != TRUTH_XOR_EXPR
> +             /* Needed for sequence points and trappings, or side-effects.  */
> +             && !TREE_SIDE_EFFECTS (arg0)
> +             && !tree_could_trap_p (arg0))
> +       return fold_build2_loc (loc, ncode, type, arg0, arg1);

instead if (!TREE_SIDE_EFFECTS (arg0) && simple_operand_p (arg0)) ....
instead.

The cause for this are the consitancies of sequences in tree.  I
noticed that by tests in gcc.dg/tree-ssa about builitin_expect.

for example we have

extern int foo (void); /* foo modifies gbl1 */
int gbl1 = 0;

int foo (int ns1)
{
  if (ns1 && foo () && gbl1)
    return 1;
  return 0;
}

so chain of trees has to look like this:
(ANDIF (ns1 (ANDIF foo () gbl1))

but if we don't check here for side-effects for left-hand chaining
operand, then we end up with
(AND ns1 (ANDIF foo () gbl1))

As AND and has associative property, tree says that right-hand and
left-hand are exchangable, which is obviously wrong.

Cheers,
Kai
Richard Guenther - Oct. 10, 2011, 10:40 a.m.
On Mon, Oct 10, 2011 at 12:35 PM, Kai Tietz <ktietz70@googlemail.com> wrote:
> 2011/10/7 Kai Tietz <ktietz70@googlemail.com>:
>> Hello,
>>
>> this is the updated version with the suggestion
>>
>> 2011/10/7 Richard Guenther <richard.guenther@gmail.com>:
>>> On Thu, Oct 6, 2011 at 4:25 PM, Kai Tietz <ktietz@redhat.com> wrote:
>>>> +      && ((TREE_CODE_CLASS (TREE_CODE (arg1)) != tcc_comparison
>>>> +           && TREE_CODE (arg1) != TRUTH_NOT_EXPR
>>>> +           && simple_operand_p (arg1))
>>>
>>> As I said previously simple_operand_p already rejects covers
>>> comparisons and TRUTH_NOT_EXPR.  Also arg1 had better
>>> TREE_SIDE_EFFECTS set if the comparison might trap, as
>>> it might just be hidden in something more complicated - so
>>> the simple check isn't enough anyway (and if simple_operand_p
>>> would cover it, the check would be better placed there).
>>
>> I reworked simple_operand_p so that it does this special-casing and additionally
>> also checks for trapping.
>>
>>>> +      if (TREE_CODE (arg0) == code
>>>> +          && !TREE_SIDE_EFFECTS (TREE_OPERAND (arg0, 1))
>>>> +          && simple_operand_p (TREE_OPERAND (arg0, 1)))
>>>> +       {
>>>> +         tem = build2_loc (loc,
>>>> +                           (code == TRUTH_ANDIF_EXPR ? TRUTH_AND_EXPR
>>>> +                                                     : TRUTH_OR_EXPR),
>>>> +                           type, TREE_OPERAND (arg0, 1), arg1);
>>>> +         return build2_loc (loc, code, type, TREE_OPERAND (arg0, 0),
>>>> +                            tem);
>>>
>>> All trees should be folded, don't use plain build without a good reason.
>>
>> Ok, done
>>
>>>> +       }
>>>> +      /* Convert X TRUTH-ANDORIF Y to X TRUTH-ANDOR Y, if X and Y
>>>> +        are simple operands and have no side-effects.  */
>>>> +      if (simple_operand_p (arg0)
>>>> +          && !TREE_SIDE_EFFECTS (arg0))
>>>
>>> Again, the checks you do for arg0 do not match those for arg1.  OTOH
>>> it doesn't matter whether arg0 is simple or not or has side-effects or
>>> not for this transformation, so why check it at all?
>>
>> It is required.  For left-hand operand, if it isn't a logical
>> and/or/xor, we need to check for side-effects (and for trapping).  I
>> see that calling of simple_operand_p is wrong here, as it rejects too
>> much.  Nevertheless the check for side-effects is necessary for having
>> valid sequence-points.  Without that checking a simple test
>
> So said, it is even required to use for right-hand and left-hand side
> of arguments, if one of them have side-effects or isn't simple.  Means
> the check in my patch should use for
>
>> +     else if (TREE_CODE (arg0) != TRUTH_AND_EXPR
>> +             && TREE_CODE (arg0) != TRUTH_OR_EXPR
>> +             && TREE_CODE (arg0) != TRUTH_ANDIF_EXPR
>> +             && TREE_CODE (arg0) != TRUTH_ORIF_EXPR
>> +             && TREE_CODE (arg0) != TRUTH_XOR_EXPR
>> +             /* Needed for sequence points and trappings, or side-effects.  */
>> +             && !TREE_SIDE_EFFECTS (arg0)
>> +             && !tree_could_trap_p (arg0))
>> +       return fold_build2_loc (loc, ncode, type, arg0, arg1);
>
> instead if (!TREE_SIDE_EFFECTS (arg0) && simple_operand_p (arg0)) ....
> instead.
>
> The cause for this are the consitancies of sequences in tree.  I
> noticed that by tests in gcc.dg/tree-ssa about builitin_expect.
>
> for example we have
>
> extern int foo (void); /* foo modifies gbl1 */
> int gbl1 = 0;
>
> int foo (int ns1)
> {
>  if (ns1 && foo () && gbl1)
>    return 1;
>  return 0;
> }
>
> so chain of trees has to look like this:
> (ANDIF (ns1 (ANDIF foo () gbl1))
>
> but if we don't check here for side-effects for left-hand chaining
> operand, then we end up with
> (AND ns1 (ANDIF foo () gbl1))

No we don't, as the right-hand (ANDIF foo () glbl1) has side-effects.

> As AND and has associative property, tree says that right-hand and
> left-hand are exchangable, which is obviously wrong.

The poitn is that if the right-hand does not have side-effects it doesn't
matter if we execute it before the left-hand (independent on whether
that has side-effects or not).

Richard.

> Cheers,
> Kai
>
Kai Tietz - Oct. 10, 2011, 10:47 a.m.
2011/10/10 Richard Guenther <richard.guenther@gmail.com>:
> On Mon, Oct 10, 2011 at 12:35 PM, Kai Tietz <ktietz70@googlemail.com> wrote:
>> 2011/10/7 Kai Tietz <ktietz70@googlemail.com>:
>>> Hello,
>>>
>>> this is the updated version with the suggestion
>>>
>>> 2011/10/7 Richard Guenther <richard.guenther@gmail.com>:
>>>> On Thu, Oct 6, 2011 at 4:25 PM, Kai Tietz <ktietz@redhat.com> wrote:
>>>>> +      && ((TREE_CODE_CLASS (TREE_CODE (arg1)) != tcc_comparison
>>>>> +           && TREE_CODE (arg1) != TRUTH_NOT_EXPR
>>>>> +           && simple_operand_p (arg1))
>>>>
>>>> As I said previously simple_operand_p already rejects covers
>>>> comparisons and TRUTH_NOT_EXPR.  Also arg1 had better
>>>> TREE_SIDE_EFFECTS set if the comparison might trap, as
>>>> it might just be hidden in something more complicated - so
>>>> the simple check isn't enough anyway (and if simple_operand_p
>>>> would cover it, the check would be better placed there).
>>>
>>> I reworked simple_operand_p so that it does this special-casing and additionally
>>> also checks for trapping.
>>>
>>>>> +      if (TREE_CODE (arg0) == code
>>>>> +          && !TREE_SIDE_EFFECTS (TREE_OPERAND (arg0, 1))
>>>>> +          && simple_operand_p (TREE_OPERAND (arg0, 1)))
>>>>> +       {
>>>>> +         tem = build2_loc (loc,
>>>>> +                           (code == TRUTH_ANDIF_EXPR ? TRUTH_AND_EXPR
>>>>> +                                                     : TRUTH_OR_EXPR),
>>>>> +                           type, TREE_OPERAND (arg0, 1), arg1);
>>>>> +         return build2_loc (loc, code, type, TREE_OPERAND (arg0, 0),
>>>>> +                            tem);
>>>>
>>>> All trees should be folded, don't use plain build without a good reason.
>>>
>>> Ok, done
>>>
>>>>> +       }
>>>>> +      /* Convert X TRUTH-ANDORIF Y to X TRUTH-ANDOR Y, if X and Y
>>>>> +        are simple operands and have no side-effects.  */
>>>>> +      if (simple_operand_p (arg0)
>>>>> +          && !TREE_SIDE_EFFECTS (arg0))
>>>>
>>>> Again, the checks you do for arg0 do not match those for arg1.  OTOH
>>>> it doesn't matter whether arg0 is simple or not or has side-effects or
>>>> not for this transformation, so why check it at all?
>>>
>>> It is required.  For left-hand operand, if it isn't a logical
>>> and/or/xor, we need to check for side-effects (and for trapping).  I
>>> see that calling of simple_operand_p is wrong here, as it rejects too
>>> much.  Nevertheless the check for side-effects is necessary for having
>>> valid sequence-points.  Without that checking a simple test
>>
>> So said, it is even required to use for right-hand and left-hand side
>> of arguments, if one of them have side-effects or isn't simple.  Means
>> the check in my patch should use for
>>
>>> +     else if (TREE_CODE (arg0) != TRUTH_AND_EXPR
>>> +             && TREE_CODE (arg0) != TRUTH_OR_EXPR
>>> +             && TREE_CODE (arg0) != TRUTH_ANDIF_EXPR
>>> +             && TREE_CODE (arg0) != TRUTH_ORIF_EXPR
>>> +             && TREE_CODE (arg0) != TRUTH_XOR_EXPR
>>> +             /* Needed for sequence points and trappings, or side-effects.  */
>>> +             && !TREE_SIDE_EFFECTS (arg0)
>>> +             && !tree_could_trap_p (arg0))
>>> +       return fold_build2_loc (loc, ncode, type, arg0, arg1);
>>
>> instead if (!TREE_SIDE_EFFECTS (arg0) && simple_operand_p (arg0)) ....
>> instead.
>>
>> The cause for this are the consitancies of sequences in tree.  I
>> noticed that by tests in gcc.dg/tree-ssa about builitin_expect.
>>
>> for example we have
>>
>> extern int foo (void); /* foo modifies gbl1 */
>> int gbl1 = 0;
>>
>> int foo (int ns1)
>> {
>>  if (ns1 && foo () && gbl1)
>>    return 1;
>>  return 0;
>> }
>>
>> so chain of trees has to look like this:
>> (ANDIF (ns1 (ANDIF foo () gbl1))
>>
>> but if we don't check here for side-effects for left-hand chaining
>> operand, then we end up with
>> (AND ns1 (ANDIF foo () gbl1))
>
> No we don't, as the right-hand (ANDIF foo () glbl1) has side-effects.
>
>> As AND and has associative property, tree says that right-hand and
>> left-hand are exchangable, which is obviously wrong.
>
> The poitn is that if the right-hand does not have side-effects it doesn't
> matter if we execute it before the left-hand (independent on whether
> that has side-effects or not).
>
> Richard.

thats just true as long as we don't make use of associative law for
AND expressions.
Otherwise we would fail for much simpler cases like
entern int doo ();
int foo ()
{
  int c, r = 0;
  if ((c = foo ()) != 0 && c < 20)
    r = 1;
  return 0;
}

as for this left-hand operand has side-effects, but as it is the first
one, we would chain it as AND.  So we get wrong sequence.

Kai
Kai Tietz - Oct. 10, 2011, 10:58 a.m.
Sample had a typo. Correct sample has of course to return r.

 int foo ()
 {
  int c, r = 0;
  if ((c = foo ()) != 0 && c < 20)
    r = 1;
  return r;
}
Richard Guenther - Oct. 10, 2011, 11:15 a.m.
On Mon, Oct 10, 2011 at 12:47 PM, Kai Tietz <ktietz70@googlemail.com> wrote:
> 2011/10/10 Richard Guenther <richard.guenther@gmail.com>:
>> On Mon, Oct 10, 2011 at 12:35 PM, Kai Tietz <ktietz70@googlemail.com> wrote:
>>> 2011/10/7 Kai Tietz <ktietz70@googlemail.com>:
>>>> Hello,
>>>>
>>>> this is the updated version with the suggestion
>>>>
>>>> 2011/10/7 Richard Guenther <richard.guenther@gmail.com>:
>>>>> On Thu, Oct 6, 2011 at 4:25 PM, Kai Tietz <ktietz@redhat.com> wrote:
>>>>>> +      && ((TREE_CODE_CLASS (TREE_CODE (arg1)) != tcc_comparison
>>>>>> +           && TREE_CODE (arg1) != TRUTH_NOT_EXPR
>>>>>> +           && simple_operand_p (arg1))
>>>>>
>>>>> As I said previously simple_operand_p already rejects covers
>>>>> comparisons and TRUTH_NOT_EXPR.  Also arg1 had better
>>>>> TREE_SIDE_EFFECTS set if the comparison might trap, as
>>>>> it might just be hidden in something more complicated - so
>>>>> the simple check isn't enough anyway (and if simple_operand_p
>>>>> would cover it, the check would be better placed there).
>>>>
>>>> I reworked simple_operand_p so that it does this special-casing and additionally
>>>> also checks for trapping.
>>>>
>>>>>> +      if (TREE_CODE (arg0) == code
>>>>>> +          && !TREE_SIDE_EFFECTS (TREE_OPERAND (arg0, 1))
>>>>>> +          && simple_operand_p (TREE_OPERAND (arg0, 1)))
>>>>>> +       {
>>>>>> +         tem = build2_loc (loc,
>>>>>> +                           (code == TRUTH_ANDIF_EXPR ? TRUTH_AND_EXPR
>>>>>> +                                                     : TRUTH_OR_EXPR),
>>>>>> +                           type, TREE_OPERAND (arg0, 1), arg1);
>>>>>> +         return build2_loc (loc, code, type, TREE_OPERAND (arg0, 0),
>>>>>> +                            tem);
>>>>>
>>>>> All trees should be folded, don't use plain build without a good reason.
>>>>
>>>> Ok, done
>>>>
>>>>>> +       }
>>>>>> +      /* Convert X TRUTH-ANDORIF Y to X TRUTH-ANDOR Y, if X and Y
>>>>>> +        are simple operands and have no side-effects.  */
>>>>>> +      if (simple_operand_p (arg0)
>>>>>> +          && !TREE_SIDE_EFFECTS (arg0))
>>>>>
>>>>> Again, the checks you do for arg0 do not match those for arg1.  OTOH
>>>>> it doesn't matter whether arg0 is simple or not or has side-effects or
>>>>> not for this transformation, so why check it at all?
>>>>
>>>> It is required.  For left-hand operand, if it isn't a logical
>>>> and/or/xor, we need to check for side-effects (and for trapping).  I
>>>> see that calling of simple_operand_p is wrong here, as it rejects too
>>>> much.  Nevertheless the check for side-effects is necessary for having
>>>> valid sequence-points.  Without that checking a simple test
>>>
>>> So said, it is even required to use for right-hand and left-hand side
>>> of arguments, if one of them have side-effects or isn't simple.  Means
>>> the check in my patch should use for
>>>
>>>> +     else if (TREE_CODE (arg0) != TRUTH_AND_EXPR
>>>> +             && TREE_CODE (arg0) != TRUTH_OR_EXPR
>>>> +             && TREE_CODE (arg0) != TRUTH_ANDIF_EXPR
>>>> +             && TREE_CODE (arg0) != TRUTH_ORIF_EXPR
>>>> +             && TREE_CODE (arg0) != TRUTH_XOR_EXPR
>>>> +             /* Needed for sequence points and trappings, or side-effects.  */
>>>> +             && !TREE_SIDE_EFFECTS (arg0)
>>>> +             && !tree_could_trap_p (arg0))
>>>> +       return fold_build2_loc (loc, ncode, type, arg0, arg1);
>>>
>>> instead if (!TREE_SIDE_EFFECTS (arg0) && simple_operand_p (arg0)) ....
>>> instead.
>>>
>>> The cause for this are the consitancies of sequences in tree.  I
>>> noticed that by tests in gcc.dg/tree-ssa about builitin_expect.
>>>
>>> for example we have
>>>
>>> extern int foo (void); /* foo modifies gbl1 */
>>> int gbl1 = 0;
>>>
>>> int foo (int ns1)
>>> {
>>>  if (ns1 && foo () && gbl1)
>>>    return 1;
>>>  return 0;
>>> }
>>>
>>> so chain of trees has to look like this:
>>> (ANDIF (ns1 (ANDIF foo () gbl1))
>>>
>>> but if we don't check here for side-effects for left-hand chaining
>>> operand, then we end up with
>>> (AND ns1 (ANDIF foo () gbl1))
>>
>> No we don't, as the right-hand (ANDIF foo () glbl1) has side-effects.
>>
>>> As AND and has associative property, tree says that right-hand and
>>> left-hand are exchangable, which is obviously wrong.
>>
>> The poitn is that if the right-hand does not have side-effects it doesn't
>> matter if we execute it before the left-hand (independent on whether
>> that has side-effects or not).
>>
>> Richard.
>
> thats just true as long as we don't make use of associative law for
> AND expressions.
> Otherwise we would fail for much simpler cases like
> entern int doo ();
> int foo ()
> {
>  int c, r = 0;
>  if ((c = foo ()) != 0 && c < 20)
>    r = 1;
>  return 0;
> }
>
> as for this left-hand operand has side-effects, but as it is the first
> one, we would chain it as AND.  So we get wrong sequence.

Well, then the predicates checking for simplicity and side-effects
should better match.

Richard.

> Kai
>
Richard Guenther - Oct. 10, 2011, 11:20 a.m.
On Fri, Oct 7, 2011 at 11:36 PM, Kai Tietz <ktietz70@googlemail.com> wrote:
> Hello,
>
> this is the updated version with the suggestion
>
> 2011/10/7 Richard Guenther <richard.guenther@gmail.com>:
>> On Thu, Oct 6, 2011 at 4:25 PM, Kai Tietz <ktietz@redhat.com> wrote:
>>> +      && ((TREE_CODE_CLASS (TREE_CODE (arg1)) != tcc_comparison
>>> +           && TREE_CODE (arg1) != TRUTH_NOT_EXPR
>>> +           && simple_operand_p (arg1))
>>
>> As I said previously simple_operand_p already rejects covers
>> comparisons and TRUTH_NOT_EXPR.  Also arg1 had better
>> TREE_SIDE_EFFECTS set if the comparison might trap, as
>> it might just be hidden in something more complicated - so
>> the simple check isn't enough anyway (and if simple_operand_p
>> would cover it, the check would be better placed there).
>
> I reworked simple_operand_p so that it does this special-casing and additionally
> also checks for trapping.
>
>>> +      if (TREE_CODE (arg0) == code
>>> +          && !TREE_SIDE_EFFECTS (TREE_OPERAND (arg0, 1))
>>> +          && simple_operand_p (TREE_OPERAND (arg0, 1)))
>>> +       {
>>> +         tem = build2_loc (loc,
>>> +                           (code == TRUTH_ANDIF_EXPR ? TRUTH_AND_EXPR
>>> +                                                     : TRUTH_OR_EXPR),
>>> +                           type, TREE_OPERAND (arg0, 1), arg1);
>>> +         return build2_loc (loc, code, type, TREE_OPERAND (arg0, 0),
>>> +                            tem);
>>
>> All trees should be folded, don't use plain build without a good reason.
>
> Ok, done
>
>>> +       }
>>> +      /* Convert X TRUTH-ANDORIF Y to X TRUTH-ANDOR Y, if X and Y
>>> +        are simple operands and have no side-effects.  */
>>> +      if (simple_operand_p (arg0)
>>> +          && !TREE_SIDE_EFFECTS (arg0))
>>
>> Again, the checks you do for arg0 do not match those for arg1.  OTOH
>> it doesn't matter whether arg0 is simple or not or has side-effects or
>> not for this transformation, so why check it at all?
>
> It is required.  For left-hand operand, if it isn't a logical
> and/or/xor, we need to check for side-effects (and for trapping).  I
> see that calling of simple_operand_p is wrong here, as it rejects too
> much.  Nevertheless the check for side-effects is necessary for having
> valid sequence-points.  Without that checking a simple test
>
> int getter (void);
>
> int foo (void)
> {
>  int c, r = 0;
>  while ((c = getter ()) != '"' && c >= 0)
>    r +=c;
>  return r;
> }
>
> would give a warning about sequence-points.  As left-hand operand has
> side-effects, but right-hand not.  If we would combine it as AND, the
> operands are exchange-able.  So right-hand operand needs to be another
> ANDIF expression instead.
> Same apply on trapping.
>
>> In fold_truthop we still have the same (albeit more restricted transform),
>> but guarded with
>>
>>  if (BRANCH_COST (optimize_function_for_speed_p (cfun),
>>                   false) >= 2
>>
>> too.  Why not here?  Please delete redundant code in fold_truthop.
> Well, in general this is the default definition of
> LOGICAL_OP_NON_SHORT_CIRCUIT, so I missed that.  As for some targets
> the macro LOGICAL_OP_NON_SHORT_CIRCUIT might be defined differently,
> it might make sense to check for BRANCH_COST again.
>
>> It's also odd that this is only called from fold_truth_andor but has
>> a more generic name, so maybe rename it to fold_truth_andor_1 on the way.
>
> I renamed it.
>
>> Richard.
>
> ChangeLog
>
> 2011-10-07  Kai Tietz  <ktietz@redhat.com>
>
>        * fold-const.c (simple_operand_p): Make argument non-const
>        and add floating-point trapping check, and special cases for
>        comparisons, and logical-not's.
>        (fold_truthop): Rename to
>        (fold_truth_andor_1): function name.
>        Additionally remove here TRUTH-AND|OR_EXPR generation.
>        (fold_truth_andor): Handle branching at one place.
>
> Bootstrapped and regression-tested for all languages plus Ada and
> Obj-C++ on x86_64-pc-linux-gnu.
> Ok for apply?
>
> Regards,
> 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)));

Clearly wrong.  And what's $$$$ supposed to be?

> +
> +  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;
> +    }
> +

You add a lot of cases here without a good reason.  Why in this patch?
Simply removing the tcc_comparison checks would have been enough ...

>   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

fold_truth_andor

>    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 +8395,52 @@ 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 non-IF branches
> +         together.  Therefore we need to check, if rhs isn't
> +         already an TRUTH_(XOR|OR|AND)[IF]_EXPR.  */

which means, just check if (simple_operand_p (arg0)) ...

> +      if (TREE_CODE (arg0) == code
> +         && TREE_CODE (TREE_OPERAND (arg0, 1)) != TRUTH_AND_EXPR
> +         && TREE_CODE (TREE_OPERAND (arg0, 1)) != TRUTH_OR_EXPR
> +         && TREE_CODE (TREE_OPERAND (arg0, 1)) != TRUTH_XOR_EXPR
> +         && TREE_CODE (TREE_OPERAND (arg0, 1)) != TRUTH_ANDIF_EXPR
> +         && TREE_CODE (TREE_OPERAND (arg0, 1)) != TRUTH_ORIF_EXPR
> +         /* Needed for sequence points and trappings, or side-effects.  */
> +         && !TREE_SIDE_EFFECTS (TREE_OPERAND (arg0, 1))
> +         && !tree_could_trap_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);

Don't do this association here.  Why should it not be applied to
(a TRUTH_ANDIF_EXPR b) TRUTH_AND_EXPR c?  Thus, if you
want to associate the above if b and c do not have side-effects then
do so generally, not only when you are converting a TRUTH_ANDIF_EXPR
to TRUTH_AND_EXPR.

Thus, please remove this association code.

> +       }
> +     else if (TREE_CODE (arg0) != TRUTH_AND_EXPR
> +             && TREE_CODE (arg0) != TRUTH_OR_EXPR
> +             && TREE_CODE (arg0) != TRUTH_ANDIF_EXPR
> +             && TREE_CODE (arg0) != TRUTH_ORIF_EXPR
> +             && TREE_CODE (arg0) != TRUTH_XOR_EXPR
> +             /* Needed for sequence points and trappings, or side-effects.  */
> +             && !TREE_SIDE_EFFECTS (arg0)
> +             && !tree_could_trap_p (arg0))

See above.

You made the patch more complex when I asked for a simpler one.

Richard.

> +       return fold_build2_loc (loc, ncode, type, arg0, arg1);
> +    }
> +
>   return NULL_TREE;
>  }
>
Michael Matz - Oct. 10, 2011, 3:32 p.m.
Hi,

On Mon, 10 Oct 2011, Kai Tietz wrote:

> extern int foo (void); /* foo modifies gbl1 */
> int gbl1 = 0;
> 
> int foo (int ns1)
> {
>   if (ns1 && foo () && gbl1)
>     return 1;
>   return 0;
> }
> 
> so chain of trees has to look like this:
> (ANDIF (ns1 (ANDIF foo () gbl1))

Okay, indeed.  I was wrong when I claimed that only the RHS needs to be 
side-effect-free for ANDIF->AND to be valid.  It's true when the RHS can't 
depend on the LHS, but I only thought about the fact that the side-effect 
must occur, not that it possibly influences RHS.


Ciao,
Michael.

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);