2011/10/10 Richard Guenther <richard.guent...@gmail.com>:
> On Mon, Oct 10, 2011 at 2:29 PM, Kai Tietz <ktiet...@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
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;
}
