On Fri, Oct 7, 2011 at 11:36 PM, Kai Tietz <[email protected]> wrote:
> Hello,
>
> this is the updated version with the suggestion
>
> 2011/10/7 Richard Guenther <[email protected]>:
>> On Thu, Oct 6, 2011 at 4:25 PM, Kai Tietz <[email protected]> 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 <[email protected]>
>
> * 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;
> }
>
