On Tue, Aug 2, 2011 at 3:14 PM, Kai Tietz <ktiet...@googlemail.com> wrote:
> 2011/8/2 Richard Guenther <richard.guent...@gmail.com>:
>> On Tue, Aug 2, 2011 at 12:17 PM, Kai Tietz <ktiet...@googlemail.com> wrote:
>>> Hello,
>>>
>>> this patch removes in forward-propagation useless comparisons X != 0
>>> and X != ~0 for boolean-typed X. For one-bit precision typed X we
>>> simplifiy X == 0 (and X != ~0) to ~X, and for X != 0 (and X == ~0) to
>>> X.
>>> For none one-bit precisione typed X, we simplify here X == 0 -> X ^ 1,
>>> and for X != 0 -> X. We can do this as even for Ada - which has only
>>> boolean-type with none-one-bit precision - the truth-value is one.
>>
>> This isn't a simplification but a canonicalization and thus should be
>> done by fold_stmt instead (we are not propagating anything after all).
>> In fact, fold_stmt should do parts of this already by means of its
>> canonicalizations via fold.
>
> Well, it simplifies and canonicalizes. But to put this into
> gimple-fold looks better.
>
>>> Additionally this patch changes for function
>>> forward_propagate_comparison the meaning of true-result. As this
>>> result wasn't used and it is benefitial to use this propagation also
>>
>> which is a bug - for a true return value we need to set cfg_changed to true.
>
> I addressed this in my updated patch (see below)
>
>>> in second loop in function ssa_forward_propagate_and_combine, it
>>> returns true iff statement was altered. Additionally this function
>>> handles now the boolean-typed simplifications.
>>
>> why call it twice? How should that be "beneficial"? I think that
>> forward_propagate_into_comparison should instead fold the changed
>> statement.
>
> Well, due missing fold_stmt call, there were still none-converted
> comparisons. I've added here the call to fold_stmt_inplace, and it
> solved the issue.
>
>>> For the hunk in gimple.c for function canonicalize_cond_expr_cond:
>>> This change seems to show no real effect, but IMHO it makes sense to
>>> add here the check for cast from boolean-type to be consitant.
>>
>> Probably yes.
>>
>> Thanks,
>> Richard.
>
>
> 2011-08-02 Kai Tietz <kti...@redhat.com>
>
> * gimple.c (canonicalize_cond_expr_cond): Handle cast from boolean-type.
> (ssa_forward_propagate_and_combine): Interprete result of
> forward_propagate_comparison.
> * gcc/gimple-fold.c (fold_gimple_assign): Add canonicalization for
> boolean-typed operands for comparisons.
>
> 2011-08-02 Kai Tietz <kti...@redhat.com>
>
> * gcc.dg/tree-ssa/forwprop-15.c: New testcase.
>
> Regression tested and bootstrapped for all languages (including Ada
> and Obj-C++). Ok for apply?
Comments below
> Regards,
> Kai
>
> Index: gcc/gcc/testsuite/gcc.dg/tree-ssa/forwprop-15.c
> ===================================================================
> --- /dev/null
> +++ gcc/gcc/testsuite/gcc.dg/tree-ssa/forwprop-15.c
> @@ -0,0 +1,14 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-forwprop1" } */
> +
> +_Bool
> +foo (_Bool a, _Bool b, _Bool c
> +{
> + _Bool r1 = a == 0 & b != 0;
> + _Bool r2 = b != 0 & c == 0;
> + return (r1 == 0 & r2 == 0);
> +}
> +
> +/* { dg-final { scan-tree-dump-times " == " 0 "forwprop1" } } */
> +/* { dg-final { scan-tree-dump-times " != " 0 "forwprop1" } } */
> +/* { dg-final { cleanup-tree-dump "forwprop1" } } */
> Index: gcc/gcc/gimple-fold.c
> ===================================================================
> --- gcc.orig/gcc/gimple-fold.c
> +++ gcc/gcc/gimple-fold.c
> @@ -814,6 +814,34 @@ fold_gimple_assign (gimple_stmt_iterator
> gimple_assign_rhs1 (stmt),
> gimple_assign_rhs2 (stmt));
> }
> + else if (gimple_assign_rhs_code (stmt) == EQ_EXPR
> + || gimple_assign_rhs_code (stmt) == NE_EXPR)
> + {
> + tree op1 = gimple_assign_rhs1 (stmt);
> + tree op2 = gimple_assign_rhs2 (stmt);
> + tree type = TREE_TYPE (op1);
> + if (useless_type_conversion_p (TREE_TYPE (gimple_assign_lhs (stmt)),
> + type)
> + && TREE_CODE (op2) == INTEGER_CST)
first check op2, it's cheaper. put the lhs into a local var to avoid the
excessive long line.
And add a comment what you check here - cost me some 2nd thoguht.
Like
/* Check whether the comparison operands are of the same boolean
type as the result type is. */
> + {
> + gimple s;
> + bool inverted = (gimple_assign_rhs_code (stmt) == EQ_EXPR);
> + if (!integer_zerop (op2))
> + inverted = !inverted;
For non-1-precision bools I believe you can have non-1 and non-0 op2.
So you better explicitly check. The code also isn't too easy to follow,
just enumerating the four cases wouldn't cause too much bloat, no?
> + if (inverted == false)
> + result = op1;
> + else if (TREE_CODE (op1) == SSA_NAME
> + && (s = SSA_NAME_DEF_STMT (op1)) != NULL
> + && is_gimple_assign (s)
> + && gimple_assign_rhs_code (s) == BIT_NOT_EXPR)
You shouldn't do stmt lookups here.
> + result = gimple_assign_rhs1 (s);
> + else
> + result = build1_loc (gimple_location (stmt), BIT_NOT_EXPR,
> type, op1);
What about the non-1-precision booleans? You need to generate
op1 ^ 1 here instead, no?
> +
> + }
> +
> + }
>
> if (!result)
> result = fold_binary_loc (loc, subcode,
> Index: gcc/gcc/tree-ssa-forwprop.c
> ===================================================================
> --- gcc.orig/gcc/tree-ssa-forwprop.c
> +++ gcc/gcc/tree-ssa-forwprop.c
> @@ -469,6 +469,9 @@ forward_propagate_into_comparison (gimpl
> {
> gimple_assign_set_rhs_from_tree (gsi, tmp);
> update_stmt (stmt);
> + if (fold_stmt_inplace (stmt))
> + update_stmt (stmt);
> +
No, we need to update_stmt always as we already did change the stmt.
> if (TREE_CODE (rhs1) == SSA_NAME)
> cfg_changed |= remove_prop_source_from_use (rhs1);
> if (TREE_CODE (rhs2) == SSA_NAME)
> @@ -2407,7 +2410,8 @@ ssa_forward_propagate_and_combine (void)
> }
> else if (TREE_CODE_CLASS (code) == tcc_comparison)
> {
> - forward_propagate_comparison (stmt);
> + if (forward_propagate_comparison (stmt))
> + cfg_changed = true;
> gsi_next (&gsi);
This hunk is ok.
Thanks,
Richard.
> }
> else
>
