On Wed, Jun 29, 2011 at 3:00 PM, Kai Tietz <[email protected]> wrote:
> ----- Original Message -----
> From: "Kai Tietz" <[email protected]>
> To: "Richard Guenther" <[email protected]>
> Cc: [email protected]
> Sent: Wednesday, June 29, 2011 1:33:30 PM
> Subject: Re: [patch tree-optimization]: Do bitwise operator optimizations for
> X op !X patterns
>
> ----- Original Message -----
> From: "Richard Guenther" <[email protected]>
> To: "Kai Tietz" <[email protected]>
> Cc: [email protected]
> Sent: Wednesday, June 29, 2011 12:14:10 PM
> Subject: Re: [patch tree-optimization]: Do bitwise operator optimizations for
> X op !X patterns
>
> On Tue, Jun 28, 2011 at 5:05 PM, Kai Tietz <[email protected]> wrote:
>> Hello,
>>
>> this patch implements the X op !X patterns within tree-ssa-forwprop.c
>> without using here const-fold routines. Additionally it does some trivial
>> folding for X op X. Implementation
>> also looks through [(type)] X op [(type)] !X, if type of X is integral and
>> precision is suitable
>> for operation.
>>
>> ChangeLog gcc/
>>
>> 2011-06-28 Kai Tietz <[email protected]>
>>
>> * tree-ssa-forwprop.c (operand_precision_onep): New
>> function.
>> (find_possible_not_expr_argument): Likewise.
>> (simplify_bitwise_binary_1): Likewise.
>> (simplify_bitwise_binary): Use simplify_bitwise_binary_1
>> for detecting various X op !X optimizations.
>>
>> ChangeLog gcc/testsuite
>>
>> 2011-06-28 Kai Tietz <[email protected]>
>>
>> * gcc.dg/binop-notand1a.c: New test.
>> * gcc.dg/binop-notand2a.c: New test.
>> * gcc.dg/binop-notand3a.c: New test.
>> * gcc.dg/binop-notand4a.c: New test.
>> * gcc.dg/binop-notand5a.c: New test.
>> * gcc.dg/binop-notand6a.c: New test.
>> * gcc.dg/binop-notor1.c: New test.
>> * gcc.dg/binop-notor2.c: New test.
>> * gcc.dg/binop-notxor1.c: New test.
>> * gcc.dg/binop-notxor2.c: New test.
>>
>> Bootstrapped and regression tested for all languages plus Ada and Obj-C for
>> x86_64-pc-linux-gnu. Ok for apply?
>
> I can't follow the code in find_possible_not_expr_argument or its uses
> at all. Please try to produce patches that look more obvious in what
> they are doing - don't try to solve every testcase you can come up with
> in a single patch. Especially don't write functions like
> find_possible_not_expr_argument which seems to have evolved a lot
> after you wrote the overall function comment.
>
> Thanks,
> Richard.
>
>> Regards,
>> Kai
>>
>
> Well, I added some comments to these functions and renamed the
> find_possible_not_expr_argument function to detect_not_expr_operand, which
> hits its use better.
> The cause for this function is, that there are more then one variant of
> expressing a logical-not and all of them are used.
> This routine simply tries to detect different variants used for not. Eg ~X ==
> !X and (X ^ 1) == !X for integral type of X with precision one. For X with
> integral type, (X == 0) == !X.
>
> The folding for the three different bitwise-operations is pretty easy and it
> makes sense to implement them at once. I see here no good point to separate
> them into different patches. To separate them might even lead to questions
> about abstracting some code-pieces out of the main function.
> I didn't added testcases for all variants I am aware now. Just those, which
> are now handled.
>
> So hope you can read and understand logic of patch better by updated patch.
>
> Regards,
> Kai
>
> I found that in version I've sent there is an unclosed comment. So here is
> updated patch, which additionally simplify some code to ease reading.
Ok, I'm going to comment on a few things in the patch.
+/* Checks if expression has type of one-bit precision, or is result of
+ a known boolean expression. */
+static bool
+operand_precision_onep (tree expr)
+{
+ enum tree_code code;
+ gimple def_stmt;
+
+ do
+ {
+ code = TREE_CODE (expr);
+ if (!INTEGRAL_TYPE_P (TREE_TYPE (expr)))
+ return false;
+ if (TYPE_PRECISION (TREE_TYPE (expr)) == 1)
+ return true;
+ if (code != SSA_NAME)
+ break;
+ def_stmt = SSA_NAME_DEF_STMT (expr);
+ if (!def_stmt || !is_gimple_assign (def_stmt))
+ break;
+ code = gimple_assign_rhs_code (def_stmt);
+ if (!CONVERT_EXPR_CODE_P (code))
+ break;
+ expr = gimple_assign_rhs1 (def_stmt);
+ }
+ while (CONVERT_EXPR_CODE_P (code));
+
+ if (code == TRUTH_NOT_EXPR || TREE_CODE_CLASS (code) == tcc_comparison)
+ return true;
+ return false;
+}
Please don't do arbitrary deep lookups like this. Instead this
function should be
bool
truth_valued_ssa_name_p (tree name)
{
tree type = TREE_TYPE (name);
gimple def_stmt;
if (!INTEGRAL_TYPE_P (type))
return false;
if (TREE_CODE (type) == BOOLEAN_TYPE
|| TYPE_PRECISION (type) == 1)
return true;
def_stmt = SSA_NAME_DEF_STMT (name);
if (is_gimple_assign (def_stmt))
return truth_value_p (gimple_assign_rhs_code (def_stmt));
return false;
}
+static tree
+detect_not_expr_operand (tree name, tree *nexpr)
same, don't do arbitrary deep lookups. Do simple matches by
enumerating them. The code is not followable or easily verifiable
for correctness. Look at how all the code in fold-const.c is written - it's
very easy to follow what is matched and what is produced. This is not
at all the case for your code.
Richard.
> Regards,
> Kai
>
