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

Kai Tietz ktietz70@googlemail.com
Thu Oct 6 15:00:00 GMT 2011


2011/10/6 Michael Matz <matz@suse.de>:
> Hi,
>
> On Thu, 6 Oct 2011, Richard Guenther wrote:
>
>> > +      && ((TREE_CODE_CLASS (TREE_CODE (arg1)) != tcc_comparison
>> > +          && TREE_CODE (arg1) != TRUTH_NOT_EXPR)
>> > +         || !FLOAT_TYPE_P (TREE_TYPE (TREE_OPERAND (arg1, 0)))))
>>
>> ?  simple_operand_p would have rejected both ! and comparisons.
>>
>> I miss a test for side-effects on arg0 (and probably simple_operand_p there,
>> as well).
>
> He has it in the if() body.  But why?  The point of ANDIF/ORIF is to not
> evaluate the second argument for side-effects when the first argument is
> false/true already, and further to establish an order between both
> evaluations.  The sideeffect on the first arg is always evaluated.
> AND/OR always evaluate both arguments (in unspecified order), but as he
> checks the second one for being free of side effects already that alone is
> already equivalent to ANDIF/ORIF.  No need to check something on the first
> argument.
>
>
> Ciao,
> Michael.


That's not the hole story.  The difference between
TRUTH_(AND|OR)IF_EXPR and TRUTH_(AND|OR)_EXPR are, that for
TRUTH_(AND|OR)IF_EXPR gimplifier creates a COND expression, but for
TRUTH_(AND|OR)_EXPR it doesn't.

Regards,
Kai



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