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


Hi,

On Thu, 6 Oct 2011, Richard Guenther wrote:

> > + Â Â Â&& ((TREE_CODE_CLASS (TREE_CODE (arg1)) != tcc_comparison
> > + Â Â Â Â Â&& TREE_CODE (arg1) != TRUTH_NOT_EXPR)
> > + Â Â Â Â || !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.

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