RE: [PATCH net-next] drivers/net: Remove boolean comparisons to true/false

Le vendredi 10 février 2012 à 09:32 +0000, David Laight a écrit :

The generated code is particularly horrid for boolean arithmetic.
IIRC:
   bool_var &= bool_var_1;
typically requires a sequence of compare and branch instructions.

I suggest you try to upgrade your old compiler and/or always check your
assertions before posting on netdev such claims.

	bool_var &= bool_var_1;

generates a single AND instruction, no compare, no branch.
It would be a failure from compiler optimizer if that was the case.

And (bool_var ? 1 : 0) or (!!bool_var) are NOP for a compiler as well.

(Only one movzbl instruction to convert a byte to a word if context
requires this)

Only difference for bool or unsigned int vars is type promotion, and
fact that compiler knows that 'bool' only can be 0 or 1, so allows more
optimisations than plain "unsigned int".

Really, bools are not evil if well used.


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