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Re: [whopr] Design/implementation alternatives for the driver and WPA
Chris Lattner <clattner@apple.com> writes:
> On Jun 5, 2008, at 2:03 PM, Ian Lance Taylor wrote:
>
>> Nick Kledzik <kledzik@apple.com> writes:
>>
>>>> How does the linker tell LTO that a symbol may be inlined, but must
>>>> also be externally visible?
>>> The linker just tells LTO which symbols must remain. The LTO engine
>>> is free to inline anything that would improve codegen, with the
>>> exception
>>> that any weak definition that must remain (preserved) cannot be
>>> inlined.
>>
>> I'll just note that that isn't optimal for ELF when producing an
>> executable.
>
> Why? Because you have to touch (worst case) every symbol? The cost of
> doing LTO *dramatically* dwarfs the cost of touching symbols once.
> :) You're right this could be improved, and we're actively working
> on it... but it seems like a strange thing to worry about vs
> correctness in all cases.
Whoops, sorry, I meant the other thing. Not inlining any weak
definition that must remain is not optimal. When linking an
executable, it is perfectly OK to inline a weak function, even if the
weak symbol is required to remain in the final output file. In
general if the symbol is known to be bound locally, then it is OK to
inline it. This is separate from the question of whether the symbol
is visible externally.
Ian