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Re: [RFC] Don't completely scalarize a record if it contains bit-field (PR tree-optimization/45144)


On Mon, Aug 2, 2010 at 6:52 PM, Mark Mitchell <mark@codesourcery.com> wrote:
> Jie Zhang wrote:
>
>> My patch prevents several full scalarizations of records with bit-field
>> when compiling Linux kernel for x86_64, but none of these causes
>> differences in final assemblies. I use 2.6.34.1 and the default config
>> for x86_64. I checked -O2 and -Os.
>
> That seems at odds with the statement made previously in this thread
> that this optimization was essential for Linux kernel performance.
>
> If Jie's statement is accurate, then, whether or not this is a "hack",
> it seems like a win. ?I don't see anything wrong with accepting a small,
> local improvement that has no user-observable negative impact; we can
> always rip it out and replace it with something better when something
> better exists.

OTOH no changes in code generation are also not in favor of this
patch.  Why didn't it improve anything?  Or was that expected?

Can you adjust the patch according to Martins suggestion?

Richard.


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