Re: Proposal: PageLayout footprint

Gregory Stark wrote:
> "Zdenek Kotala" <Zdenek.Kotala@Sun.COM> writes:
>> By my opinion -fipa-struct-reorg GCC option could break structure. And maybe
>> there are more compiler magic switches and optimization on different platforms
>> which can modify structure alignment or member order. It probably does not
>> happen often but footprint should protect people to shot himself.
> 
> My version of GCC doesn't have that option, what does it do?
From gcc man page:

>        -fipa-struct-reorg
>            Perform structure reorganization optimization, that change C-like
>            structures layout in order to better utilize spatial locality.
>            This transformation is affective for programs containing arrays of
>            structures.  Available in two compilation modes: profile-based
>            (enabled with -fprofile-generate) or static (which uses built-in
>            heuristics).  Require -fipa-type-escape to provide the safety of
>            this transformation.  It works only in whole program mode, so it
>            requires -fwhole-program and -combine to be enabled.  Structures
>            considered cold by this transformation are not affected (see
>            --param struct-reorg-cold-struct-ratio=value).

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