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Re: [PATCH] Add comments to struct cgraph_thunk_info
On 09/14/2017 07:16 PM, Jeff Law wrote:
The comment additions are fine. What's the rationale behind the
ordering of the fields? In general we want the opposite order from what
you did -- going from most strictly aligned to least strictly aligned
minimizes the amount of unused padding.
Thank you for the review!
I moved them because I thought it would make more sense to readers: flag
that describe the “shape” of the thunk, and then the associated data,
whose validity depends on the flags. I also thought that in practice,
cgraph_thunk_info is embedded only in the cgraph_node class, and the
field after “thunk” (“count”, a profile_count class) must be aligned at
least on 8 bytes (because of n_bits/m_quality), so this change would not
matter structure-size-wise.
I’m not super confident about this though, so I’ll resubmit a patch
without the reordering: I’ve added more comments anyway as I’ve learned
more about this since yesterday. ;-)
--
Pierre-Marie de Rodat