Hello again,
I've been working on several implementations of data layout
optimizations for GCC, and I am again kindly requesting for a review of
the type escape based dead field elimination and field reorg.
Thanks to everyone that has helped me. The main differences between the
previous commits have been fixing the style, adding comments explaining
classes and families of functions, exit gracefully if we handle unknown
gimple syntax, and added a heuristic to handle void* casts.
This patchset is organized in the following way:
* Adds a link-time warning if dead fields are detected
* Allows for the dead-field elimination transformation to be applied
* Reorganizes fields in structures.
* Adds some documentation
* Gracefully does not apply transformation if unknown syntax is detected.
* Adds a heuristic to handle void* casts
I have tested this transformations as extensively as I can. The way to
trigger these transformations are:
-fipa-field-reorder and -fipa-type-escape-analysis
Having said that, I welcome all criticisms and will try to address those
criticisms which I can. Please let me know if you have any questions or
comments, I will try to answer in a timely manner.
The code is in:
refs/vendors/ARM/heads/arm-struct-reorg-wip
Future work includes extending the current heuristic with ipa-modref
extending the analysis to use IPA-PTA as discussed previously.
Few notes:
* Currently it is not safe to use -fipa-sra.
* I added some tests which are now failing by default. This is because
there is no way to safely determine within the test case that a layout
has been transformed. I used to determine that a field was eliminated
doing pointer arithmetic on the fields. And since that is not safe, the
analysis decides not to apply the transformation. There is a way to deal
with this (add a flag to allow the address of a field to be taken) but I
wanted to hear other possibilities to see if there is a better option.
* At this point we’d like to thank the again GCC community for their
patient help so far on the mailing list and in other channels. And we
ask for your support in terms of feedback, comments and testing.
