Discussion:
[PATCH gold/21066] Consider C++ exception handling metadata during ICF
(too old to reply)
Joshua Oreman
2018-09-24 23:12:19 UTC
Permalink
Two functions with the same code might not be combinable during ICF if
they have different C++ exception handling metadata. PR gold/21066
demonstrates this for the case where only the LSDA differs. New
optimizations in GCC 8 can also create cases where the code is
identical but the unwind tables differ; see gold/23482 for more
details. This patch extends ICF to consider a function's associated
FDE and CIE, including any relocations therein (e.g. to the LSDA),
when deciding whether two functions are identical or not.

2018-09-24 Joshua Oreman <***@hudson-trading.com>

PR gold/21066
* gc.h (gc_process_relocs): Track relocations in .eh_frame sections
when ICF is enabled, even though the .eh_frame sections themselves
are not foldable.
* icf.cc (get_section_contents): Change arguments to permit operation
on just part of a section. Include extra identity regions in the
referring section's contents recursively.
(match_sections): Lock object here instead of in get_section_contents
so that get_section_contents can operate recursively.
(Icf::add_ehframe_links): New method.
(Icf::find_identical_sections): Pass .eh_frame sections to
add_ehframe_links(). Increase default iteration count from 2 to 3
because handling exception info typically requires one extra iteration.
* icf.h (Icf::extra_identity_list_): New data member with accessor.
(is_section_foldable_candidate): Include .gcc_except_table sections.
* options.h: Update documentation for new default ICF iteration count.
* testsuite/Makefile.am (icf_test_pr21066): New test case.
* testsuite/Makefile.in: Regenerate.
* testsuite/icf_test_pr21066.cc: New source file.
* testsuite/icf_test_pr21066.sh: New test script.
Cary Coutant
2018-10-02 23:35:43 UTC
Permalink
Post by Joshua Oreman
Two functions with the same code might not be combinable during ICF if
they have different C++ exception handling metadata. PR gold/21066
demonstrates this for the case where only the LSDA differs. New
optimizations in GCC 8 can also create cases where the code is
identical but the unwind tables differ; see gold/23482 for more
details. This patch extends ICF to consider a function's associated
FDE and CIE, including any relocations therein (e.g. to the LSDA),
when deciding whether two functions are identical or not.
Thanks for the patch!

Before I can review it, however, we need a copyright assignment on
file with FSF. I looked, but didn't find one for you or your company.
Would you be willing to assign the copyright to the Free Software
Foundation? If so, I can send you the instructions for taking care of
that.

-cary
Joshua Oreman
2018-10-02 23:57:15 UTC
Permalink
Yes, I'd be happy to do so, I just wasn't familiar with the procedure.
Could you send me the relevant details off-list?

Thanks,
Josh
Post by Cary Coutant
Post by Joshua Oreman
Two functions with the same code might not be combinable during ICF if
they have different C++ exception handling metadata. PR gold/21066
demonstrates this for the case where only the LSDA differs. New
optimizations in GCC 8 can also create cases where the code is
identical but the unwind tables differ; see gold/23482 for more
details. This patch extends ICF to consider a function's associated
FDE and CIE, including any relocations therein (e.g. to the LSDA),
when deciding whether two functions are identical or not.
Thanks for the patch!
Before I can review it, however, we need a copyright assignment on
file with FSF. I looked, but didn't find one for you or your company.
Would you be willing to assign the copyright to the Free Software
Foundation? If so, I can send you the instructions for taking care of
that.
-cary
Joshua Oreman
2018-11-27 18:36:39 UTC
Permalink
This has finally been processed; could you take a look at the patch now?

Josh
Post by Cary Coutant
Post by Joshua Oreman
Two functions with the same code might not be combinable during ICF if
they have different C++ exception handling metadata. PR gold/21066
demonstrates this for the case where only the LSDA differs. New
optimizations in GCC 8 can also create cases where the code is
identical but the unwind tables differ; see gold/23482 for more
details. This patch extends ICF to consider a function's associated
FDE and CIE, including any relocations therein (e.g. to the LSDA),
when deciding whether two functions are identical or not.
Thanks for the patch!
Before I can review it, however, we need a copyright assignment on
file with FSF. I looked, but didn't find one for you or your company.
Would you be willing to assign the copyright to the Free Software
Foundation? If so, I can send you the instructions for taking care of
that.
-cary
Loading...