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Differential D118499

[docs] Update Prolog/Epilog Code Insertion docs to show it's still incomplete
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Authored by DanielMcIntosh-IBM on Jan 28 2022, 11:24 AM.

Details

Reviewers
void
arsenm
aeubanks
rogfer01
Commits
rG0ee7a2c3046d: [docs] Update Prolog/Epilog Code Insertion docs to show it's still incomplete
Summary

Compact Unwind is a subsection, but that was lost in rGff9feeb520a32d076c3095468208ae116c428285

Diff Detail

Event Timeline

DanielMcIntosh-IBM requested review of this revision.Jan 28 2022, 11:24 AM
DanielMcIntosh-IBM created this revision.
Herald added a project: Restricted Project. · View Herald TranscriptJan 28 2022, 11:24 AM
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DanielMcIntosh-IBM added reviewers: arsenm, aeubanks, rogfer01.Jan 28 2022, 11:38 AM
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DanielMcIntosh-IBM added a comment.Jan 28 2022, 11:47 AM

Not really sure who to add as a reviewer for this. Feel free to add/remove people.

Also: I'm not sure if Compact Unwind even belongs in the Prolog/Epilog Code Insertion section. I don't know very much about it, but it seems to me like it's something entirely separate from Prolog/Epilog Code Insertion.

void accepted this revision.Jan 28 2022, 12:36 PM
In D118499#3280491, @DanielMcIntosh-IBM wrote:

Also: I'm not sure if Compact Unwind even belongs in the Prolog/Epilog Code Insertion section. I don't know very much about it, but it seems to me like it's something entirely separate from Prolog/Epilog Code Insertion.

Good point. This is probably just an oversight. I added a comment to change the heading for "Compact Unwind" to an H1 instead of H2. But otherwise LGTM.

llvm/docs/CodeGenerator.rst
1490

Please change to dashes (e.g. ---).

This revision is now accepted and ready to land.Jan 28 2022, 12:36 PM
Harbormaster completed remote builds in B146343: Diff 404105.Jan 28 2022, 1:10 PM
DanielMcIntosh-IBM updated this revision to Diff 404538.Jan 31 2022, 8:07 AM

As per review comment, change heading level for Compact Unwind so it's no longer under Prolog/Epilog

DanielMcIntosh-IBM updated this revision to Diff 404539.Jan 31 2022, 8:12 AM

No change, rebase so hopefully CI passes this time

Harbormaster completed remote builds in B146646: Diff 404539.Jan 31 2022, 10:10 AM
This revision was landed with ongoing or failed builds.Jan 31 2022, 12:25 PM
Closed by commit rG0ee7a2c3046d: [docs] Update Prolog/Epilog Code Insertion docs to show it's still incomplete (authored by DanielMcIntosh-IBM). · Explain Why
This revision was automatically updated to reflect the committed changes.
DanielMcIntosh-IBM added a commit: rG0ee7a2c3046d: [docs] Update Prolog/Epilog Code Insertion docs to show it's still incomplete.

Revision Contents

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docs/
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Diff 404666

llvm/docs/CodeGenerator.rst

Show First 20 Lines • Show All 1,476 Lines • ▼ Show 20 Lines.. code-block:: bash
$ llc -regalloc=fast file.bc -o fa.s $ llc -regalloc=fast file.bc -o fa.s
$ llc -regalloc=pbqp file.bc -o pbqp.s $ llc -regalloc=pbqp file.bc -o pbqp.s
.. _Prolog/Epilog Code Insertion: .. _Prolog/Epilog Code Insertion:
Prolog/Epilog Code Insertion Prolog/Epilog Code Insertion
---------------------------- ----------------------------
.. note::
To Be Written
Compact Unwind Compact Unwind
--------------
voidUnsubmitted
Not Done
ReplyInline Actions

Please change to dashes (e.g. ---).

void: Please change to dashes (e.g. `---`).
Throwing an exception requires *unwinding* out of a function. The information on Throwing an exception requires *unwinding* out of a function. The information on
how to unwind a given function is traditionally expressed in DWARF unwind how to unwind a given function is traditionally expressed in DWARF unwind
(a.k.a. frame) info. But that format was originally developed for debuggers to (a.k.a. frame) info. But that format was originally developed for debuggers to
backtrace, and each Frame Description Entry (FDE) requires ~20-30 bytes per backtrace, and each Frame Description Entry (FDE) requires ~20-30 bytes per
function. There is also the cost of mapping from an address in a function to the function. There is also the cost of mapping from an address in a function to the
corresponding FDE at runtime. An alternative unwind encoding is called *compact corresponding FDE at runtime. An alternative unwind encoding is called *compact
unwind* and requires just 4-bytes per function. unwind* and requires just 4-bytes per function.
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