* [Bug default/27568] New: Add initial .debug_info reading phase to dwz
@ 2021-03-12 10:54 vries at gcc dot gnu.org
2021-03-12 10:56 ` [Bug default/27568] " vries at gcc dot gnu.org
0 siblings, 1 reply; 2+ messages in thread
From: vries at gcc dot gnu.org @ 2021-03-12 10:54 UTC (permalink / raw)
To: dwz
https://sourceware.org/bugzilla/show_bug.cgi?id=27568
Bug ID: 27568
Summary: Add initial .debug_info reading phase to dwz
Product: dwz
Version: unspecified
Status: NEW
Severity: enhancement
Priority: P2
Component: default
Assignee: nobody at sourceware dot org
Reporter: vries at gcc dot gnu.org
CC: dwz at sourceware dot org
Target Milestone: ---
Currently dwz is setup such that the .debug_info section is read once (unless
we have low-mem mode).
There is a number of problems with this approach.
I. Forward (pseudo) references.
When encountering a reference, and it's intra-CU or backward inter-CU, we can
determine whether the reference is to an actual DIE or not, because we've
already processed those DIEs and they're in the off_htab. But when encountering
a forward inter-CU reference, we don't known, because those DIEs haven't been
processed yet. See PR25459 for a pseudo-reference example.
If in all cases we can determine whether a DIE reference is valid or not, we
can handle the invalid ones more gracefully: assume a value of 0 and continue
processing (PR27544).
II. Input error messages are generated on-the-fly (PR 25229)
Input errors are generated when and where they are encountered.
- it may take a long while to find out that we cannot optimize the file.
- the error messages are not deterministic. An unrelated change in input
may influence whether the error is triggered or not.
- the errors may have to be handled in more than one location in the source
code
III. Sub-file level parallelization (PR27557)
Things that can and cannot be parallelized are interwoven in the
implementation. If we'd have two phases or reading .debug_info instead of
one, we could try to move non-parallelizable to the first phase, and
parallelizable parts to the second phase, as well as detect
parallelization-breaking conditions in the first phase.
IV. Ad-hoc determination of optimization scope
Computation of optimization scope (i.e, propagation of CK_BAD,
die_no_multifile) is done in parallel with the optimization. Some of this
propagation is backwards, and needs to be fixed up after optimization to get
propagation complete (see propagate_multifile, PR25109), which is awkward.
Also, for odr we have the inelegant and expensive solution of calling
checksum_ref_die twice (PR26252), once to do the CK_BAD propagation, which
gives us wrong checksums for the odr DIEs, which we then fixup, after which we
call checksum_ref_die again, to recalculate the checksums for the non-odr DIEs.
If the CK_BAD propagation was separated from the checksum calculation, we
wouldn't have to redo the checksum calculation for non-odr DIEs.
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* [Bug default/27568] Add initial .debug_info reading phase to dwz
2021-03-12 10:54 [Bug default/27568] New: Add initial .debug_info reading phase to dwz vries at gcc dot gnu.org
@ 2021-03-12 10:56 ` vries at gcc dot gnu.org
0 siblings, 0 replies; 2+ messages in thread
From: vries at gcc dot gnu.org @ 2021-03-12 10:56 UTC (permalink / raw)
To: dwz
https://sourceware.org/bugzilla/show_bug.cgi?id=27568
Tom de Vries <vries at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Blocks| |27544, 25229, 27557, 25459
Referenced Bugs:
https://sourceware.org/bugzilla/show_bug.cgi?id=25229
[Bug 25229] Add input verification phase
https://sourceware.org/bugzilla/show_bug.cgi?id=25459
[Bug 25459] Forward pseudo-reference triggers error
https://sourceware.org/bugzilla/show_bug.cgi?id=27544
[Bug 27544] [dwz] Handle dwarf errors more graciously
https://sourceware.org/bugzilla/show_bug.cgi?id=27557
[Bug 27557] Use threading at sub-file level
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