[BOLT] Match functions with pseudo probes #100446
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Created using spr 1.3.4
Created using spr 1.3.4
Created using spr 1.3.4
Created using spr 1.3.4
…BF, determine best matching binary inline subtrees, find corresponding binary functions, attach the profile to binary function without a profile and most probes Created using spr 1.3.4
Created using spr 1.3.4
Created using spr 1.3.4
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✅ With the latest revision this PR passed the C/C++ code formatter. |
Created using spr 1.3.4
aaupov
added a commit
that referenced
this pull request
Nov 12, 2024
Match inline trees first between profile and the binary: by GUID,
checksum, parent, and inline site for inlined functions. Map profile
probes to binary probes via matched inline tree nodes. Each binary probe
has an associated binary basic block. If all probes from one profile
basic block map to the same binary basic block, it’s an exact match,
otherwise the block is determined by majority vote and reported as loose
match.
Pseudo probe matching happens between exact hash matching and call/loose
matching.
Introduce ProbeMatchSpec - a mechanism to match probes belonging to
another binary function. For example, given functions foo and bar:
```
void foo() {
bar();
}
```
profiled binary: bar is not inlined => have top-level function bar
new binary where the profile is applied to: bar is inlined into foo.
Currently, BOLT does 1:1 matching between profile functions and binary
functions based on the name. #100446 will extend this to N:M where
multiple profiles can be matched to one binary function (as in the
example above where binary function foo would use profiles for foo and
bar), and one profile can be matched to multiple binary functions (e.g.
if bar was inlined into multiple functions).
In this diff, ProbeMatchSpecs would only have one BinaryFunctionProfile
(existing name-based matching).
Test Plan: Added match-blocks-with-pseudo-probes.test
Performance test:
- Setup:
- Baseline no-BOLT: Clang with pseudo probes, ThinLTO + CSSPGO
(#79942)
- BOLT fresh: BOLTed Clang using fresh profile,
- BOLT stale (hash): BOLTed Clang using stale profile (collected on
Clang 10K commits back), `-infer-stale-profile` (hash+call block
matching)
- BOLT stale (+probe): BOLTed Clang using stale profile,
`-infer-stale-profile` with `-stale-matching-with-pseudo-probes`
(hash+call+pseudo probe block matching)
- 2S Intel SKX Xeon 6138 with 40C/80T and 256GB RAM, using 20C/40T for
build,
- BOLT profiles are collected on Clang compiling large preprocessed
C++ file.
- Benchmark: building Clang (average of 5 runs), see driver in
aaupov/llvm-devmtg-2022
- Results, wall time, lower is better:
- Baseline no-BOLT: 429.52 +- 2.61s,
- BOLT stale (hash): 413.21 +- 2.19s,
- BOLT stale (+probe): 409.69 +- 1.41s,
- BOLT fresh: 384.50 +- 1.80s.
---------
Co-authored-by: Amir Ayupov <[email protected]>
Created using spr 1.3.4
This was referenced Oct 28, 2025
Created using spr 1.3.4
Created using spr 1.3.4
aaupov
requested review from
aaupov,
ayermolo,
maksfb,
paschalis-mpeis,
rafaelauler,
yota9 and
yozhu
as code owners
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Extended function and block pseudo probe stale matching
This change brings flexible profile recovery using pseudo probes:
function inlines profile functions,
the profile has more aggressive inlining compared to the input binary.
Prerequisites
--profile-write-pseudo-probesperf2bolt flag.
--stale-matching-with-pseudo-probeswhich augments hash-basedmatching + profile inference enabled with
--infer-stale-profile(required).
-fpseudo-probe-for-profilingClang option.Performance testing
with different profiles causing different inlining decisions,
build,
Depends on:
Co-authored-by: [email protected]