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dd1ea9de2e
Try again with an up-to-date version of D69471 (99317124 was a stale
revision).
---
Revise the coverage mapping format to reduce binary size by:
1. Naming function records and marking them `linkonce_odr`, and
2. Compressing filenames.
This shrinks the size of llc's coverage segment by 82% (334MB -> 62MB)
and speeds up end-to-end single-threaded report generation by 10%. For
reference the compressed name data in llc is 81MB (__llvm_prf_names).
Rationale for changes to the format:
- With the current format, most coverage function records are discarded.
E.g., more than 97% of the records in llc are *duplicate* placeholders
for functions visible-but-not-used in TUs. Placeholders *are* used to
show under-covered functions, but duplicate placeholders waste space.
- We reached general consensus about giving (1) a try at the 2017 code
coverage BoF [1]. The thinking was that using `linkonce_odr` to merge
duplicates is simpler than alternatives like teaching build systems
about a coverage-aware database/module/etc on the side.
- Revising the format is expensive due to the backwards compatibility
requirement, so we might as well compress filenames while we're at it.
This shrinks the encoded filenames in llc by 86% (12MB -> 1.6MB).
See CoverageMappingFormat.rst for the details on what exactly has
changed.
Fixes PR34533 [2], hopefully.
[1] http://lists.llvm.org/pipermail/llvm-dev/2017-October/118428.html
[2] https://bugs.llvm.org/show_bug.cgi?id=34533
Differential Revision: https://reviews.llvm.org/D69471
These are tests for instrumentation based profiling. This specifically means the -fprofile-instr-generate and -fprofile-instr-use driver flags. Tests in this directory should usually test both: - the generation of instrumentation (-fprofile-instr-generate), and - the use of profile data from instrumented runs (-fprofile-instr-use). In order to test -fprofile-instr-use without actually running an instrumented program, .profdata files are checked into Inputs/. The input source files must include a main function such that building with -fprofile-instr-generate and running the resulting program generates the same .profdata file that is consumed by the tests for -fprofile-instr-use. Even tests that only check -fprofile-instr-use should include such a main function, so that profile data can be regenerated as the .profdata file format evolves.