[PATCH] D69471: [Coverage] Revise format to reduce binary size

[Vedant Kumar via Phabricator via llvm-commits]

vsk created this revision.
vsk added reviewers: ejvaughan, davidxl, arphaman, sajjadm.
Herald added subscribers: llvm-commits, dexonsmith, hiraditya.
Herald added a project: LLVM.

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


https://reviews.llvm.org/D69471

Files:
  clang/include/clang/Basic/DiagnosticFrontendKinds.td
  clang/lib/CodeGen/CoverageMappingGen.cpp
  clang/lib/CodeGen/CoverageMappingGen.h
  clang/test/CoverageMapping/abspath.cpp
  clang/test/CoverageMapping/debug-dir.cpp
  clang/test/CoverageMapping/ir.c
  clang/test/Profile/def-assignop.cpp
  clang/test/Profile/def-ctors.cpp
  clang/test/Profile/def-dtors.cpp
  compiler-rt/lib/profile/InstrProfData.inc
  llvm/docs/CoverageMappingFormat.rst
  llvm/include/llvm/ProfileData/Coverage/CoverageMapping.h
  llvm/include/llvm/ProfileData/Coverage/CoverageMappingReader.h
  llvm/include/llvm/ProfileData/Coverage/CoverageMappingWriter.h
  llvm/include/llvm/ProfileData/InstrProfData.inc
  llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
  llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
  llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp
  llvm/lib/ProfileData/Coverage/CoverageMappingWriter.cpp
  llvm/lib/ProfileData/InstrProf.cpp
  llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp
  llvm/test/Instrumentation/InstrProfiling/X86/alloc.ll
  llvm/test/tools/llvm-cov/Inputs/binary-formats.v3.macho64l
  llvm/test/tools/llvm-cov/binary-formats.c
  llvm/unittests/ProfileData/CoverageMappingTest.cpp

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D69471.226560.patch
Type: text/x-patch
Size: 83545 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20191027/fef6a4c5/attachment.bin>