From dd1ea9de2e3e3ac80a620f71411a9a36449f2697 Mon Sep 17 00:00:00 2001 From: Vedant Kumar Date: Mon, 21 Oct 2019 11:48:38 -0700 Subject: Reland: [Coverage] Revise format to reduce binary size 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 --- llvm/lib/ProfileData/Coverage/CoverageMapping.cpp | 2 ++ 1 file changed, 2 insertions(+) (limited to 'llvm/lib/ProfileData/Coverage/CoverageMapping.cpp') diff --git a/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp b/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp index 9d39b7c..70f00d3 100644 --- a/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp +++ b/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp @@ -805,6 +805,8 @@ static std::string getCoverageMapErrString(coveragemap_error Err) { return "Truncated coverage data"; case coveragemap_error::malformed: return "Malformed coverage data"; + case coveragemap_error::decompression_failed: + return "Failed to decompress coverage data (zlib)"; } llvm_unreachable("A value of coveragemap_error has no message."); } -- cgit v1.1