[llvm-cov] Add lcov tracefile export format.

Summary:
lcov tracefiles are used by various coverage reporting tools and build
systems (e.g., Bazel). It is a simple text-based format to parse and
more convenient to use than the JSON export format, which needs
additional processing to map regions/segments back to line numbers.

It's a little unfortunate that "text" format is now overloaded to refer
specifically to JSON for export, but I wanted to avoid making any
breaking changes to the UI of the llvm-cov tool at this time.

Patch by Tony Allevato (@allevato).

Reviewers: Dor1s, vsk

Reviewed By: Dor1s, vsk

Subscribers: mgorny, llvm-commits

Differential Revision: https://reviews.llvm.org/D54266

llvm-svn: 346506

1 files changed, 17 insertions, 5 deletions

diff --git a/llvm/docs/CommandGuide/llvm-cov.rst b/llvm/docs/CommandGuide/llvm-cov.rst
index 6f1b6e46c48..71924e997d9 100644
--- a/llvm/docs/CommandGuide/llvm-cov.rst
+++ b/llvm/docs/CommandGuide/llvm-cov.rst
@@ -374,9 +374,15 @@ SYNOPSIS
 DESCRIPTION
 ^^^^^^^^^^^
 
-The :program:`llvm-cov export` command exports regions, functions, expansions,
-and summaries of the coverage of the binaries *BIN*,... using the profile data
-*PROFILE* as JSON. It can optionally be filtered to only export the coverage
+The :program:`llvm-cov export` command exports coverage data of the binaries
+*BIN*,... using the profile data *PROFILE* in either JSON or lcov trace file
+format.
+
+When exporting JSON, the regions, functions, expansions, and summaries of the
+coverage data will be exported. When exporting an lcov trace file, the
+line-based coverage and summaries will be exported.
+
+The exported data can optionally be filtered to only export the coverage
 for the files listed in *SOURCES*.
 
 For information on compiling programs for coverage and generating profile data,
@@ -392,12 +398,18 @@ OPTIONS
  universal binary or to use an architecture that does not match a
  non-universal binary.
 
+.. option:: -format=<FORMAT>
+
+ Use the specified output format. The supported formats are: "text" (JSON),
+ "lcov".
+
 .. option:: -summary-only
 
  Export only summary information for each file in the coverage data. This mode
  will not export coverage information for smaller units such as individual
- functions or regions. The result will be the same as produced by :program:
- `llvm-cov report` command, but presented in JSON format rather than text.
+ functions or regions. The result will contain the same information as produced
+ by the :program:`llvm-cov report` command, but presented in JSON or lcov
+ format rather than text.
 
 .. option:: -ignore-filename-regex=<PATTERN>