llvm-project/clang
Volodymyr Sapsai f91b6f8159 [Modules] Fix rebuilding an updated module for each of its consumers.
Marking a module for a rebuild when its signature differs from the
expected one causes redundant module rebuilds for incremental builds.
When a module is updated, its signature changes. But its consumers still
have the old signature and loading them will result in signature
mismatches. It will correctly cause the rebuilds for the consumers but
we don't need to rebuild the common module for each of them as it is
already up to date.

In practice this bug causes longer build times. We are doing more work
than required and only a single process can build a module, so parallel
builds degrade to a single-process mode where extra processes are just
waiting on a file lock.

Fix by not marking a module dependency for a rebuild on signature
mismatch. We'll check if it is up to date when we load it.

rdar://problem/50212358

Reviewers: dexonsmith, bruno, rsmith

Reviewed By: dexonsmith, bruno

Subscribers: jkorous, ributzka, cfe-commits, aprantl

Differential Revision: https://reviews.llvm.org/D66907

llvm-svn: 370274
2019-08-28 23:31:32 +00:00
..
INPUTS
bindings [clang][Tooling] Infer target and mode from argv[0] when using JSONCompilationDatabase 2019-06-26 07:39:03 +00:00
cmake [CMake][Fuchsia] Define asan+noexcept multilib 2019-07-13 08:07:10 +00:00
docs [ReleaseNotes] MemorySanitizer support of ASLR on FreeBSD 2019-08-27 10:04:03 +00:00
examples Fixup build of clang-interpreter example after change in r370122. 2019-08-28 02:13:24 +00:00
include [analyzer] Fix analyzer warnings on analyzer. 2019-08-28 18:44:38 +00:00
lib [Modules] Fix rebuilding an updated module for each of its consumers. 2019-08-28 23:31:32 +00:00
runtime [GWP-ASan] Mutex implementation [2]. 2019-05-30 19:45:32 +00:00
test [Modules] Fix rebuilding an updated module for each of its consumers. 2019-08-28 23:31:32 +00:00
tools [Clang][Bundler] Do not require host triple for extracting device bundles 2019-08-28 01:26:13 +00:00
unittests ArrayRef'ized CompilerInvocation::CreateFromArgs 2019-08-27 22:13:31 +00:00
utils [OpenCL] Microoptimize OCL2Qual a bit 2019-08-24 13:04:34 +00:00
www Testing commit access; NFC 2019-08-27 12:36:25 +00:00
.arcconfig
.clang-format
.clang-tidy
.gitignore
CMakeLists.txt [CMake] Don't set Python_ADDITIONAL_VERSIONS 2019-07-18 15:17:42 +00:00
CODE_OWNERS.TXT
INSTALL.txt
LICENSE.TXT
ModuleInfo.txt
NOTES.txt
README.txt [NFC] Test commit 2019-06-12 07:50:48 +00:00

README.txt

//===----------------------------------------------------------------------===//
// C Language Family Front-end
//===----------------------------------------------------------------------===//

Welcome to Clang.  This is a compiler front-end for the C family of languages
(C, C++, Objective-C, and Objective-C++) which is built as part of the LLVM
compiler infrastructure project.

Unlike many other compiler frontends, Clang is useful for a number of things
beyond just compiling code: we intend for Clang to be host to a number of
different source-level tools.  One example of this is the Clang Static Analyzer.

If you're interested in more (including how to build Clang) it is best to read
the relevant web sites.  Here are some pointers:

Information on Clang:             http://clang.llvm.org/
Building and using Clang:         http://clang.llvm.org/get_started.html
Clang Static Analyzer:            http://clang-analyzer.llvm.org/
Information on the LLVM project:  http://llvm.org/

If you have questions or comments about Clang, a great place to discuss them is
on the Clang development mailing list:
  http://lists.llvm.org/mailman/listinfo/cfe-dev

If you find a bug in Clang, please file it in the LLVM bug tracker:
  http://llvm.org/bugs/