Commit Graph

161 Commits

Author SHA1 Message Date
Bruno Cardoso Lopes c192d1942e Track shadow modules with a generation counter.
This is a follow up to r321855, closing the gap between our internal shadow
modules implementation and upstream. It has been tested for longer and
provides a better approach for tracking shadow modules. Mostly NFCI.

rdar://problem/23612102

llvm-svn: 321906
2018-01-05 22:13:56 +00:00
Raphael Isemann abc3d04e47 Use the VFS from the CompilerInvocation by default
Summary:
The CompilerInstance should create its default VFS from its CompilerInvocation. Right now the
user has to manually create the VFS before creating the FileManager even though
`-ivfsoverlay file.yaml` was passed via the CompilerInvocation (which is exactly how we worked
around this issue in `FrontendAction.cpp` so far).

This patch uses the invocation's VFS by default and also tests this behavior now from the
point of view of a program that uses the clang API.

Reviewers: benlangmuir, v.g.vassilev

Reviewed By: v.g.vassilev

Subscribers: mgorny, cfe-commits, v.g.vassilev

Differential Revision: https://reviews.llvm.org/D37416

llvm-svn: 313049
2017-09-12 16:54:53 +00:00
Richard Smith 6d9bc278ef Fix ownership of the MemoryBuffer in a FrontendInputFile.
This fixes a possible crash on certain kinds of corrupted AST file, but
checking in an AST file corrupted in just the right way will be a maintenance
nightmare because the format changes frequently.

llvm-svn: 312851
2017-09-09 01:14:04 +00:00
Richard Smith dbafb6c338 Teach ASTReader how to read only the Preprocessor state from an AST file, not the ASTContext state.
We use this when running a preprocessor-only action on an AST file in order to
avoid paying the runtime cost of loading the extra information.

llvm-svn: 306760
2017-06-29 23:23:46 +00:00
Richard Smith f3f846162a Track the set of module maps read while building a .pcm file and reload those when preprocessing from that .pcm file.
llvm-svn: 306628
2017-06-29 02:19:42 +00:00
Richard Smith b4fd6a6141 Remove some redundant setup when preprocessing .pcm files.
Both of these steps are immediately overwritten by the FrontendAction setup.

llvm-svn: 306325
2017-06-26 20:15:21 +00:00
Richard Smith d9259c2f5e Remove 'Filename' parameter from BeginSourceFileAction.
No-one was using this, and it's not meaningful in general -- FrontendActions
can be run on inputs that don't have a corresponding source file. The current
frontend input can be obtained by asking the FrontendAction if any future
action actually needs it.

llvm-svn: 305045
2017-06-09 01:36:10 +00:00
Richard Smith 1893475d95 Retain header search and preprocessing options from AST file when emitting
preprocessed text for an AST file.

llvm-svn: 304756
2017-06-06 00:32:01 +00:00
Richard Smith 27e5aa0892 Factor out and unify emission of "module is unavailable" diagnostics.
Inspired by post-commit review of r304190.

llvm-svn: 304728
2017-06-05 18:57:56 +00:00
Richard Smith ab75597dda Rather than rejecting attempts to run preprocessor-only actions on AST files,
replay the steps taken to create the AST file with the preprocessor-only action
installed to produce preprocessed output.

This can be used to produce the preprocessed text for an existing .pch or .pcm
file.

llvm-svn: 304726
2017-06-05 18:10:11 +00:00
Richard Smith 040e12662a Support lazy stat'ing of files referenced by module maps.
This patch adds support for a `header` declaration in a module map to specify
certain `stat` information (currently, size and mtime) about that header file.
This has two purposes:

- It removes the need to eagerly `stat` every file referenced by a module map.
  Instead, we track a list of unresolved header files with each size / mtime
  (actually, for simplicity, we track submodules with such headers), and when
  attempting to look up a header file based on a `FileEntry`, we check if there
  are any unresolved header directives with that `FileEntry`'s size / mtime and
  perform deferred `stat`s if so.

- It permits a preprocessed module to be compiled without the original files
  being present on disk. The only reason we used to need those files was to get
  the `stat` information in order to do header -> module lookups when using the
  module. If we're provided with the `stat` information in the preprocessed
  module, we can avoid requiring the files to exist.

Unlike most `header` directives, if a `header` directive with `stat`
information has no corresponding on-disk file the enclosing module is *not*
marked unavailable (so that behavior is consistent regardless of whether we've
resolved a header directive, and so that preprocessed modules don't get marked
unavailable). We could actually do this for all `header` directives: the only
reason we mark the module unavailable if headers are missing is to give a
diagnostic slightly earlier (rather than waiting until we actually try to build
the module / load and validate its .pcm file).

Differential Revision: https://reviews.llvm.org/D33703

llvm-svn: 304515
2017-06-02 01:55:39 +00:00
Richard Smith 8b70610494 [modules] When compiling a preprocessed module map, look for headers relative
to the original module map.

Also use the path and name of the original module map when emitting that
information into the .pcm file. The upshot of this is that the produced .pcm
file will track information for headers in their original locations (where the
module was preprocessed), not relative to whatever directory the preprocessed
module map was in when it was built.

llvm-svn: 304346
2017-05-31 20:56:55 +00:00
Reid Kleckner eb00ee07be Give files from #line the characteristics of the current file
This allows #line directives to appear in system headers that have code
that clang would normally warn on. This is compatible with GCC, which is
easy to test by running `gcc -E`.

Fixes PR30752

llvm-svn: 303582
2017-05-22 21:42:58 +00:00
Richard Smith 8128f3327f Add support for building modules from preprocessed source.
To support this, an optional marker "#pragma clang module contents" is
recognized in module map files, and the rest of the module map file from that
point onwards is treated as the source of the module. Preprocessing a module
map produces the input module followed by the marker and then the preprocessed
contents of the module.

Ignoring line markers, a preprocessed module might look like this:

  module A {
    header "a.h"
  }
  #pragma clang module contents
  #pragma clang module begin A
  // ... a.h ...
  #pragma clang module end

The preprocessed output generates line markers, which are not accepted by the
module map parser, so -x c++-module-map-cpp-output should be used to compile
such outputs.

A couple of major parts do not work yet:

1) The files that are listed in the module map must exist on disk, in order to
   build the on-disk header -> module lookup table in the PCM file. To fix
   this, we need the preprocessed output to track the file size and other stat
   information we might use to build the lookup table.

2) Declaration ownership semantics don't work properly yet, since mapping from
   a source location to a module relies on mapping from FileIDs to modules,
   which we can't do if module transitions can occur in the middle of a file.

llvm-svn: 302309
2017-05-05 22:18:51 +00:00
Richard Smith f74d946624 Move functionality for handling module maps as inputs from the -emit-module
action to the general FrontendAction infrastructure.

This permits applying -E, -ast-dump, -fsyntax-only, and so on to a module map
compilation. (The -E form is not currently especially useful yet as there's no
good way to take the output and use it to actually build a module.)

In order to support this, -cc1 now accepts -x <lang>-module-map in all cases
where it accepts -x <lang> for a language we can parse (not ir/ast). And for
uniformity, we also accept -x <lang>-header for all such languages (we used
to reject for cuda and renderscript), and -x <lang>-cpp-output for all such
languages (we used to reject for c, cl, and renderscript).

(None of these new alternatives are accepted by the driver yet, so no
user-visible changes.)

llvm-svn: 301610
2017-04-28 01:49:42 +00:00
Richard Smith 40c0efa515 Refactor frontend InputKind to prepare for treating module maps as a distinct kind of input.
No functionality change intended.

llvm-svn: 301442
2017-04-26 18:57:40 +00:00
Taewook Oh 06b1af5bf1 Use filename in linemarker when compiling preprocessed source (Revised)
Summary:
This is a revised version of D28796. Included test is changed to
resolve the target compatibility issue reported (rL293032).

Reviewers: inglorion, dblaikie, echristo, aprantl, probinson

Reviewed By: inglorion

Subscribers: mehdi_amini, cfe-commits

Differential Revision: https://reviews.llvm.org/D30663

llvm-svn: 297194
2017-03-07 20:20:23 +00:00
David Blaikie ee12322372 Initialize builtins during modular codegen
llvm-svn: 294512
2017-02-08 20:51:11 +00:00
Vassil Vassilev a2c2d94dcb Enable -dump-deserialized-decls and -error-on-deserialized-decl for modules.
llvm-svn: 294359
2017-02-07 21:49:41 +00:00
Diana Picus ac03b4b924 Revert "Use filename in linemarker when compiling preprocessed source"
This reverts commit r293004 because it broke the buildbots with "unknown CPU"
errors. I tried to fix it in r293026, but that broke on Green Dragon with this
kind of error:

error: expected string not found in input
// CHECK: l{{ +}}df{{ +}}*ABS*{{ +}}{{0+}}{{.+}}preprocessed-input.c{{$}}
          ^
<stdin>:2:1: note: scanning from here
/Users/buildslave/jenkins/sharedspace/incremental@2/clang-build/tools/clang/test/Frontend/Output/preprocessed-input.c.tmp.o: file format Mach-O 64-bit x86-64
^
<stdin>:2:67: note: possible intended match here
/Users/buildslave/jenkins/sharedspace/incremental@2/clang-build/tools/clang/test/Frontend/Output/preprocessed-input.c.tmp.o: file format Mach-O 64-bit x86-64

I suppose this means that llvm-objdump doesn't support Mach-O, so the test
should indeed check for linux (but not for x86). I'll leave it to someone that
knows better.

llvm-svn: 293032
2017-01-25 07:27:05 +00:00
David Callahan ae7e0da4f8 Use filename in linemarker when compiling preprocessed source
Summary:
Clang appears to always use name as specified on the command
line, whereas gcc uses the name as specified in the linemarker at the
first line when compiling a preprocessed source. This results mismatch
between two compilers in FILE symbol table entry. This patch makes clang
to resemble gcc's behavior in finding the original source file name and
use it as an input file name.

Even with this patch, values of FILE symbol table entry may still be
different because clang uses dirname+basename for the entry whlie gcc
uses basename only. I'll write a patch for that once this patch is
committed.

Reviewers: dblaikie, inglorion

Reviewed By: inglorion

Subscribers: inglorion, aprantl, bruno

Differential Revision: https://reviews.llvm.org/D28796

llvm-svn: 293004
2017-01-25 01:55:28 +00:00
David Blaikie 41565463bd Move Preprocessor over to std::shared_ptr rather than IntrusiveRefCntPtr
llvm-svn: 291166
2017-01-05 19:48:07 +00:00
Bruno Cardoso Lopes b4d56f1a4f [Frontend] Use vfs for directory iteration while searching PCHs. NFCI
Use the vfs lookup instead of real filesytem and handle the case where
-include-pch is a directory and this dir is searched for a PCH.

llvm-svn: 289459
2016-12-12 19:28:21 +00:00
John Brawn 4d79ec7fe8 Reapply r276973 "Adjust Registry interface to not require plugins to export a registry"
This differs from the previous version by being more careful about template
instantiation/specialization in order to prevent errors when building with
clang -Werror. Specifically:
 * begin is not defined in the template and is instead instantiated when Head
   is. I think the warning when we don't do that is wrong (PR28815) but for now
   at least do it this way to avoid the warning.
 * Instead of performing template specializations in LLVM_INSTANTIATE_REGISTRY
   instead provide a template definition then do explicit instantiation. No
   compiler I've tried has problems with doing it the other way, but strictly
   speaking it's not permitted by the C++ standard so better safe than sorry.

Original commit message:

Currently the Registry class contains the vestiges of a previous attempt to
allow plugins to be used on Windows without using BUILD_SHARED_LIBS, where a
plugin would have its own copy of a registry and export it to be imported by
the tool that's loading the plugin. This only works if the plugin is entirely
self-contained with the only interface between the plugin and tool being the
registry, and in particular this conflicts with how IR pass plugins work.

This patch changes things so that instead the add_node function of the registry
is exported by the tool and then imported by the plugin, which solves this
problem and also means that instead of every plugin having to export every
registry they use instead LLVM only has to export the add_node functions. This
allows plugins that use a registry to work on Windows if
LLVM_EXPORT_SYMBOLS_FOR_PLUGINS is used.

llvm-svn: 277806
2016-08-05 11:01:08 +00:00
John Brawn 2853269224 Revert r276973 "Adjust Registry interface to not require plugins to export a registry"
Buildbot failures when building with clang -Werror. Reverting while I try to
figure this out.

llvm-svn: 277008
2016-07-28 17:17:22 +00:00
John Brawn 778c3c6c61 Reapply r276856 "Adjust Registry interface to not require plugins to export a registry"
This version has two fixes compared to the original:
 * In Registry.h the template static members are instantiated before they are
   used, as clang gives an error if you do it the other way around.
 * The use of the Registry template in clang-tidy is updated in the same way as
   has been done everywhere else.

Original commit message:

Currently the Registry class contains the vestiges of a previous attempt to
allow plugins to be used on Windows without using BUILD_SHARED_LIBS, where a
plugin would have its own copy of a registry and export it to be imported by
the tool that's loading the plugin. This only works if the plugin is entirely
self-contained with the only interface between the plugin and tool being the
registry, and in particular this conflicts with how IR pass plugins work.

This patch changes things so that instead the add_node function of the registry
is exported by the tool and then imported by the plugin, which solves this
problem and also means that instead of every plugin having to export every
registry they use instead LLVM only has to export the add_node functions. This
allows plugins that use a registry to work on Windows if
LLVM_EXPORT_SYMBOLS_FOR_PLUGINS is used.

llvm-svn: 276973
2016-07-28 12:48:17 +00:00
John Brawn 3839263204 Revert r276856 "Adjust Registry interface to not require plugins to export a registry"
This is causing a huge pile of buildbot failures.

llvm-svn: 276857
2016-07-27 11:41:18 +00:00
John Brawn 63aff61019 Adjust Registry interface to not require plugins to export a registry
Currently the Registry class contains the vestiges of a previous attempt to
allow plugins to be used on Windows without using BUILD_SHARED_LIBS, where a
plugin would have its own copy of a registry and export it to be imported by
the tool that's loading the plugin. This only works if the plugin is entirely
self-contained with the only interface between the plugin and tool being the
registry, and in particular this conflicts with how IR pass plugins work.

This patch changes things so that instead the add_node function of the registry
is exported by the tool and then imported by the plugin, which solves this
problem and also means that instead of every plugin having to export every
registry they use instead LLVM only has to export the add_node functions. This
allows plugins that use a registry to work on Windows if
LLVM_EXPORT_SYMBOLS_FOR_PLUGINS is used.

Differential Revision: http://reviews.llvm.org/D21385

llvm-svn: 276856
2016-07-27 11:18:38 +00:00
Mehdi Amini 9670f847b8 [NFC] Header cleanup
Summary: Removed unused headers, replaced some headers with forward class declarations

Patch by: Eugene <claprix@yandex.ru>

Differential Revision: https://reviews.llvm.org/D20100

llvm-svn: 275882
2016-07-18 19:02:11 +00:00
John Brawn 6c78974b29 Make it possible for AST plugins to enable themselves by default
Currently when an AST plugin is loaded it must then be enabled by passing
-plugin pluginname or -add-plugin pluginname to the -cc1 command line. This
patch adds a method to PluginASTAction which allows it to declare that the
action happens before, instead of, or after the main AST action, plus the
relevant changes to make the plugin action happen at that time automatically.

Differential Revision: http://reviews.llvm.org/D17959

llvm-svn: 263546
2016-03-15 12:51:40 +00:00
Argyrios Kyrtzidis e89a179598 [Frontend] Make sure WrapperFrontendAction updates CurrentInput after calling BeginSourceFileAction.
I don't have a test case to add unfortunately.

llvm-svn: 260937
2016-02-16 05:39:33 +00:00
Argyrios Kyrtzidis d35e98fa91 [Frontend] Make the memory management of FrontendAction pointers explicit by using unique_ptr.
llvm-svn: 260048
2016-02-07 19:28:36 +00:00
Angel Garcia Gomez 637d1e6694 Roll-back r250822.
Summary: It breaks the build for the ASTMatchers

Subscribers: klimek, cfe-commits

Differential Revision: http://reviews.llvm.org/D13893

llvm-svn: 250827
2015-10-20 13:23:58 +00:00
Angel Garcia Gomez b5250d3448 Apply modernize-use-default to clang.
Summary: Replace empty bodies of default constructors and destructors with '= default'.

Reviewers: bkramer, klimek

Subscribers: klimek, alexfh, cfe-commits

Differential Revision: http://reviews.llvm.org/D13890

llvm-svn: 250822
2015-10-20 12:52:55 +00:00
Richard Smith 81c7248cac Fix crash on invalid if we can't find a suitable PCH file in a specified
directory, and our frontend action cares whether the frontend setup actually
succeeded.

llvm-svn: 246881
2015-09-04 21:44:32 +00:00
Adrian Prantl 6b21ab21d1 Add a -gmodules option to the driver and a -dwarf-ext-refs to cc1
to enable the use of external type references in the debug info
(a.k.a. module debugging).

The driver expands -gmodules to "-g -fmodule-format=obj -dwarf-ext-refs"
and passes that to cc1. All this does at the moment is set a flag
codegenopts.

http://reviews.llvm.org/D11958

llvm-svn: 246192
2015-08-27 19:46:20 +00:00
Richard Smith 3938f0c728 [modules] Stop dropping 'module.timestamp' files into the current directory
when building with implicit modules disabled.

llvm-svn: 245136
2015-08-15 00:34:15 +00:00
Eric Christopher 02d5d86b4e Rename the non-coding style conformant functions in namespace Builtins
to match the rest of their brethren and reformat the bits that need it.

llvm-svn: 244186
2015-08-06 01:01:12 +00:00
Adrian Prantl fb2398d0c4 Make the clang module container format selectable from the command line.
- introduces a new cc1 option -fmodule-format=[raw,obj]
  with 'raw' being the default
- supports arbitrary module container formats that libclang is agnostic to
- adds the format to the module hash to avoid collisions
- splits the old PCHContainerOperations into PCHContainerWriter and
  a PCHContainerReader.

Thanks to Richard Smith for reviewing this patch!

llvm-svn: 242499
2015-07-17 01:19:54 +00:00
Adrian Prantl bb165fb04d Introduce a PCHContainerOperations interface (NFC).
A PCHContainerOperations abstract interface provides operations for
creating and unwrapping containers for serialized ASTs (precompiled
headers and clang modules). The default implementation is
RawPCHContainerOperations, which uses a flat file for the output.

The main application for this interface will be an
ObjectFilePCHContainerOperations implementation that uses LLVM to
wrap the module in an ELF/Mach-O/COFF container to store debug info
alongside the AST.

rdar://problem/20091852

llvm-svn: 240225
2015-06-20 18:53:08 +00:00
Duncan P. N. Exon Smith 4a8212a488 Reapply "Frontend: Stop leaking when not -disable-free"
This reverts commit r236422, effectively reapplying r236419.  ASan
helped me diagnose the problem: the non-leaking logic would free the
ASTConsumer before freeing Sema whenever `isCurrentASTFile()`, causing a
use-after-free in `Sema::~Sema()`.

This version unconditionally frees Sema and the ASTContext before
freeing the ASTConsumer.  Without the fix, these were either being freed
before the ASTConsumer was freed or leaked after, but they were always
spiritually released so this isn't really a functionality change.

I ran all of check-clang with ASan locally this time, so I'm hoping
there aren't any more problems lurking.

Original commit message:

    Try again to plug a leak that's been around since at least r128011
    after coming across the FIXME.  Nico Weber tried something similar
    in r207065 but had to revert in r207070 due to a bot failure.

    The build failure isn't visible anymore so I'm not sure what went
    wrong.  I'm doing this slightly differently -- when not
    -disable-free I'm still resetting the members (just not leaking
    them) -- so maybe it will work out this time?  Tests pass locally,
    anyway.

llvm-svn: 236424
2015-05-04 14:59:20 +00:00
Duncan P. N. Exon Smith 20f0b01a92 Revert "Frontend: Stop leaking when not -disable-free"
This reverts commit r236419, since it caused some bots to fail.  On:

http://lab.llvm.org:8011/builders/clang-hexagon-elf/builds/26124
http://bb.pgr.jp/builders/cmake-clang-x86_64-linux/builds/35086

these tests:

FAIL: Clang::import-decl.cpp
FAIL: Clang::floating-literal.c
FAIL: Clang::x86_64-linux-android.c

fail with this output:

Command Output (stderr):
--
Stack dump:
0.  Program arguments: /var/lib/buildbot/slaves/hexagon-build-03/clang-hexagon-elf/llvm.obj/Release+Asserts/bin/clang -cc1 -internal-isystem /var/lib/buildbot/slaves/hexagon-build-03/clang-hexagon-elf/llvm.obj/Release+Asserts/bin/../lib/clang/3.7.0/include -nostdsysteminc -ast-print -x ast -
/var/lib/buildbot/slaves/hexagon-build-03/clang-hexagon-elf/llvm.obj/tools/clang/test/Modules/Output/import-decl.cpp.script: line 3:  9665 Segmentation fault      (core dumped) /var/lib/buildbot/slaves/hexagon-build-03/clang-hexagon-elf/llvm.obj/Release+Asserts/bin/clang -cc1 -internal-isystem /var/lib/buildbot/slaves/hexagon-build-03/clang-hexagon-elf/llvm.obj/Release+Asserts/bin/../lib/clang/3.7.0/include -nostdsysteminc -ast-print -x ast - < /var/lib/buildbot/slaves/hexagon-build-03/clang-hexagon-elf/llvm.obj/tools/clang/test/Modules/Output/import-decl.cpp.tmp.ast
      9666 Done                    | /var/lib/buildbot/slaves/hexagon-build-03/clang-hexagon-elf/llvm.obj/Release+Asserts/bin/FileCheck /var/lib/buildbot/slaves/hexagon-build-03/clang-hexagon-elf/llvm.src/tools/clang/test/Modules/import-decl.cpp

--

llvm-svn: 236422
2015-05-04 13:01:42 +00:00
Duncan P. N. Exon Smith fa4de125c9 Frontend: Stop leaking when not -disable-free
Try again to plug a leak that's been around since at least r128011 after
coming across the FIXME.  Nico Weber tried something similar in r207065
but had to revert in r207070 due to a bot failure.

The build failure isn't visible anymore so I'm not sure what went wrong.
I'm doing this slightly differently -- when not -disable-free I'm still
resetting the members (just not leaking them) -- so maybe it will work
out this time?  Tests pass locally, anyway.

llvm-svn: 236419
2015-05-04 12:36:56 +00:00
Richard Smith 66a8186ed4 Rename MacroDefinition -> MacroDefinitionRecord, Preprocessor::MacroDefinition -> MacroDefinition.
clang::MacroDefinition now models the currently-defined value of a macro. The
previous MacroDefinition type, which represented a record of a macro definition
directive for a detailed preprocessing record, is now called MacroDefinitionRecord.

llvm-svn: 236400
2015-05-04 02:25:31 +00:00
Alexander Kornienko 34eb20725d Use 'override/final' instead of 'virtual' for overridden methods
Summary:
The patch is generated using clang-tidy misc-use-override check.

This command was used:

  tools/clang/tools/extra/clang-tidy/tool/run-clang-tidy.py \
    -checks='-*,misc-use-override' -header-filter='llvm|clang' -j=32 -fix

Reviewers: dblaikie

Reviewed By: dblaikie

Subscribers: klimek, cfe-commits

Differential Revision: http://reviews.llvm.org/D8926

llvm-svn: 234678
2015-04-11 02:00:23 +00:00
Yaron Keren 92e1b62d45 Remove many superfluous SmallString::str() calls.
Now that SmallString is a first-class citizen, most SmallString::str()
calls are not required. This patch removes a whole bunch of them, yet
there are lots more.

There are two use cases where str() is really needed:
1) To use one of StringRef member functions which is not available in
SmallString.
2) To convert to std::string, as StringRef implicitly converts while 
SmallString do not. We may wish to change this, but it may introduce
ambiguity.

llvm-svn: 232622
2015-03-18 10:17:07 +00:00
Argyrios Kyrtzidis bd0b651bd2 [PCH/Modules] Check that the specific module cache path the PCH was built with, is the same as
the one in the current compiler invocation. If they differ reject the PCH.

This protects against the badness occurring from getting modules loaded from different module caches (see crashes).

rdar://19889860

llvm-svn: 229909
2015-02-19 20:12:20 +00:00
Richard Smith ac425e9165 PR22299: Relocate code for handling -fmodule-map-file= so that we don't try to
produce diagnostics with source locations before the diagnostics system is
ready for them.

llvm-svn: 226882
2015-01-23 00:01:13 +00:00
Richard Smith d4b230b378 [modules] Load .pcm files specified by -fmodule-file lazily.
llvm-svn: 220731
2014-10-27 23:01:16 +00:00
Richard Smith e842a47452 [modules] Initial support for explicitly loading .pcm files.
Implicit module builds are not well-suited to a lot of build systems. In
particular, they fare badly in distributed build systems, and they lead to
build artifacts that are not tracked as part of the usual dependency management
process. This change allows explicitly-built module files (which are already
supported through the -emit-module flag) to be explicitly loaded into a build,
allowing build systems to opt to manage module builds and dependencies
themselves.

This is only the first step in supporting such configurations, and it should
be considered experimental and subject to change or removal for now.

llvm-svn: 220359
2014-10-22 02:05:46 +00:00