This adds some of LLD specific scopes and picks up optimisation scopes
via LTO/ThinLTO. Makes use of TimeProfiler multi-thread support added in
77e6bb3c.
Differential Revision: https://reviews.llvm.org/D71060
This extends the RemarkStreamer to allow for other emitters (e.g.
frontends, SIL, etc.) to emit remarks through a common interface.
See changes in llvm/docs/Remarks.rst for motivation and design choices.
Differential Revision: https://reviews.llvm.org/D73676
This is how it should've been and brings it more in line with
std::string_view. There should be no functional change here.
This is mostly mechanical from a custom clang-tidy check, with a lot of
manual fixups. It uncovers a lot of minor inefficiencies.
This doesn't actually modify StringRef yet, I'll do that in a follow-up.
This restores 59733525d3 (D71913), along
with bot fix 19c76989bb.
The bot failure should be fixed by D73418, committed as
af954e441a.
I also added a fix for non-x86 bot failures by requiring x86 in new test
lld/test/ELF/lto/devirt_vcall_vis_public.ll.
Summary:
Third part in series to support Safe Whole Program Devirtualization
Enablement, see RFC here:
http://lists.llvm.org/pipermail/llvm-dev/2019-December/137543.html
This patch adds type test metadata under -fwhole-program-vtables,
even for classes without hidden visibility. It then changes WPD to skip
devirtualization for a virtual function call when any of the compatible
vtables has public vcall visibility.
Additionally, internal LLVM options as well as lld and gold-plugin
options are added which enable upgrading all public vcall visibility
to linkage unit (hidden) visibility during LTO. This enables the more
aggressive WPD to kick in based on LTO time knowledge of the visibility
guarantees.
Support was added to all flavors of LTO WPD (regular, hybrid and
index-only), and to both the new and old LTO APIs.
Unfortunately it was not simple to split the first and second parts of
this part of the change (the unconditional emission of type tests and
the upgrading of the vcall visiblity) as I needed a way to upgrade the
public visibility on legacy WPD llvm assembly tests that don't include
linkage unit vcall visibility specifiers, to avoid a lot of test churn.
I also added a mechanism to LowerTypeTests that allows dropping type
test assume sequences we now aggressively insert when we invoke
distributed ThinLTO backends with null indexes, which is used in testing
mode, and which doesn't invoke the normal ThinLTO backend pipeline.
Depends on D71907 and D71911.
Reviewers: pcc, evgeny777, steven_wu, espindola
Subscribers: emaste, Prazek, inglorion, arichardson, hiraditya, MaskRay, dexonsmith, dang, davidxl, cfe-commits, llvm-commits
Tags: #clang, #llvm
Differential Revision: https://reviews.llvm.org/D71913
The lto::Config object saved on the global LTO object should not be
updated by any of the LTO backends. Otherwise we could run into
interference between threads utilizing it. Motivated by some proposed
changes that would have caused it to get modified in the ThinLTO
backends.
ValueInfo has user-defined 'operator bool' which allows incorrect implicit conversion
to GlobalValue::GUID (which is unsigned long). This causes bugs which are hard to
track and should be removed in future.
This patch adds an assertion check for exported read/write-only
variables to be also in import list for module. If they aren't
we may face linker errors, because read/write-only variables are
internalized in their source modules. The patch also changes
export lists to store ValueInfo instead of GUID for performance
considerations.
Differential revision: https://reviews.llvm.org/D70128
Remove dead virtual functions from vtables with
replaceNonMetadataUsesWith, so that CGProfile metadata gets cleaned up
correctly.
Original commit message:
Currently, it is hard for the compiler to remove unused C++ virtual
functions, because they are all referenced from vtables, which are referenced
by constructors. This means that if the constructor is called from any live
code, then we keep every virtual function in the final link, even if there
are no call sites which can use it.
This patch allows unused virtual functions to be removed during LTO (and
regular compilation in limited circumstances) by using type metadata to match
virtual function call sites to the vtable slots they might load from. This
information can then be used in the global dead code elimination pass instead
of the references from vtables to virtual functions, to more accurately
determine which functions are reachable.
To make this transformation safe, I have changed clang's code-generation to
always load virtual function pointers using the llvm.type.checked.load
intrinsic, instead of regular load instructions. I originally tried writing
this using clang's existing code-generation, which uses the llvm.type.test
and llvm.assume intrinsics after doing a normal load. However, it is possible
for optimisations to obscure the relationship between the GEP, load and
llvm.type.test, causing GlobalDCE to fail to find virtual function call
sites.
The existing linkage and visibility types don't accurately describe the scope
in which a virtual call could be made which uses a given vtable. This is
wider than the visibility of the type itself, because a virtual function call
could be made using a more-visible base class. I've added a new
!vcall_visibility metadata type to represent this, described in
TypeMetadata.rst. The internalization pass and libLTO have been updated to
change this metadata when linking is performed.
This doesn't currently work with ThinLTO, because it needs to see every call
to llvm.type.checked.load in the linkage unit. It might be possible to
extend this optimisation to be able to use the ThinLTO summary, as was done
for devirtualization, but until then that combination is rejected in the
clang driver.
To test this, I've written a fuzzer which generates random C++ programs with
complex class inheritance graphs, and virtual functions called through object
and function pointers of different types. The programs are spread across
multiple translation units and DSOs to test the different visibility
restrictions.
I've also tried doing bootstrap builds of LLVM to test this. This isn't
ideal, because only classes in anonymous namespaces can be optimised with
-fvisibility=default, and some parts of LLVM (plugins and bugpoint) do not
work correctly with -fvisibility=hidden. However, there are only 12 test
failures when building with -fvisibility=hidden (and an unmodified compiler),
and this change does not cause any new failures for either value of
-fvisibility.
On the 7 C++ sub-benchmarks of SPEC2006, this gives a geomean code-size
reduction of ~6%, over a baseline compiled with "-O2 -flto
-fvisibility=hidden -fwhole-program-vtables". The best cases are reductions
of ~14% in 450.soplex and 483.xalancbmk, and there are no code size
increases.
I've also run this on a set of 8 mbed-os examples compiled for Armv7M, which
show a geomean size reduction of ~3%, again with no size increases.
I had hoped that this would have no effect on performance, which would allow
it to awlays be enabled (when using -fwhole-program-vtables). However, the
changes in clang to use the llvm.type.checked.load intrinsic are causing ~1%
performance regression in the C++ parts of SPEC2006. It should be possible to
recover some of this perf loss by teaching optimisations about the
llvm.type.checked.load intrinsic, which would make it worth turning this on
by default (though it's still dependent on -fwhole-program-vtables).
Differential revision: https://reviews.llvm.org/D63932
llvm-svn: 375094
Currently, it is hard for the compiler to remove unused C++ virtual
functions, because they are all referenced from vtables, which are referenced
by constructors. This means that if the constructor is called from any live
code, then we keep every virtual function in the final link, even if there
are no call sites which can use it.
This patch allows unused virtual functions to be removed during LTO (and
regular compilation in limited circumstances) by using type metadata to match
virtual function call sites to the vtable slots they might load from. This
information can then be used in the global dead code elimination pass instead
of the references from vtables to virtual functions, to more accurately
determine which functions are reachable.
To make this transformation safe, I have changed clang's code-generation to
always load virtual function pointers using the llvm.type.checked.load
intrinsic, instead of regular load instructions. I originally tried writing
this using clang's existing code-generation, which uses the llvm.type.test
and llvm.assume intrinsics after doing a normal load. However, it is possible
for optimisations to obscure the relationship between the GEP, load and
llvm.type.test, causing GlobalDCE to fail to find virtual function call
sites.
The existing linkage and visibility types don't accurately describe the scope
in which a virtual call could be made which uses a given vtable. This is
wider than the visibility of the type itself, because a virtual function call
could be made using a more-visible base class. I've added a new
!vcall_visibility metadata type to represent this, described in
TypeMetadata.rst. The internalization pass and libLTO have been updated to
change this metadata when linking is performed.
This doesn't currently work with ThinLTO, because it needs to see every call
to llvm.type.checked.load in the linkage unit. It might be possible to
extend this optimisation to be able to use the ThinLTO summary, as was done
for devirtualization, but until then that combination is rejected in the
clang driver.
To test this, I've written a fuzzer which generates random C++ programs with
complex class inheritance graphs, and virtual functions called through object
and function pointers of different types. The programs are spread across
multiple translation units and DSOs to test the different visibility
restrictions.
I've also tried doing bootstrap builds of LLVM to test this. This isn't
ideal, because only classes in anonymous namespaces can be optimised with
-fvisibility=default, and some parts of LLVM (plugins and bugpoint) do not
work correctly with -fvisibility=hidden. However, there are only 12 test
failures when building with -fvisibility=hidden (and an unmodified compiler),
and this change does not cause any new failures for either value of
-fvisibility.
On the 7 C++ sub-benchmarks of SPEC2006, this gives a geomean code-size
reduction of ~6%, over a baseline compiled with "-O2 -flto
-fvisibility=hidden -fwhole-program-vtables". The best cases are reductions
of ~14% in 450.soplex and 483.xalancbmk, and there are no code size
increases.
I've also run this on a set of 8 mbed-os examples compiled for Armv7M, which
show a geomean size reduction of ~3%, again with no size increases.
I had hoped that this would have no effect on performance, which would allow
it to awlays be enabled (when using -fwhole-program-vtables). However, the
changes in clang to use the llvm.type.checked.load intrinsic are causing ~1%
performance regression in the C++ parts of SPEC2006. It should be possible to
recover some of this perf loss by teaching optimisations about the
llvm.type.checked.load intrinsic, which would make it worth turning this on
by default (though it's still dependent on -fwhole-program-vtables).
Differential revision: https://reviews.llvm.org/D63932
llvm-svn: 374539
Summary:
This fixes a hole in the handling of devirtualized targets that were
local but need promoting due to devirtualization in another module. We
were not correctly referencing the promoted symbol in some cases. Make
sure the code that updates the name also looks at the ExportedGUIDs set
by utilizing a callback that checks all conditions (the callback
utilized by the internalization/promotion code).
Reviewers: pcc, davidxl, hiraditya
Subscribers: mehdi_amini, Prazek, inglorion, steven_wu, dexonsmith, dang, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D68159
llvm-svn: 373485
Summary:
This is needed to implemented the same approach as lld (implemented in r338434)
for how to handling symbols that can be generated by LTO code generator
but not present in the symbol table for linker that uses legacy C APIs.
libLTO is in charge of providing the list of symbols. Linker is in
charge of implementing the eager loading from static libraries using
the list of symbols.
rdar://problem/52853974
Reviewers: tejohnson, bd1976llvm, deadalnix, espindola
Reviewed By: tejohnson
Subscribers: emaste, arichardson, hiraditya, MaskRay, dang, kledzik, mehdi_amini, inglorion, jkorous, dexonsmith, ributzka, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D67568
llvm-svn: 372021
Summary:
Keep aliasees alive if their alias is live, otherwise we end up with an
alias to a declaration, which is invalid. This can happen when the
aliasee is weak and non-prevailing.
This fix exposed the fact that we were then attempting to internalize
the weak symbol, which was not exported as it was not prevailing. We
should not internalize interposable symbols in general, unless this is
the prevailing copy, since it can lead to incorrect inlining and other
optimizations. Most of the changes in this patch are due to the
restructuring required to pass down the prevailing callback.
Finally, while implementing the test cases, I found that in the case of
a weak aliasee that is still marked not live because its alias isn't
live, after dropping the definition we incorrectly marked the
declaration with weak linkage when resolving prevailing symbols in the
module. This was due to some special case handling for symbols marked
WeakLinkage in the summary located before instead of after a subsequent
check for the symbol being a declaration. It turns out that we don't
actually need this special case handling any more (looking back at the
history, when that was added the code was structured quite differently)
- we will correctly mark with weak linkage further below when the
definition hasn't been dropped.
Fixes PR42542.
Reviewers: pcc
Subscribers: mehdi_amini, inglorion, steven_wu, dexonsmith, dang, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D66264
llvm-svn: 369766
Now that we've moved to C++14, we no longer need the llvm::make_unique
implementation from STLExtras.h. This patch is a mechanical replacement
of (hopefully) all the llvm::make_unique instances across the monorepo.
llvm-svn: 369013
This patch adds support to the WholeProgramDevirt pass to perform
index-based WPD, which is invoked from ThinLTO during the thin link.
The ThinLTO backend (WPD import phase) behaves the same regardless of
whether the WPD decisions were made with the index-based or (the
existing) IR-based analysis.
Depends on D54815.
Reviewers: pcc
Subscribers: mehdi_amini, inglorion, eraman, steven_wu, dexonsmith, arphaman, dang, llvm-commits
Differential Revision: https://reviews.llvm.org/D55153
llvm-svn: 367679
It's possible that some function can load and store the same
variable using the same constant expression:
store %Derived* @foo, %Derived** bitcast (%Base** @bar to %Derived**)
%42 = load %Derived*, %Derived** bitcast (%Base** @bar to %Derived**)
The bitcast expression was mistakenly cached while processing loads,
and never examined later when processing store. This caused @bar to
be mistakenly treated as read-only variable. See load-store-caching.ll.
llvm-svn: 365188
This reverts r365040 (git commit 5cacb91475)
Speculatively reverting, since this appears to have broken check-lld on
Linux. Partial analysis in https://crbug.com/981168.
llvm-svn: 365097
Use -fsave-optimization-record=<format> to specify a different format
than the default, which is YAML.
For now, only YAML is supported.
llvm-svn: 363573
* Add a common function to setup opt-remarks
* Rename common options to the same names
* Add error types to distinguish between file errors and regex errors
llvm-svn: 363415
* Add a common function to setup opt-remarks
* Rename common options to the same names
* Add error types to distinguish between file errors and regex errors
llvm-svn: 363328
Separate the remark serialization to YAML from the LLVM Diagnostics.
This adds a new serialization abstraction: remarks::Serializer. It's
completely independent from lib/IR and it provides an easy way to
replace YAML by providing a new remarks::Serializer.
Differential Revision: https://reviews.llvm.org/D62632
llvm-svn: 362160
This patch implements a limited form of autolinking primarily designed to allow
either the --dependent-library compiler option, or "comment lib" pragmas (
https://docs.microsoft.com/en-us/cpp/preprocessor/comment-c-cpp?view=vs-2017) in
C/C++ e.g. #pragma comment(lib, "foo"), to cause an ELF linker to automatically
add the specified library to the link when processing the input file generated
by the compiler.
Currently this extension is unique to LLVM and LLD. However, care has been taken
to design this feature so that it could be supported by other ELF linkers.
The design goals were to provide:
- A simple linking model for developers to reason about.
- The ability to to override autolinking from the linker command line.
- Source code compatibility, where possible, with "comment lib" pragmas in other
environments (MSVC in particular).
Dependent library support is implemented differently for ELF platforms than on
the other platforms. Primarily this difference is that on ELF we pass the
dependent library specifiers directly to the linker without manipulating them.
This is in contrast to other platforms where they are mapped to a specific
linker option by the compiler. This difference is a result of the greater
variety of ELF linkers and the fact that ELF linkers tend to handle libraries in
a more complicated fashion than on other platforms. This forces us to defer
handling the specifiers to the linker.
In order to achieve a level of source code compatibility with other platforms
we have restricted this feature to work with libraries that meet the following
"reasonable" requirements:
1. There are no competing defined symbols in a given set of libraries, or
if they exist, the program owner doesn't care which is linked to their
program.
2. There may be circular dependencies between libraries.
The binary representation is a mergeable string section (SHF_MERGE,
SHF_STRINGS), called .deplibs, with custom type SHT_LLVM_DEPENDENT_LIBRARIES
(0x6fff4c04). The compiler forms this section by concatenating the arguments of
the "comment lib" pragmas and --dependent-library options in the order they are
encountered. Partial (-r, -Ur) links are handled by concatenating .deplibs
sections with the normal mergeable string section rules. As an example, #pragma
comment(lib, "foo") would result in:
.section ".deplibs","MS",@llvm_dependent_libraries,1
.asciz "foo"
For LTO, equivalent information to the contents of a the .deplibs section can be
retrieved by the LLD for bitcode input files.
LLD processes the dependent library specifiers in the following way:
1. Dependent libraries which are found from the specifiers in .deplibs sections
of relocatable object files are added when the linker decides to include that
file (which could itself be in a library) in the link. Dependent libraries
behave as if they were appended to the command line after all other options. As
a consequence the set of dependent libraries are searched last to resolve
symbols.
2. It is an error if a file cannot be found for a given specifier.
3. Any command line options in effect at the end of the command line parsing apply
to the dependent libraries, e.g. --whole-archive.
4. The linker tries to add a library or relocatable object file from each of the
strings in a .deplibs section by; first, handling the string as if it was
specified on the command line; second, by looking for the string in each of the
library search paths in turn; third, by looking for a lib<string>.a or
lib<string>.so (depending on the current mode of the linker) in each of the
library search paths.
5. A new command line option --no-dependent-libraries tells LLD to ignore the
dependent libraries.
Rationale for the above points:
1. Adding the dependent libraries last makes the process simple to understand
from a developers perspective. All linkers are able to implement this scheme.
2. Error-ing for libraries that are not found seems like better behavior than
failing the link during symbol resolution.
3. It seems useful for the user to be able to apply command line options which
will affect all of the dependent libraries. There is a potential problem of
surprise for developers, who might not realize that these options would apply
to these "invisible" input files; however, despite the potential for surprise,
this is easy for developers to reason about and gives developers the control
that they may require.
4. This algorithm takes into account all of the different ways that ELF linkers
find input files. The different search methods are tried by the linker in most
obvious to least obvious order.
5. I considered adding finer grained control over which dependent libraries were
ignored (e.g. MSVC has /nodefaultlib:<library>); however, I concluded that this
is not necessary: if finer control is required developers can fall back to using
the command line directly.
RFC thread: http://lists.llvm.org/pipermail/llvm-dev/2019-March/131004.html.
Differential Revision: https://reviews.llvm.org/D60274
llvm-svn: 360984
Variables with linkonce_odr and weak_odr linkage shouldn't be internalized
if they're not readonly. Otherwise we may end up with multiple copies of
such variable, so reads and writes will become inconsistent
Differential revision: https://reviews.llvm.org/D61255
llvm-svn: 360577
Summary:
We hit undefined references building with ThinLTO when one source file
contained explicit instantiations of a template method (weak_odr) but
there were also implicit instantiations in another file (linkonce_odr),
and the latter was the prevailing copy. In this case the symbol was
marked hidden when the prevailing linkonce_odr copy was promoted to
weak_odr. It led to unsats when the resulting shared library was linked
with other code that contained a reference (expecting to be resolved due
to the explicit instantiation).
Add a CanAutoHide flag to the GV summary to allow the thin link to
identify when all copies are eligible for auto-hiding (because they were
all originally linkonce_odr global unnamed addr), and only do the
auto-hide in that case.
Most of the changes here are due to plumbing the new flag through the
bitcode and llvm assembly, and resulting test changes. I augmented the
existing auto-hide test to check for this situation.
Reviewers: pcc
Subscribers: mehdi_amini, inglorion, eraman, dexonsmith, arphaman, dang, llvm-commits, steven_wu, wmi
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D59709
llvm-svn: 360466
Gold and ld on Linux already support saving stats, but the
infrastructure is missing on Darwin. Unfortunately it seems like the
configuration from lib/LTO/LTO.cpp is not used.
This patch adds a new LTOStatsFile option and adds plumbing in Clang to
use it on Darwin, similar to the way remarks are handled.
Currnetly the handling of LTO flags seems quite spread out, with a bunch
of duplication. But I am not sure if there is an easy way to improve
that?
Reviewers: anemet, tejohnson, thegameg, steven_wu
Reviewed By: steven_wu
Differential Revision: https://reviews.llvm.org/D60516
llvm-svn: 358753
Summary:
Reapply r357931 with fixes to ThinLTO testcases and llvm-lto tool.
ThinLTOCodeGenerator currently does not preserve llvm.used symbols and
it can internalize them. In order to pass the necessary information to the
legacy ThinLTOCodeGenerator, the input to the code generator is
rewritten to be based on lto::InputFile.
Now ThinLTO using the legacy LTO API will requires data layout in
Module.
"internalize" thinlto action in llvm-lto is updated to run both
"promote" and "internalize" with the same configuration as
ThinLTOCodeGenerator. The old "promote" + "internalize" option does not
produce the same output as ThinLTOCodeGenerator.
This fixes: PR41236
rdar://problem/49293439
Reviewers: tejohnson, pcc, kromanova, dexonsmith
Reviewed By: tejohnson
Subscribers: ormris, bd1976llvm, mehdi_amini, inglorion, eraman, hiraditya, jkorous, dexonsmith, arphaman, dang, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D60421
llvm-svn: 358601
Summary:
ThinLTOCodeGenerator currently does not preserve llvm.used symbols and
it can internalize them. In order to pass the necessary information to the
legacy ThinLTOCodeGenerator, the input to the code generator is
rewritten to be based on lto::InputFile.
This fixes: PR41236
rdar://problem/49293439
Reviewers: tejohnson, pcc, dexonsmith
Reviewed By: tejohnson
Subscribers: mehdi_amini, inglorion, eraman, hiraditya, jkorous, dang, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D60226
llvm-svn: 357931
Currently we have -Rpass for filtering the remarks that are displayed as
diagnostics, but when using -fsave-optimization-record, there is no way
to filter the remarks while generating them.
This adds support for filtering remarks by passes using a regex.
Ex: `clang -fsave-optimization-record -foptimization-record-passes=inline`
will only emit the remarks coming from the pass `inline`.
This adds:
* `-fsave-optimization-record` to the driver
* `-opt-record-passes` to cc1
* `-lto-pass-remarks-filter` to the LTOCodeGenerator
* `--opt-remarks-passes` to lld
* `-pass-remarks-filter` to llc, opt, llvm-lto, llvm-lto2
* `-opt-remarks-passes` to gold-plugin
Differential Revision: https://reviews.llvm.org/D59268
Original llvm-svn: 355964
llvm-svn: 355984
Currently we have -Rpass for filtering the remarks that are displayed as
diagnostics, but when using -fsave-optimization-record, there is no way
to filter the remarks while generating them.
This adds support for filtering remarks by passes using a regex.
Ex: `clang -fsave-optimization-record -foptimization-record-passes=inline`
will only emit the remarks coming from the pass `inline`.
This adds:
* `-fsave-optimization-record` to the driver
* `-opt-record-passes` to cc1
* `-lto-pass-remarks-filter` to the LTOCodeGenerator
* `--opt-remarks-passes` to lld
* `-pass-remarks-filter` to llc, opt, llvm-lto, llvm-lto2
* `-opt-remarks-passes` to gold-plugin
Differential Revision: https://reviews.llvm.org/D59268
llvm-svn: 355964
This allows us to store more info about where we're emitting the remarks
without cluttering LLVMContext. This is needed for future support for
the remark section.
Differential Revision: https://reviews.llvm.org/D58996
Original llvm-svn: 355507
llvm-svn: 355514
Russell Gallop