For `ld64` which uses legacy LTOCodeGenerator, it relies on
writeMergedModule to perform `ld -r` (generates a linked object file).
If all the inputs to `ld -r` is fullLTO bitcode, `ld64` will linked the
bitcode module, internalize all the symbols and write out another
fullLTO bitcode object file. This bitcode file doesn't have all the
bitcode inputs and it should not have LTOPostLink module flag. It will
also cause error when this bitcode object file is linked with other LTO
object file.
Fix the issue by not applying LTOPostLink flag during writeMergedModule
function. The flag should only be added when all the bitcode are linked
and ready to be optimized.
rdar://problem/58462798
Reviewed By: tejohnson
Differential Revision: https://reviews.llvm.org/D84789
There are two ways .llvmbc can be produced:
* clang -c -fembed-bitcode=all (which also produces .llvmcmd)
* LTO backend: ld.lld -mllvm -lto-embed-bitcode or -plugin-opt=-lto-embed-bitcode
.llvmbc and .llvmcmd have the SHF_ALLOC flag, so they can be dropped by
--gc-sections.
This patch sets SectionKind::Metadata to drop the SHF_ALLOC flag. This
is conceptually correct: the two sections are not part of the process
image, so SHF_ALLOC is not appropriate.
`test/LTO/X86/embed-bitcode.ll`: changed `llvm-objcopy -O binary --only-section` to
`llvm-objcopy --dump-section`. `-O binary` does not dump non-SHF_ALLOC sections.
Reviewed By: tejohnson
Differential Revision: https://reviews.llvm.org/D86374
Dead function has its body stripped away, and can cause various
analyses to panic. Also it does not make sense to apply analyses on
such function.
Reviewed By: xazax.hun, MaskRay, wenlei, hoy
Differential Revision: https://reviews.llvm.org/D84715
When sampleFDO is enabled, people may expect they can use
-fno-profile-sample-use to opt-out using sample profile for a certain file.
That could be either for debugging purpose or for performance tuning purpose.
However, when thinlto is enabled, if a function in file A compiled with
-fno-profile-sample-use is imported to another file B compiled with
-fprofile-sample-use, the inlined copy of the function in file B may still
get its profile annotated.
The inconsistency may even introduce profile unused warning because if the
target is not compiled with explicit debug information flag, the function
in file A won't have its debug information enabled (debug information will
be enabled implicitly only when -fprofile-sample-use is used). After it is
imported into file B which is compiled with -fprofile-sample-use, profile
annotation for the outline copy of the function will fail because the
function has no debug information, and that will trigger profile unused
warning.
We add a new attribute use-sample-profile to control whether a function
will use its sample profile no matter for its outline or inline copies.
That will make the behavior of -fno-profile-sample-use consistent.
Differential Revision: https://reviews.llvm.org/D79959
For IR generated by a compiler, this is really simple: you just take the
datalayout from the beginning of the file, and apply it to all the IR
later in the file. For optimization testcases that don't care about the
datalayout, this is also really simple: we just use the default
datalayout.
The complexity here comes from the fact that some LLVM tools allow
overriding the datalayout: some tools have an explicit flag for this,
some tools will infer a datalayout based on the code generation target.
Supporting this properly required plumbing through a bunch of new
machinery: we want to allow overriding the datalayout after the
datalayout is parsed from the file, but before we use any information
from it. Therefore, IR/bitcode parsing now has a callback to allow tools
to compute the datalayout at the appropriate time.
Not sure if I covered all the LLVM tools that want to use the callback.
(clang? lli? Misc IR manipulation tools like llvm-link?). But this is at
least enough for all the LLVM regression tests, and IR without a
datalayout is not something frontends should generate.
This change had some sort of weird effects for certain CodeGen
regression tests: if the datalayout is overridden with a datalayout with
a different program or stack address space, we now parse IR based on the
overridden datalayout, instead of the one written in the file (or the
default one, if none is specified). This broke a few AVR tests, and one
AMDGPU test.
Outside the CodeGen tests I mentioned, the test changes are all just
fixing CHECK lines and moving around datalayout lines in weird places.
Differential Revision: https://reviews.llvm.org/D78403
This method has been commented as deprecated for a while. Remove
it and replace all uses with the equivalent getCalledOperand().
I also made a few cleanups in here. For example, to removes use
of getElementType on a pointer when we could just use getFunctionType
from the call.
Differential Revision: https://reviews.llvm.org/D78882
dso_local leads to direct access even if the definition is not within this compilation unit (it is
still in the same linkage unit). On ELF, such a relocation (e.g. R_X86_64_PC32) referencing a
STB_GLOBAL STV_DEFAULT object can cause a linker error in a -shared link.
If the linkage is changed to available_externally, the dso_local flag should be dropped, so that no
direct access will be generated.
The current behavior is benign, because -fpic does not assume dso_local
(clang/lib/CodeGen/CodeGenModule.cpp:shouldAssumeDSOLocal).
If we do that for -fno-semantic-interposition (D73865), there will be an
R_X86_64_PC32 linker error without this patch.
Reviewed By: tejohnson
Differential Revision: https://reviews.llvm.org/D74751
```
// llvm-objdump -d output (before)
400000: e8 0b 00 00 00 callq 11
400005: e8 0b 00 00 00 callq 11
// llvm-objdump -d output (after)
400000: e8 0b 00 00 00 callq 0x400010
400005: e8 0b 00 00 00 callq 0x400015
// GNU objdump -d. The lack of 0x is not ideal because the result cannot be re-assembled
400000: e8 0b 00 00 00 callq 400010
400005: e8 0b 00 00 00 callq 400015
```
In llvm-objdump, we pass the address of the next MCInst. Ideally we
should just thread the address of the current address, unfortunately we
cannot call X86MCCodeEmitter::encodeInstruction (X86MCCodeEmitter
requires MCInstrInfo and MCContext) to get the length of the MCInst.
MCInstPrinter::printInst has other callers (e.g llvm-mc -filetype=asm, llvm-mca) which set Address to 0.
They leave MCInstPrinter::PrintBranchImmAsAddress as false and this change is a no-op for them.
Reviewed By: jhenderson
Differential Revision: https://reviews.llvm.org/D76580
If we infer the dso_local flag for -fpic, dso_local should be dropped
when we convert a GlobalVariable a declaration. dso_local causes the
generation of direct access (e.g. R_X86_64_PC32). Such relocations referencing
STB_GLOBAL STV_DEFAULT objects are not allowed in a -shared link.
Reviewed By: tejohnson
Differential Revision: https://reviews.llvm.org/D74749
The new behavior matches GNU objdump. A pair of angle brackets makes tests slightly easier.
`.foo:` is not unique and thus cannot be used in a `CHECK-LABEL:` directive.
Without `-LABEL`, the CHECK line can match the `Disassembly of section`
line and causes the next `CHECK-NEXT:` to fail.
```
Disassembly of section .foo:
0000000000001634 .foo:
```
Bdragon: <> has metalinguistic connotation. it just "feels right"
Reviewed By: rupprecht
Differential Revision: https://reviews.llvm.org/D75713
Tools working with object files on Darwin (e.g. lipo) may need to know
properties like the CPU type and subtype of a bitcode file. The logic of
converting a triple to a Mach-O CPU_(SUB_)TYPE should be provided by
LLVM instead of relying on tools to re-implement it.
Differential Revision: https://reviews.llvm.org/D75067
This reverts commit 80a34ae31125aa46dcad47162ba45b152aed968d with fixes.
Previously, since bots turning on EXPENSIVE_CHECKS are essentially turning on
MachineVerifierPass by default on X86 and the fact that
inline-asm-avx-v-constraint-32bit.ll and inline-asm-avx512vl-v-constraint-32bit.ll
are not expected to generate functioning machine code, this would go
down to `report_fatal_error` in MachineVerifierPass. Here passing
`-verify-machineinstrs=0` to make the intent explicit.
This reverts commit 80a34ae31125aa46dcad47162ba45b152aed968d with fixes.
On bots llvm-clang-x86_64-expensive-checks-ubuntu and
llvm-clang-x86_64-expensive-checks-debian only,
llc returns 0 for these two tests unexpectedly. I tweaked the RUN line a little
bit in the hope that LIT is the culprit since this change is not in the
codepath these tests are testing.
llvm\test\CodeGen\X86\inline-asm-avx-v-constraint-32bit.ll
llvm\test\CodeGen\X86\inline-asm-avx512vl-v-constraint-32bit.ll
This reverts commit rGcd5b308b828e, rGcd5b308b828e, rG8cedf0e2994c.
There are issues to be investigated for polly bots and bots turning on
EXPENSIVE_CHECKS.
Summary:
This patch could be treated as a rebase of D33960. It also fixes PR35547.
A fix for `llvm/test/Other/close-stderr.ll` is proposed in D68164. Seems
the consensus is that the test is passing by chance and I'm not
sure how important it is for us. So it is removed like in D33960 for now.
The rest of the test fixes are just adding `--crash` flag to `not` tool.
** The reason it fixes PR35547 is
`exit` does cleanup including calling class destructor whereas `abort`
does not do any cleanup. In multithreading environment such as ThinLTO or JIT,
threads may share states which mostly are ManagedStatic<>. If faulting thread
tearing down a class when another thread is using it, there are chances of
memory corruption. This is bad 1. It will stop error reporting like pretty
stack printer; 2. The memory corruption is distracting and nondeterministic in
terms of error message, and corruption type (depending one the timing, it
could be double free, heap free after use, etc.).
Reviewers: rnk, chandlerc, zturner, sepavloff, MaskRay, espindola
Reviewed By: rnk, MaskRay
Subscribers: wuzish, jholewinski, qcolombet, dschuff, jyknight, emaste, sdardis, nemanjai, jvesely, nhaehnle, sbc100, arichardson, jgravelle-google, aheejin, kbarton, fedor.sergeev, asb, rbar, johnrusso, simoncook, apazos, sabuasal, niosHD, jrtc27, zzheng, edward-jones, atanasyan, rogfer01, MartinMosbeck, brucehoult, the_o, PkmX, jocewei, jsji, lenary, s.egerton, pzheng, cfe-commits, MaskRay, filcab, davide, MatzeB, mehdi_amini, hiraditya, steven_wu, dexonsmith, rupprecht, seiya, llvm-commits
Tags: #llvm, #clang
Differential Revision: https://reviews.llvm.org/D67847
Summary:
This adds support for embedding bitcode in a binary during LTO. The libLTO gains supports the `-lto-embed-bitcode` flag. The option allows users of the LTO library to embed a bitcode section. For example, LLD can pass the option via `ld.lld -mllvm=-lto-embed-bitcode`.
This feature allows doing something comparable to `clang -c -fembed-bitcode`, but on the (LTO) linker level. Having bitcode alongside native code has many use-cases. To give an example, the MacOS linker can create a `-bitcode_bundle` section containing bitcode. Also, having this feature built into LLVM is an alternative to 3rd party tools such as [[ https://github.com/travitch/whole-program-llvm | wllvm ]] or [[ https://github.com/SRI-CSL/gllvm | gllvm ]]. As with these tools, this feature simplifies creating "whole-program" llvm bitcode files, but in contrast to wllvm/gllvm it does not rely on a specific llvm frontend/driver.
Patch by Josef Eisl <josef.eisl@oracle.com>
Reviewers: #llvm, #clang, rsmith, pcc, alexshap, tejohnson
Reviewed By: tejohnson
Subscribers: tejohnson, mehdi_amini, inglorion, hiraditya, aheejin, steven_wu, dexonsmith, dang, cfe-commits, llvm-commits, #llvm, #clang
Tags: #clang, #llvm
Differential Revision: https://reviews.llvm.org/D68213
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:
During IR Linking, if the types of two globals in destination and source
modules are the same, it can only be because the global in the
destination module is originally from the source module and got added to
the destination module from a shared metadata.
We shouldn't map this type to itself in case the type's components get
remapped to a new type from the destination (for instance, during the
loop over SrcM->getIdentifiedStructTypes() further below in
IRLinker::computeTypeMapping()).
Fixes PR40312.
Reviewers: tejohnson, pcc, srhines
Subscribers: mehdi_amini, hiraditya, steven_wu, dexonsmith, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D66814
llvm-svn: 371643
Test added in r369766 had the wrong target arch for the X86 directory,
leading to some bot failures. Fix it to have the appropriate target.
llvm-svn: 369774
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
GNU as keeps the original symbol in the symbol table for defined @ and
@@, but suppresses it in other cases (@@@ or undefined). The original
symbol is usually undesired:
In a shared object, the original symbol can be localized with a version
script, but it is hard to remove/localize in an archive:
1) a post-processing step removes the undesired original symbol
2) consumers (executable) of the archive are built with the
version script
Moreover, it can cause linker issues like binutils PR/18703 if the
original symbol name and the base name of the versioned symbol is the
same (both ld.bfd and gold have some code to work around defined @ and
@@). In lld, if it sees f and f@v1:
--version-script =(printf 'v1 {};') => f and f@v1
--version-script =(printf 'v1 { f; };') => f@v1 and f@@v1
It can be argued that @@@ added on 2000-11-13 corrected the @ and @@ mistake.
This patch catches some more multiple version errors (defined @ and @@),
and consistently suppress the original symbol. This addresses all the
problems listed above.
If the user wants other aliases to the versioned symbol, they can copy
the original symbol to other symbol names with .set directive, e.g.
.symver f, f@v1 # emit f@v1 but not f into .symtab
.set f_impl, f # emit f_impl into .symtab
llvm-svn: 369233
GlobalAlias and GlobalIFunc ought to be treated the same by the IR
linker, so we can generalize the code to be in terms of their common
base class GlobalIndirectSymbol.
Differential Revision: https://reviews.llvm.org/D55046
llvm-svn: 368357
For consistency with normal instructions and clarity when reading IR,
it's best to print the %0, %1, ... names of function arguments in
definitions.
Also modifies the parser to accept IR in that form for obvious reasons.
llvm-svn: 367755
We are about to add enum attributes with AttrKind numbers >= 63. This
means we cannot use AttrKind #63 to test for an invalid attribute number
in the RAW format anymore. This patch changes the number of an invalid
attribute to #255. There is no change to the character of the tests.
Differential Revision: https://reviews.llvm.org/D64531
llvm-svn: 365722
This reverts r364422 (git commit 1a3dc761860d620ac8ed7e32a4285952142f780b)
The inlining cost calculation is incorrect, leading to stack overflow due to large stack frames from heavy inlining.
llvm-svn: 365000
Summary:
Doing better separation of Cost and Threshold.
Cost counts the abstract complexity of live instructions, while Threshold is an upper bound of complexity that inlining is comfortable to pay.
There are two parts:
- huge 15K last-call-to-static bonus is no longer subtracted from Cost
but rather is now added to Threshold.
That makes much more sense, as the cost of inlining (Cost) is not changed by the fact
that internal function is called once. It only changes the likelyhood of this inlining
being profitable (Threshold).
- bonus for calls proved-to-be-inlinable into callee is no longer subtracted from Cost
but added to Threshold instead.
While calculations are somewhat different, overall InlineResult should stay the same since Cost >= Threshold compares the same.
Reviewers: eraman, greened, chandlerc, yrouban, apilipenko
Reviewed By: apilipenko
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D60740
llvm-svn: 364422
Dependent libraries support for the legacy api was committed in a
broken state (see: https://reviews.llvm.org/D60274). This was missed
due to the painful nature of having to integrate the changes into a
linker in order to test. This change implements support for dependent
libraries in the legacy LTO api:
- I have removed the current api function, which returns a single
string, and added functions to access each dependent library
specifier individually.
- To reduce the testing pain, I have made the api functions as thin as
possible to maximize coverage from llvm-lto.
- When doing ThinLTO the system linker will load the modules lazily
when scanning the input files. Unfortunately, when modules are
lazily loaded there is no access to module level named metadata. To
fix this I have added api functions that allow querying the IRSymtab
for the dependent libraries. I hope to expand the api in the future
so that, eventually, all the information needed by a client linker
during scan can be retrieved from the IRSymtab.
Differential Revision: https://reviews.llvm.org/D62935
llvm-svn: 363140
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
-t is --symbols in llvm-readobj but --section-details (unimplemented) in readelf.
The confusing option should not be used since we aim for improving
compatibility.
Keep just one llvm-readobj -t use case in test/tools/llvm-readobj/symbols.test
llvm-svn: 359661
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
Summary:
When linking two llvm.used arrays, if the resulting merged
array ends up with duplicated elements (with the same name) but with
different types, the IRLinker was crashing. This was supposed to be
legal, as the IRLinker bitcasts elements to match types in these
situations.
This bug was exposed by D56928 in clang to support attribute used
in member functions of class templates. Crash happened when self-hosting
with LTO. Since LLVM depends on attribute used to generate code
for the dump() method, ubiquitous in the code base, many input bc
had a definition of this method referenced in their llvm.used array.
Some of these classes got optimized, changing the type of the first
parameter (this) in the dump method, leading to a scenario with a
pool of valid definitions but some with a different type, triggering
this bug.
This is a memory bug: ValueMapper depends on (calls) the materializer
provided by IRLinker, and this materializer was freely calling RAUW
methods whenever a global definition was updated in the temporary merged
output file. However, replaceAllUsesWith may or may not destroy
constants that use this global. If the linked definition has a type
mismatch regarding the new def and the old def, the materializer would
bitcast the old type to the new type and the elements of the llvm.used
array, which already uses bitcast to i8*, would end up with elements
cascading two bitcasts. RAUW would then indirectly call the
constantfolder to update the constant to the new ref, which would,
instead of updating the constant, destroy it to be able to create
a new constant that folds the two bitcasts into one. The problem is that
ValueMapper works with pointers to the same constants that may be
getting destroyed by RAUW. Obviously, RAUW can update references in the
Module to do not use the old destroyed constant, but it can't update
ValueMapper's internal pointers to these constants, which are now
invalid.
The approach here is to move the task of RAUWing old definitions
outside of the materializer.
Test Plan:
Added LIT test case, tested clang self-hosting with D56928 and
verified it works
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D59552
llvm-svn: 356597
