llvm-dev message: https://lists.llvm.org/pipermail/llvm-dev/2021-May/150465.html
In an ELF shared object, a default visibility defined symbol is preemptible by default.
This creates some missed optimization opportunities. -fno-semantic-interposition can optimize -fPIC:
* in Clang: avoid GOT/PLT cost for variable access/function calls to external linkage definition in the same TU
* in GCC: enable interprocedural optimizations (including inlining) and avoid PLT
See https://gist.github.com/MaskRay/2d4dfcfc897341163f734afb59f689c6 for more information.
-Bsymbolic-functions is more aggressive than -fvisibility-inlines-hidden (present since 2012) as it applies
to all function definitions. It can
* avoid PLT for cross-TU function calls && reduce dynamic symbol lookup
* reduce dynamic symbol lookup for taking function addresses and optimize out GOT/TOC on x86-64/ppc64
With both options, the libLLVM.so and libclang-cpp.so performance should
be closer to PIE binary linking against `libLLVM*.a` and `libclang*.a`
(In a -DLLVM_TARGETS_TO_BUILD=X86 build, the number of JUMP_SLOT decreases from 12716 to 1628, and the number of GLOB_DAT decreases from 1918 to 1313
The built clang with `-DLLVM_LINK_LLVM_DYLIB=on -DCLANG_LINK_CLANG_DYLIB=on` is significantly faster.
See the Linux kernel build result https://bugs.archlinux.org/task/70697
)
Some implication:
Interposing a subset of functions is no longer supported.
(This is fragile anyway and cannot really be supported. For Mach-O we don't use
`ld -interpose`, so interposition is not supported on Mach-O at all.)
Compiling a program which takes the address of any LLVM function with
`{gcc,clang} -fno-pic` and expects the address to equal to the address taken
from libLLVM.so or libclang-cpp.so is unsupported. I am fairly confident that
llvm-project shouldn't have different behaviors depending on such pointer
equality (as we've been using -fvisibility-inlines-hidden which applies to
inline functions for a long time), but if we accidentally do, users should be
aware that they should not make assumption on pointer equality in `-fno-pic`
mode.
Reviewed By: phosek
Differential Revision: https://reviews.llvm.org/D102090
`__mh_(execute|dylib|dylinker|bundle|preload|object)_header` are special symbols whose values hold the VMA of the Mach header to support introspection. They are attached to the first section in `__TEXT`, even though their addresses are outside `__TEXT`, and they do not refer to code.
It is normally harmless, but when the first section of `__TEXT` has no other symbols, `__mh_*_header` is considered by the disassembler when determing function boundaries. Since `__mh_*_header` refers to an address outside `__TEXT`, the boundary determination fails and disassembly quits.
Since `__TEXT,__text` normally has symbols, this bug is obscured. Experiments placing `__stubs` and `__stub_helper` first exposed the bug, since neither has symbols.
Differential Revision: https://reviews.llvm.org/D101786
The readelf command guide shows the short options used as aliases but
these are not found in the help text unless --show-hidden is used, other
tools show aliases with --help. This change fixes the help output to be
consistent with the command guide.
Differential Revision: https://reviews.llvm.org/D102173
In the help output of other tools and in the symbolizer command guide,
Mach-O specific options are in their own section. This change fixes the
symbolizer help output to be consistent.
Differential Revision: https://reviews.llvm.org/D102178
When making compilation relocatable, for example in distributed
compilation scenarios, we want to set compilation dir to a relative
value like `.` but this presents a problem when generating reports
because if the file path is relative as well, for example `..`, you
may end up writing files outside of the output directory.
This change introduces a flag that allows overriding the compilation
directory that's stored inside the profile with a different value that
is absolute.
Differential Revision: https://reviews.llvm.org/D100232
Originally landed in: 6400905a61
Reverted in: 668dccc396
Fix branch coverage merging in FunctionCoverageSummary::get() for instantiation
groups.
This change corrects the implementation for the branch coverage summary to do
the same thing for branches that is done for lines and regions. That is,
across function instantiations in an instantiation group, the maximum branch
coverage found in any of those instantiations is returned, with the total
number of branches being the same across instantiations.
Differential Revision: https://reviews.llvm.org/D102193
groups.
This change corrects the implementation for the branch coverage
summary to do the same thing for branches that is done for lines and regions.
That is, across function instantiations in an instantiation group, the maximum
branch coverage found in any of those instantiations is returned, with the
total number of branches being the same across instantiations.
Differential Revision: https://reviews.llvm.org/D102193
This patch adds JSON output style to llvm-symbolizer to better support CLI automation by providing a machine readable output.
Reviewed By: jhenderson
Differential Revision: https://reviews.llvm.org/D96883
There are cases where a concrete DIE with DW_TAG_subprogram can have
abstract_origin attribute, so we handle that situation as well.
Differential Revision: https://reviews.llvm.org/D101025
This change was originally landed in: 5000a1b4b9
It was reverted in: 061e071d8c
This change adds support for a new WASM_SEG_FLAG_STRINGS flag in
the object format which works in a similar fashion to SHF_STRINGS
in the ELF world.
Unlike the ELF linker this support is currently limited:
- No support for SHF_MERGE (non-string merging)
- Always do full tail merging ("lo" can be merged with "hello")
- Only support single byte strings (p2align 0)
Like the ELF linker merging is only performed at `-O1` and above.
This fixes part of https://bugs.llvm.org/show_bug.cgi?id=48828,
although crucially it doesn't not currently support debug sections
because they are not represented by data segments (they are custom
sections)
Differential Revision: https://reviews.llvm.org/D97657
This change adds support for a new WASM_SEG_FLAG_STRINGS flag in
the object format which works in a similar fashion to SHF_STRINGS
in the ELF world.
Unlike the ELF linker this support is currently limited:
- No support for SHF_MERGE (non-string merging)
- Always do full tail merging ("lo" can be merged with "hello")
- Only support single byte strings (p2align 0)
Like the ELF linker merging is only performed at `-O1` and above.
This fixes part of https://bugs.llvm.org/show_bug.cgi?id=48828,
although crucially it doesn't not currently support debug sections
because they are not represented by data segments (they are custom
sections)
Differential Revision: https://reviews.llvm.org/D97657
The nm command guide shows the short options used as aliases but these
are not found in the help text unless --show-hidden is used, other tools
show aliases with --help. This change fixes the help output to be
consistent with the command guide.
Differential Revision: https://reviews.llvm.org/D102072
This is preparation for the https://reviews.llvm.org/D101025.
The D101025 will start calculating var locstats for concrete fns
that refere to an abstract origin as well.
Printing pass manager invocations is fairly verbose and not super
useful.
This allows us to remove DebugLogging from pass managers and PassBuilder
since all logging (aside from analysis managers) goes through
instrumentation now.
This has the downside of never being able to print the top level pass
manager via instrumentation, but that seems like a minor downside.
Reviewed By: ychen
Differential Revision: https://reviews.llvm.org/D101797
We're trying to move DebugLogging into instrumentation, rather than
being part of PassManagers/AnalysisManagers.
Reviewed By: ychen
Differential Revision: https://reviews.llvm.org/D102093
The dwarfdump command guide shows the short options used as aliases but
these are not found in the help text unless --show-hidden is used.
Investigating other tools some follow this pattern, others like
llvm-objdump show aliases with --help. This change fixes the help output
to be consistent with the command guide. This includes updating alias
descriptions in the help output to use "--".
As part of this change I updated cmdline.test, including some options
that were missing testing.
Differential Revision: https://reviews.llvm.org/D101646
Fix up my recent commit rG1128311a19179ceca799ff0fbc4dd206ab56e560 to
use std::make_unique instead of std::unique_ptr(new), as requested by
David Blaikie.
Differential Revision: https://reviews.llvm.org/D101822
PR50160: we currently ignore non-PT_PHDR segments with no sections, not
accounting for its p_offset and p_filesz: this can cause an out-of-bounds write
in `writeSegmentData` if the p_offset+p_filesz is larger than the total file
size.
This can be fixed by setting p_offset=p_filesz=0. The logic nicely unifies with
the logic added in D90897.
Reviewed By: jhenderson, rupprecht
Differential Revision: https://reviews.llvm.org/D101560
This untangles the MCContext and the MCObjectFileInfo. There is a circular
dependency between MCContext and MCObjectFileInfo. Currently this dependency
also exists during construction: You can't contruct a MOFI without a MCContext
without constructing the MCContext with a dummy version of that MOFI first.
This removes this dependency during construction. In a perfect world,
MCObjectFileInfo wouldn't depend on MCContext at all, but only be stored in the
MCContext, like other MC information. This is future work.
This also shifts/adds more information to the MCContext making it more
available to the different targets. Namely:
- TargetTriple
- ObjectFileType
- SubtargetInfo
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D101462
The internal `cl::opt` option --x86-asm-syntax sets the AsmParser and AsmWriter
dialect. The option is used by llc and llvm-mc tests to set the AsmWriter dialect.
This patch adds -M {att,intel} as GNU objdump compatible aliases (PR43413).
Note: the dialect is initialized when the MCAsmInfo is constructed.
`MCInstPrinter::applyTargetSpecificCLOption` is called too late and its MCAsmInfo
reference is const, so changing the `cl::opt` in
`MCInstPrinter::applyTargetSpecificCLOption` is not an option, at least without
large amount of refactoring.
Reviewed By: hoy, jhenderson, thakis
Differential Revision: https://reviews.llvm.org/D101695
Fix PR45416: the diagnostic when '=' is missing is misleading.
`FileOutputBuffer::create` returns successfully when the filename is empty
(the temporary file is `.tmp%%%%%%%`), but `FileOutputBuffer::commit` will error when
renaming `.tmp%%%%%%%` to the empty name).
Reviewed By: jhenderson
Differential Revision: https://reviews.llvm.org/D101697
Unwind info generated by MSVC tends to have relocations pointing at
static "label" symbols like "$LN4" instead of regular ones based on
the actual function's name. Try to resolve such symbols to a non-label
symbol if possible (ideally to an external symbol), to improve
the readability.
Differential Revision: https://reviews.llvm.org/D101567
When dumping multiple pieces of information (e.g. --all-headers),
there is sometimes no separator between two pieces.
This patch uses the "\nheader:\n" style, which generally improves
compatibility with GNU objdump.
Note: objdump -t/-T does not add a newline before "SYMBOL TABLE:" and "DYNAMIC SYMBOL TABLE:".
We add a newline to be consistent with other information.
`objdump -d` prints two empty lines before the first 'Disassembly of section'.
We print just one with this patch.
Differential Revision: https://reviews.llvm.org/D101796
Reapply 7368624 after revert and fix
Looking at other tools using tablegen for help output, general options
like --help are not separated from other options. This change removes
the "Generic Options" option group so the options are listed together.
the macho specific option group is left unaffected.
The test help.test was modified to reflect this change.
Differential Revision: https://reviews.llvm.org/D101652
Looking at other tools using tablegen for help output, general options
like --help are not separated from other options. This change removes
the "Generic Options" option group so the options are listed together.
the macho specific option group is left unaffected.
The test help.test was modified to reflect this change.
Differential Revision: https://reviews.llvm.org/D101652
This reverts the revert 02c5ba8679
Fix:
Pass was registered as DUMMY_FUNCTION_PASS causing the newpm-pass
functions to be doubly defined. Triggered in -DLLVM_ENABLE_MODULE=1
builds.
Original commit:
This patch implements expansion of llvm.vp.* intrinsics
(https://llvm.org/docs/LangRef.html#vector-predication-intrinsics).
VP expansion is required for targets that do not implement VP code
generation. Since expansion is controllable with TTI, targets can switch
on the VP intrinsics they do support in their backend offering a smooth
transition strategy for VP code generation (VE, RISC-V V, ARM SVE,
AVX512, ..).
Reviewed By: rogfer01
Differential Revision: https://reviews.llvm.org/D78203
Add a demangling support for a small subset of a new Rust mangling
scheme, with complete support planned as a follow up work.
Intergate Rust demangling into llvm-cxxfilt and use llvm-cxxfilt for
end-to-end testing. The new Rust mangling scheme uses "_R" as a prefix,
which makes it easy to disambiguate it from other mangling schemes.
The public API is modeled after __cxa_demangle / llvm::itaniumDemangle,
since potential candidates for further integration use those.
Reviewed By: dblaikie
Differential Revision: https://reviews.llvm.org/D101444
The right symbol flag mask is ~0x7, not ~0xf.
Also emit string names for the other flags (we were missing some).
Reviewed By: #lld-macho, gkm
Differential Revision: https://reviews.llvm.org/D101548
This introduces a flag that aborts if we ever reduce to IR that fails
the verifier.
Reviewed By: swamulism, arichardson
Differential Revision: https://reviews.llvm.org/D101279
Oliver Stannard