[ELF] Move whyExtract/backwardReferences from LinkerDriver to Ctx. NFC

Ctx was recently added as a more suitable place for such singletons.

[ELF] Move SymbolUnion assertions to source file

Otherwise they fires for every single file which includes the header,
which is very noisy when building.

Reviewed By: MaskRay, peter.smith

Differen

[ELF] Move SymbolUnion assertions to source file

Otherwise they fires for every single file which includes the header,
which is very noisy when building.

Reviewed By: MaskRay, peter.smith

Differential Revision: https://reviews.llvm.org/D124041

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[ELF] Move section assignment from initializeSymbols to postParse

https://discourse.llvm.org/t/parallel-input-file-parsing/60164

initializeSymbols currently sets Defined::section and handles non-pr

[ELF] Move section assignment from initializeSymbols to postParse

https://discourse.llvm.org/t/parallel-input-file-parsing/60164

initializeSymbols currently sets Defined::section and handles non-prevailing
COMDAT groups. Move the code to the parallel postParse to reduce work from the
single-threading code path and make parallel section initialization infeasible.

Postpone reporting duplicate symbol errors so that the messages have the
section information. (`Defined::section` is assigned in postParse and another
thread may not have the information).

* duplicated-synthetic-sym.s: BinaryFile duplicate definition (very rare) now
has no section information
* comdat-binding: `%t/w.o %t/g.o` leads to an undesired undefined symbol. This
is not ideal but we report a diagnostic to inform that this is unsupported.
(See release note)
* comdat-discarded-lazy.s: %tdef.o is unextracted. The new behavior (discarded
section error) makes more sense
* i386-comdat.s: switched to a better approach working around
.gnu.linkonce.t.__x86.get_pc_thunk.bx in glibc<2.32 for x86-32.
Drop the ancient no-longer-relevant workaround for __i686.get_pc_thunk.bx

Depends on D120640

Differential Revision: https://reviews.llvm.org/D120626

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Revert D120626 "[ELF] Move section assignment from initializeSymbols to postParse"

This reverts commit c30e6447c0225f675773d07f2b6d4e3c2b962155.
It exposed brittle support for __x86.get_pc_thunk.bx.

Revert D120626 "[ELF] Move section assignment from initializeSymbols to postParse"

This reverts commit c30e6447c0225f675773d07f2b6d4e3c2b962155.
It exposed brittle support for __x86.get_pc_thunk.bx.
Need to think a bit how to support __x86.get_pc_thunk.bx.

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[ELF] Suppress duplicate symbol error for __x86.get_pc_thunk.bx

[ELF] Move section assignment from initializeSymbols to postParse

https://discourse.llvm.org/t/parallel-input-file-parsing/60164

initializeSymbols currently sets Defined::section and handles non-pr

[ELF] Move section assignment from initializeSymbols to postParse

https://discourse.llvm.org/t/parallel-input-file-parsing/60164

initializeSymbols currently sets Defined::section and handles non-prevailing
COMDAT groups. Move the code to the parallel postParse to reduce work from the
single-threading code path and make parallel section initialization infeasible.

Postpone reporting duplicate symbol errors so that the messages have the
section information. (`Defined::section` is assigned in postParse and another
thread may not have the information).

* duplicated-synthetic-sym.s: BinaryFile duplicate definition (very rare) now
has no section information
* comdat-binding: `%t/w.o %t/g.o` leads to an undesired undefined symbol. This
is not ideal but we report a diagnostic to inform that this is unsupported.
(See release note)
* comdat-discarded-lazy.s: %tdef.o is unextracted. The new behavior (discarded
section error) makes more sense

Depends on D120640

Reviewed By: peter.smith

Differential Revision: https://reviews.llvm.org/D120626

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[ELF] Set the priority of STB_GNU_UNIQUE the same as STB_WEAK

In GCC -fgnu-unique output, STB_GNU_UNIQUE symbols are always defined relative
to a section in a COMDAT group. Currently `other` cannot

[ELF] Set the priority of STB_GNU_UNIQUE the same as STB_WEAK

In GCC -fgnu-unique output, STB_GNU_UNIQUE symbols are always defined relative
to a section in a COMDAT group. Currently `other` cannot be STB_GNU_UNIQUE for
valid input, so this patch is NFC.

If we switch to the model that ignores COMDAT resolution when performing symbol
resolution (D120626), this will fix bogus `relocation refers to a symbol in a
discarded section` errors when mixing -fno-gnu-unique objects with -fgnu-unique
objects.

Differential Revision: https://reviews.llvm.org/D120640

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[ELF] Rename Symbol::compare to shouldReplace. NFC

The return value is not a boolean instead of a tri-state.
Suggested by Peter Smith in D120640.

[ELF] Change global variable backwardReferences to a LinkerDriver member variable. NFC

Similar to whyExtract.

[ELF] Move --print-archive-stats= and --why-extract= beside --warn-backrefs report

So that early errors don't suppress their output.

[ELF] Update comment. NFC

[ELF] Simplify resolveDefined and resolveCommon

This is NFC for valid input (COMMON symbols cannot be weak or versioned).

[ELF] Simplify --fortran-common. NFC

[ELF] De-template Symbol::resolveLazy. NFC

[ELF] Move isUsedInRegularObj assignment from ctor to call sites. NFC

This removes the tricky
`isUsedInRegularObj(!file || file->kind() == InputFile::ObjKind)`
and the copy from `Symbol::mergeProper

[ELF] Move isUsedInRegularObj assignment from ctor to call sites. NFC

This removes the tricky
`isUsedInRegularObj(!file || file->kind() == InputFile::ObjKind)`
and the copy from `Symbol::mergeProperties`.

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[ELF] Move duplicate symbol check after input file parsing

https://discourse.llvm.org/t/parallel-input-file-parsing/60164

To decouple symbol initialization and section initialization, `Defined::sec

[ELF] Move duplicate symbol check after input file parsing

https://discourse.llvm.org/t/parallel-input-file-parsing/60164

To decouple symbol initialization and section initialization, `Defined::section`
assignment should be postponed after input file parsing. To avoid spurious
duplicate definition error due to two definitions in COMDAT groups of the same
signature, we should postpone the duplicate symbol check.

The function is called postScan instead of a more specific name like
checkDuplicateSymbols, because we may merge Symbol::mergeProperties into
postScan. It is placed after compileBitcodeFiles to apply to ET_REL files
produced by LTO. This causes minor diagnostic regression
for skipLinkedOutput configurations: ld.lld --thinlto-index-only a.bc b.o
(bitcode definition prevails) won't detect duplicate symbol error. I think this
is an acceptable compromise. The important cases where (a) both files are
bitcode or (b) --thinlto-index-only is unused are still detected.

Reviewed By: ikudrin

Differential Revision: https://reviews.llvm.org/D119908

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[ELF] reportDuplicate: change Symbol * to const Symbol &. NFC

[ELF] Parse archives as --start-lib object files

https://maskray.me/blog/2022-01-16-archives-and-start-lib

For every definition in an extracted archive member, we intern the symbol twice,
once for

[ELF] Parse archives as --start-lib object files

https://maskray.me/blog/2022-01-16-archives-and-start-lib

For every definition in an extracted archive member, we intern the symbol twice,
once for the archive index entry, once for the .o symbol table after extraction.
This is inefficient.

Symbols in a --start-lib ObjFile/BitcodeFile are only interned once because the
result is cached in symbols[i].

Just handle an archive using the --start-lib code path. We can therefore remove
ArchiveFile and LazyArchive. For many projects, archive member extraction ratio
is high and it is a net performance win. Linking a Release build of clang is
1.01x as fast.

Note: --start-lib scans symbols in the same order that llvm-ar adds them to the
index, so in the common case the semantics should be identical. If the archive
symbol table was created in a different order, or is incomplete, this strategy
may have different semantics. Such cases are considered user error.

The `is neither ET_REL nor LLVM bitcode` error is changed to a warning.
Previously an archive may have such members without a diagnostic. Using a
warning prevents breakage.

* For some tests, the diagnostics get improved where we did not consider
the archive member name: `b.a:` => `b.a(b.o):`.
* `no-obj.s`: the link is now allowed, matching GNU ld
* `archive-no-index.s`: the `is neither ET_REL nor LLVM bitcode` diagnostic is
demoted to a warning.
* `incompatible.s`: even when an archive is unextracted, we may report an
"incompatible with" error.

---

I recently decreased sizeof(SymbolUnion) by 8 and decreased memory usage quite a
bit, so retaining `symbols` for un-extracted archive members should not cause a
memory usage problem.

Reviewed By: peter.smith

Differential Revision: https://reviews.llvm.org/D119074

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[ELF] Clean up headers. NFC

[ELF] Symbol::replace: use the old nameData/nameSize. NFC

Currently `this->getName() == newSym.getName()`.
By keeping the old nameData/nameSize, newSym's nameData/nameSize will be
ignored. The call

[ELF] Symbol::replace: use the old nameData/nameSize. NFC

Currently `this->getName() == newSym.getName()`.
By keeping the old nameData/nameSize, newSym's nameData/nameSize will be
ignored. The call sites can avoid calling getName().

printTraceSymbol needs to take the symbol name since `other`'s name is empty.

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[ELF] Remove !isLazy() condition from computeBinding

Seems applicable since we demote lazy symbols to Undefined (D111365).

[ELF] Remove config->relocatable condition from Symbol::computeBinding

[ELF] Speed up Symbol::computeBinding. NFC

When computeBinding is inlined into includeInDynsym and computeIsPreemptible,
the optimizer can remove the config->gnuUnique load.

[ELF] Slightly speed up Symbol::includeInDynsym. NFC

[ELF] Simplify Symbol::includeInDynsym