Dynamic relocations are expensive on ELF/Linux platforms because they
are applied in userspace on process startup. Therefore, it is worth
optimizing them to make PIE and PIC dylib builds faster. In +asserts
builds (non-NDEBUG), nikic identified these schedule class name string
pointers as the leading source of dynamic relocations. [1]
This change uses llvm::StringTable and the StringToOffsetTable TableGen
helper to turn the string pointers into 32-bit offsets into a separate
character array.
The number of dynamic relocations is reduced by ~60%:
❯ llvm-readelf --dyn-relocations lib/libLLVM.so | wc -l
381376 # before
155156 # after
The test suite time is modestly affected, but I'm running on a shared
noisy workstation VM with a ton of cores:
https://gist.github.com/rnk/f38882c2fe2e63d0eb58b8fffeab69de
Testing Time: 100.88s # before
Testing Time: 78.50s. # after
Testing Time: 96.25s. # before again
I haven't used any fancy hyperfine/denoising tools, but I think the
result is clearly visible and we should ship it.
[1] https://gist.github.com/nikic/554f0a544ca15d5219788f1030f78c5a
This fixes a TODO and avoids a special case. Also required
hacking up a few cases to avoid asserting in codegen; it's not
confidence inspiring that there is only one codegen test using
a bridgeos triple and its specifically for the exp10 libcall
names.
This also changes the behavior, losing an extra leading _ in the
emitted name matching the other apple outputs. I have no idea if
this is right or not. IMO it's someone from apple's problem to fix
it and add appropriate test coverage, or we can rip all references
to BridgeOS out from upstream.
As pointed in #145438, the order of elements in `v2::DescriptorRange` is
wrong according to the root signature file format. This changes the
order and updates the code and test to continue to pass.
Closes: #145438
---------
Co-authored-by: joaosaffran <joao.saffran@microsoft.com>
* Fix the crash for `.equiv b, undef; b:` (.equiv equates a symbol to an expression and reports an error if the symbol was already defined).
* Remove redundant isVariable check from emitFunctionEntryLabel
Pull Request: https://github.com/llvm/llvm-project/pull/145460
String table size is too big for large binary when symbol table is
enabled. Some strings in strtab is same so it can be reused.
This patch revives 9ffeaaa authored by mstorsjo with the prioritized
string table builder to fix debug section name issue (see 4d2eda2
for more details).
---------
Co-authored-by: Wen Haohai <whh108@live.com>
Co-authored-by: James Henderson <James.Henderson@sony.com>
This dump feature does not pass MCAsmInfo to the printer function.
When we remove MCSpecifierExpr subclasses (and the printImpl overrides),
we will not be able to print target-specific specifier strings.
Just print a textual representation.
Expressions with specifier can only be folded during relocation
generatin. At parse time the `MCAssembler *` argument might be null, and
targets should not rely on the evaluateAsRelocatable result.
Therefore, we can move evaluateAsRelocatableImpl from MCSpecifierExpr to
MCAsmInfo, so that targets do not need to inherit from MCSpecifierExpr.
* Make relocation specifier code closer (MCAsmInfo defines specifiers).
* MCExpr::print has an optional MCAsmInfo argument, which is
error-prone when omitted.
* Enable MCSpecifierExpr
Introduce MCAsmInfo::UsesSetToEquateSymbol to control the preferred
syntax for symbol equating. We now favor the more readable and common
`symbol = expression` syntax over `.set`. This aligns with pre- https://reviews.llvm.org/D44256 behavior.
On Apple platforms, this resolves a clang -S vs -c behavior difference (resolves#104623).
For targets whose = support is unconfirmed, UsesSetToEquateSymbol is set to false.
This also minimizes test updates.
Pull Request: https://github.com/llvm/llvm-project/pull/142289
This function was a workaround used to detect cyclic dependency
(properly resolved by 343428c666f9293ae260bbcf79130562b830b268).
We do not want backends to use it. However, #112251 exposed it to MCExpr
to be reused by AMDGPU. Keep the workaround within AMDGPU to prevent
other backends from accidentally relying on it.
Many targets define MCTargetExpr subclasses just to encode an expression
with a relocation specifier. Create a generic MCSpecifierExpr to be
inherited instead. Migrate M68k and SPARC as examples.
- try_emplace(Key) is shorter than insert(std::make_pair(Key, 0)).
- try_emplace performs value initialization without value parameters.
- We overwrite values on successful insertion anyway.
This patch addresses an issue where an anonymous DWARF line table symbol
could be inadvertently defined multiple times, leading to an "symbol ''
is already defined" error during assembly or object file emission. This
issue happens for empty functions when
`-emit-func-debug-line-table-offsets` is enabled.
The root cause is the creation of the "end sequence" entry for a DWARF
line table. This entry was sometimes created by copying the last
existing line table entry. If this last entry was a special one (created
for the purpose of marking the position in the line table stream and
having an anonymous symbol attached), the copied end-sequence entry
would also incorrectly reference this same anonymous symbol.
Consequently, when the line table was finally emitted, the DWARF
emission logic would attempt to emit a label for this anonymous symbol
twice, triggering the redefinition error.
The fix ensures that when an end-sequence line table entry is created,
it does not inherit any special stream label from the entry it might
have been based on, thereby preventing the duplicate label emission.
This builds on top of commit 9d0754ada5dbbc0c009bcc2f7824488419cc5530
("[MC] Relax fragments eagerly") and relaxes fragments eagerly to
eliminate MCSection::HasLayout and `getFragmentOffset` overhead.
Relands 1a47f3f3db66589c11f8ddacfeaecc03fb80c510
Builds with many text sections (e.g. full LTO) shall observe a decrease
in compile time.
---
In addition, ensure `.fill` and `.space` directives with expressions are
re-evaluated during fragment relaxation, as their sizes may change.
Continue iteration to prevent stale, incorrect sizes.
This change has to be coupled with the fragment algorithm change
as otherwise the test test/MC/ELF/layout-interdependency.s would not
converge.
Fixes#123402 and resolves the root cause of #100283, building on error
postponing from commit 38b12d4a7c219b46d1cb52580cbacbdb931262f2.
For AArch64/label-arithmetic-diags-elf.s, the extra iteration
reports a .fill error early and suppresses the fixup/relocation errors.
Just split the tests.
When MCContext is used for the second compile of
llvm/test/MC/ELF/twice.ll, ensure that .rel.text and .rel.eh_frame
strings do not come from the previous compilation copies.
Sym.isInSection() calls findAssociatedFragment, which traverses the
expression tree. This can be replaced by calling evaluateAsRelocatableImpl
first and then inspecting the MCValue result.
The dummy fragment is primarily used by MCAsmStreamer::emitLabel to
track the defined state. We can replace it with an arbitrary fragment.
Remove MCDummyFragment introduced for https://github.com/llvm/llvm-project/issues/24860
Commit bb03cdcb441fd68da9d1ebb7d5f39f73667cd39c caused a Linux kernel
regression https://github.com/ClangBuiltLinux/linux/issues/2091
When a section contains linker-relaxable MCAlignmentFragment but no
linker-relaxable instructions, the RISCVAsmBackend::isPCRelFixupResolved
code path should be taken as well. The #76552 condition in the fragment
walk code will make the fixup unresolvable, leading to a relocation.
As requested in a previous PR, this change moves all structs related to
RTS0 to RTS0 namespace.
---------
Co-authored-by: joaosaffran <joao.saffran@microsoft.com>
GNU Assembler supports symbol reassignment via .set, .equ, or =.
However, LLVM's integrated assembler only allows reassignment for
MCConstantExpr cases, as it struggles with scenarios like:
```
.data
.set x, 0
.long x // reference the first instance
x = .-.data
.long x // reference the second instance
.set x,.-.data
.long x // reference the third instance
```
Between two assignments binds, we cannot ensure that a reference binds
to the earlier assignment. We use MCSymbol::IsUsed and other conditions
to reject potentially unsafe reassignments, but certain MCConstantExpr
uses could be unsafe as well.
This patch enables reassignment by cloning the symbol upon reassignment
and updating the symbol table. Existing references to the original
symbol remain unchanged, and the original symbol is excluded from the
emitted symbol table.
The conditions in parseAssignmentExpression are conservative. We should
also report an error when a non-redefiniable variable (e.g. .equiv
followed by .set; .weakref followed by .set).
Make MCAsmStreamer::emitLabel call setOffset to make the behavior
similar to MCObjectStreamer. `isUndefined()` can now be replaced with
`isUnset()`.
Additionally, fix an AMDGPU API user (tested by a few tests including
MC/AMDGPU/hsa-v4.s)
We report cyclic dependency errors for variable symbols and rely on
isSymbolUsedInExpression in parseAssignmentExpression at parse time,
which does not catch all setVariableValue cases (e.g. cyclic .weakref).
Instead, add a bit to MCSymbol and check it when walking the variable
value MCExpr. When a cycle is detected when we have a final layout,
report an error and set the variable to a constant to avoid duplicate
errors.
isSymbolUsedInExpression is considered deprecated, but it is still used
by AMDGPU (#112251).
Currently, the code path is likely only reachable with super edge-case scenario,
but will be more reachable with the upcoming parseAssignmentExpression improvement
to address a pile of hacks.
Use a variable symbol without any specifier instead of VK_WEAKREF.
Add code in ELFObjectWriter::executePostLayoutBinding to check
whether the target should be made an undefined weak symbol.
This change fixes several issues:
* Unreferenced `.weakref alias, target` no longer creates an undefined `target`.
* When `alias` is already defined, report an error instead of crashing.
.weakref is specific to ELF. llvm-ml has reused the VK_WEAKREF name for
a different concept. wasm incorrectly copied the ELF implementation.
Remove it.
Replace MCSymbol argument with MCValue::AddSym. The minor difference in
.weakref handling is negligible, as our implementation may not fully
align with GAS, and .weakref is not used in practice.
