This removes the only virtual function of MCSection.
NVPTXTargetStreamer::changeSection uses the MCSectionELF print method.
Change it to just print the section name.
Reland #150574 with a MCStreamer::changeSection change:
In Mach-O, DWARF sections use Begin as a temporary label, requiring a label
definition, unlike section symbols in other file formats.
(Tested by dec978036ef1037753e7de5b78c978e71c49217b)
---
13a79bbfe583e1d8cc85d241b580907260065eb8 (2017) introduced fragment
creation in MCContext for createELFSectionImpl, which was inappropriate.
Fragments should only be created when using MCSteramer, not during
`MCContext::get*Section` calls.
`initMachOMCObjectFileInfo` defines multiple sections, some of which may
not be used by the code generator. This caused symbol names matching
these sections to be incorrectly marked as undefined (see
https://reviews.llvm.org/D55173).
The fragment code was later replicated in other file formats, such as
WebAssembly (see https://reviews.llvm.org/D46561), XCOFF, and GOFF.
This patch fixes the problem by moving initial fragment allocation from
MCContext::createSection to MCStreamer::changeSection.
While MCContext still creates a section symbol, the symbol is not
attached to the initial fragment. In addition,
* Move `emitLabel`/`setFragment` from `switchSection*` and
overridden changeSection to `MCObjectStreamer::changeSection` for
consistency.
* De-virtualize `switchSectionNoPrint`.
* test/CodeGen/XCore/section-name.ll now passes. XCore doesn't support
MCObjectStreamer. I don't think the MCAsmStreamer output behavior
change matters.
Pull Request: https://github.com/llvm/llvm-project/pull/150574
The object file format specific derived classes are used in context like
MCStreamer and MCObjectTargetWriter where the type is statically known.
We don't use isa/dyn_cast and we want to eliminate
MCSection::SectionVariant in the base class.
13a79bbfe583e1d8cc85d241b580907260065eb8 (2017) introduced fragment
creation in MCContext for createELFSectionImpl, which was inappropriate.
Fragments should only be created when using MCSteramer, not during
`MCContext::get*Section` calls.
`initMachOMCObjectFileInfo` defines multiple sections, some of which may
not be used by the code generator. This caused symbol names matching
these sections to be incorrectly marked as undefined (see
https://reviews.llvm.org/D55173).
The fragment code was later replicated in other file formats, such as
WebAssembly (see https://reviews.llvm.org/D46561), XCOFF, and GOFF.
This patch fixes the problem by moving initial fragment allocation from
MCContext::createSection to MCStreamer::changeSection.
While MCContext still creates a section symbol, the symbol is not
attached to the initial fragment.
In addition, move `emitLabel`/`setFragment` from `switchSection*` and
overridden changeSection to `MCObjectStreamer::changeSection` for
consistency.
* test/CodeGen/XCore/section-name.ll now passes. XCore doesn't support
MCObjectStreamer. I don't think the MCAsmStreamer output behavior
change matters.
Pull Request: https://github.com/llvm/llvm-project/pull/150574
This reverts commit ad36e4284d66c3609ef8675ef02ff1844bc1951d, fixing a
single uninitialized bit (which cannot be detected with Address
Sanitizer).
This PR adds support for the llvm-mc command-line flag "--gsframe" and
adds ".sframe" to the legal values passed ".cfi_section". It plumbs the
option through the cfi handling code a fair amount. Code to support
actual section generation follows in a future PR.
These options match the gnu-assembler's support syntax for sframes, on
both the command line and in assembly files.
First in a series of changes that will allow llvm-mc to produce sframe
.cfi sections. For more information about sframes, see
https://sourceware.org/binutils/docs-2.44/sframe-spec.html
and the llvm-RFC here:
https://discourse.llvm.org/t/rfc-adding-sframe-support-to-llvm/86900
This PR adds support for the llvm-mc command-line flag "--gsframe" and
adds ".sframe" to the legal values passed ".cfi_section". It plumbs the
option through the cfi handling code a fair amount. Code to support
actual section generation follows in a future PR.
These options match the gnu-assembler's support syntax for sframes, on
both the command line and in assembly files.
First in a series of changes that will allow llvm-mc to produce sframe
.cfi sections. For more information about sframes, see
https://sourceware.org/binutils/docs-2.44/sframe-spec.html
and the llvm-RFC here:
https://discourse.llvm.org/t/rfc-adding-sframe-support-to-llvm/86900
They are specific to MCObjectStreamer and unneeded by MCAsmStreamer.
Add isObj() so that MCTargetAsmParser can determine whether the streamer
is MCObjectStreamer and conditionally call newFragment.
... by eagerly allocating an empty fragment when adding a fragment
with a variable-size tail.
X86AsmBackend, The JCC erratum mitigation and x86-pad-for-align set a
flag for FT_Relaxable, which needs to be moved to emitInstructionBegin.
```
if (CF->getKind() == MCFragment::FT_Relaxable)
CF->setAllowAutoPadding(canPadInst(Inst, OS));
```
Follow-up to #148544
First, avoid checking MCSubtargetInfo by reducing unnecessary overhead
introduced in https://reviews.llvm.org/D44928 . That change passed STI
to both FT_Data and FT_Relaxable fragments, but STI is only necessary
for FT_Relaxable.
The use of STI in FT_Data was added for:
* Bundle alignment mode, which has been removed (#148781).
* ARM, which inappropriately uses STI in `ARMAsmBackend::applyFixup` due
to tech debt, unlike other targets. All tests passed even without the
`copySTI` change.
To ensure safety, `copySTI` now starts a new fragment to prevent mixed
STI values.
Second, avoid checking LinkerRelaxable by eagerly starting a new
fragment when a FT_Data/FT_Align fragment is marked linker-relaxable.
There is currently an extra empty FT_Data if an alignment immediately
follows a linker-relaxable fragment, which will be improved in the
future when FT_Align information is moved to the variable-tail.
Pull Request: https://github.com/llvm/llvm-project/pull/149471
The being-removed PNaCl has a Software Fault Isolation mechanism, which
requires that certain instructions and groups of instructions do not
cross a bundle boundary. When `.bundle_align_mode` is in effect, each
instruction is placed in its own fragment, allowing flexible NOP
padding.
This feature has significantly complicated our refactoring of MCStreamer
and MCFragment, leading to considerable effort spent untangling
it (including flushPendingLabels (75006466296ed4b0f845cbbec4bf77c21de43b40),
MCAssembler iteration improvement, and recent MCFragment refactoring).
* Make MCObjectStreamer::emitInstToData non-virtual and delete
MCELFStreamer::emitInstTodata
* Delete MCELFStreamer::emitValueImpl and emitValueToAlignment
Minor instructions:u decrease for both -O0 -g and -O3 builds
https://llvm-compile-time-tracker.com/compare.php?from=c06d3a7b728293cbc53ff91239d6cd87c0982ffb&to=9b078c7f228bc5b6cdbfe839f751c9407f8aec3e&stat=instructions:u
Pull Request: https://github.com/llvm/llvm-project/pull/148781
* Rename the vague `Value` to `Fill`.
* FillLen is at most 8. Making the field smaller to facilitate encoding
MCAlignFragment as a MCFragment union member.
* Replace an unreachable report_fatal_error with assert.
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.
* Make relocation specifier code closer (MCAsmInfo defines specifiers).
* MCExpr::print has an optional MCAsmInfo argument, which is
error-prone when omitted.
* Enable MCSpecifierExpr
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.
The .syntax unified directive and .codeX/.code X directives are, other
than some simple common printing code, exclusively implemented in the
targets themselves. Thus, remove the corresponding MCAF_* flags and
reimplement the directives solely within the targets. This avoids
exposing all targets to all other targets' flags.
Since MCAF_SubsectionsViaSymbols is all that remains, convert it to its
own function like other directives, simplifying its implementation.
Note that, on X86, we now always need a target streamer when parsing
assembly, as it's now used for directives that aren't COFF-specific. It
still does not however need to do anything when producing a non-COFF
object file, so this commit does not introduce any new target streamers.
There is some churn in test output, and corresponding UTC regex changes,
due to comments no longer being flushed by these various directives (and
EmitEOL is not exposed outside MCAsmStreamer.cpp so we couldn't do so
even if we wanted to), but that was a bit odd to be doing anyway.
This is motivated by Morello LLVM, which adds yet another assembler flag
to distinguish A64 and C64 instruction sets, but did not update every
switch and so emits warnings during the build. Rather than fix those
warnings it seems better to instead make the problem not exist in the
first place via this change.
Adds support for emitting Windows x64 Unwind V2 information, includes
support `/d2epilogunwind` in clang-cl.
Unwind v2 adds information about the epilogs in functions such that the
unwinder can unwind even in the middle of an epilog, without having to
disassembly the function to see what has or has not been cleaned up.
Unwind v2 requires that all epilogs are in "canonical" form:
* If there was a stack allocation (fixed or dynamic) in the prolog, then
the first instruction in the epilog must be a stack deallocation.
* Next, for each `PUSH` in the prolog there must be a corresponding
`POP` instruction in exact reverse order.
* Finally, the epilog must end with the terminator.
This change adds a pass to validate epilogs in modules that have Unwind
v2 enabled and, if they pass, emits new pseudo instructions to MC that
1) note that the function is using unwind v2 and 2) mark the start of
the epilog (this is either the first `POP` if there is one, otherwise
the terminator instruction). If a function does not meet these
requirements, it is downgraded to Unwind v1 (i.e., these new pseudo
instructions are not emitted).
Note that the unwind v2 table only marks the size of the epilog in the
"header" unwind code, but it's possible for epilogs to use different
terminator instructions thus they are not all the same size. As a work
around for this, MC will assume that all terminator instructions are
1-byte long - this still works correctly with the Windows unwinder as it
is only using the size to do a range check to see if a thread is in an
epilog or not, and since the instruction pointer will never be in the
middle of an instruction and the terminator is always at the end of an
epilog the range check will function correctly. This does mean, however,
that the "at end" optimization (where an epilog unwind code can be
elided if the last epilog is at the end of the function) can only be
used if the terminator is 1-byte long.
One other complication with the implementation is that the unwind table
for a function is emitted during streaming, however we can't calculate
the distance between an epilog and the end of the function at that time
as layout hasn't been completed yet (thus some instructions may be
relaxed). To work around this, epilog unwind codes are emitted via a
fixup. This also means that we can't pre-emptively downgrade a function
to Unwind v1 if one of these offsets is too large, so instead we raise
an error (but I've passed through the location information, so the user
will know which of their functions is problematic).
Reland https://github.com/llvm/llvm-project/pull/106230
The original PR was reverted due to compilation time regression.
This PR fixed that by adding a condition OutStreamer->isVerboseAsm() to
the generation of extra inlined-at debug info, so that it does not
affect normal compilation time.
Currently MC print source location of instructions in comments in
assembly when debug info is available, however, it does not include
inlined-at locations when a function is inlined.
For example, function foo is defined in header file a.h and is called
multiple times in b.cpp. If foo is inlined, current assembly will only
show its instructions with their line numbers in a.h. With inlined-at
locations, the assembly will also show where foo is called in b.cpp.
This patch adds inlined-at locations to the comments by using
DebugLoc::print. It makes the printed source location info consistent
with those printed by machine passes.
Currently MC print source location of instructions in comments in
assembly when debug info is available, however, it does not include
inlined-at locations when a function is inlined.
For example, function foo is defined in header file a.h and is called
multiple times in b.cpp. If foo is inlined, current assembly will only
show its instructions with their line numbers in a.h. With inlined-at
locations, the assembly will also show where foo is called in b.cpp.
This patch adds inlined-at locations to the comments by using
DebugLoc::print. It makes the printed source location info consistent
with those printed by machine passes.
https://reviews.llvm.org/D23669 inappropriately added MIPS-specific
dtprel/tprel directives to MCStreamer. In addition,
llvm-mc -filetype=null parsing these directives will crash.
This patch moves these functions to MipsTargetStreamer and fixes
-filetype=null.
gprel32 and gprel64, called by AsmPrinter, are moved to
MCTargetStreamer.
MCStreamer should not declare arch-specific functions. Such functions
should go to MCTargetStreamer.
Move MCMachOStreamer::emitThumbFunc to ARMTargetMachOStreamer, which is
a new subclass of ARMTargetStreamer. (The new class is just placed in
ARMMachObjectWriter.cpp. The conventional split like
ARMELFObjectWriter.cpp/ARMELFObjectWriter.cpp is overkill.)
`emitCFILabel`, called by ARMWinCOFFStreamer.cpp, has to be made public.
Pull Request: https://github.com/llvm/llvm-project/pull/126199
Windows x64 Unwind V2 adds epilog information to unwind data:
specifically, the length of the epilog and the offset of each epilog.
The first step to do this is to add markers to the beginning and end of
each epilog when generating Windows x64 code. I've modelled this after
how LLVM was marking ARM and AArch64 epilogs in Windows (and unified the
code between the three).
This change implements import call optimization for AArch64 Windows
(equivalent to the undocumented MSVC `/d2ImportCallOptimization` flag).
Import call optimization adds additional data to the binary which can be
used by the Windows kernel loader to rewrite indirect calls to imported
functions as direct calls. It uses the same [Dynamic Value Relocation
Table mechanism that was leveraged on x64 to implement
`/d2GuardRetpoline`](https://techcommunity.microsoft.com/blog/windowsosplatform/mitigating-spectre-variant-2-with-retpoline-on-windows/295618).
The change to the obj file is to add a new `.impcall` section with the
following layout:
```cpp
// Per section that contains calls to imported functions:
// uint32_t SectionSize: Size in bytes for information in this section.
// uint32_t Section Number
// Per call to imported function in section:
// uint32_t Kind: the kind of imported function.
// uint32_t BranchOffset: the offset of the branch instruction in its
// parent section.
// uint32_t TargetSymbolId: the symbol id of the called function.
```
NOTE: If the import call optimization feature is enabled, then the
`.impcall` section must be emitted, even if there are no calls to
imported functions.
The implementation is split across a few parts of LLVM:
* During AArch64 instruction selection, the `GlobalValue` for each call
to a global is recorded into the Extra Information for that node.
* During lowering to machine instructions, the called global value for
each call is noted in its containing `MachineFunction`.
* During AArch64 asm printing, if the import call optimization feature
is enabled:
- A (new) `.impcall` directive is emitted for each call to an imported
function.
- The `.impcall` section is emitted with its magic header (but is not
filled in).
* During COFF object writing, the `.impcall` section is filled in based
on each `.impcall` directive that were encountered.
The `.impcall` section can only be filled in when we are writing the
COFF object as it requires the actual section numbers, which are only
assigned at that point (i.e., they don't exist during asm printing).
I had tried to avoid using the Extra Information during instruction
selection and instead implement this either purely during asm printing
or in a `MachineFunctionPass` (as suggested in [on the
forums](https://discourse.llvm.org/t/design-gathering-locations-of-instructions-to-emit-into-a-section/83729/3))
but this was not possible due to how loading and calling an imported
function works on AArch64. Specifically, they are emitted as `ADRP` +
`LDR` (to load the symbol) then a `BR` (to do the call), so at the point
when we have machine instructions, we would have to work backwards
through the instructions to discover what is being called. An initial
prototype did work by inspecting instructions; however, it didn't
correctly handle the case where the same function was called twice in a
row, which caused LLVM to elide the `ADRP` + `LDR` and reuse the
previously loaded address. Worse than that, sometimes for the
double-call case LLVM decided to spill the loaded address to the stack
and then reload it before making the second call. So, instead of trying
to implement logic to discover where the value in a register came from,
I instead recorded the symbol being called at the last place where it
was easy to do: instruction selection.
llvm-mc --assemble prints an initial `.text` from `initSections`.
This is weird for quick assembly tasks that do not specify `.text`.
Omit the .text by moving section directive printing from `changeSection`
to `switchSection`. switchSectionNoPrint now correctly calls the
`changeSection` hook (needed by MachO).
The initial directives of clang -S are now reordered. On ELF targets, we
get `.file "a.c"; .text` instead of `.text; .file "a.c"`.
If there is no function, `.text` will be omitted.
**Summary**
This patch introduces a new compiler option `-mllvm
-emit-func-debug-line-table-offsets` that enables the emission of
per-function line table offsets and end sequences in DWARF debug
information. This enhancement allows tools and debuggers to accurately
attribute line number information to their corresponding functions, even
in scenarios where functions are merged or share the same address space
due to optimizations like Identical Code Folding (ICF) in the linker.
**Background**
RFC: [New DWARF Attribute for Symbolication of Merged
Functions](https://discourse.llvm.org/t/rfc-new-dwarf-attribute-for-symbolication-of-merged-functions/79434)
Previous similar PR:
[#93137](https://github.com/llvm/llvm-project/pull/93137) – This PR was
very similar to the current one but at the time, the assembler had no
support for emitting labels within the line table. That support was
added in PR [#99710](https://github.com/llvm/llvm-project/pull/99710) -
and in this PR we use some of the support added in the assembler PR.
In the current implementation, Clang generates line information in the
`debug_line` section without directly associating line entries with
their originating `DW_TAG_subprogram` DIEs. This can lead to issues when
post-compilation optimizations merge functions, resulting in overlapping
address ranges and ambiguous line information.
For example, when functions are merged by ICF in LLD, multiple functions
may end up sharing the same address range. Without explicit linkage
between functions and their line entries, tools cannot accurately
attribute line information to the correct function, adversely affecting
debugging and call stack resolution.
**Implementation Details**
To address the above issue, the patch makes the following key changes:
**`DW_AT_LLVM_stmt_sequence` Attribute**: Introduces a new LLVM-specific
attribute `DW_AT_LLVM_stmt_sequence` to each `DW_TAG_subprogram` DIE.
This attribute holds a label pointing to the offset in the line table
where the function's line entries begin.
**End-of-Sequence Markers**: Emits an explicit DW_LNE_end_sequence after
each function's line entries in the line table. This marks the end of
the line information for that function, ensuring that line entries are
correctly delimited.
**Assembler and Streamer Modifications**: Modifies the MCStreamer and
related classes to support emitting the necessary labels and tracking
the current function's line entries. A new flag
GenerateFuncLineTableOffsets is added to control this behavior.
**Compiler Option**: Introduces the `-mllvm
-emit-func-debug-line-table-offsets` option to enable this
functionality, allowing users to opt-in as needed.
These specify that the value of the given register in the previous frame
is the CFA plus some offset. This isn't very common but can be necessary
if the original value is normally reconstructed from the stack/frame
pointer instead of being saved on the stack and reloaded from there.
As part of FEAT_PAuthLR, a new DWARF Frame Instruction was introduced,
`DW_CFA_AARCH64_negate_ra_state_with_pc`. This instructs Libunwind that
the PC has been used with the signing instruction. This change includes
three commits
- Libunwind support for the newly introduced DWARF Instruction
- CodeGen Support for the DWARF Instructions
- Reversing the changes made in #96377. Due to
`DW_CFA_AARCH64_negate_ra_state_with_pc`'s requirements to be placed
immediately after the signing instruction, this would mean the CFI
Instruction location was not consistent with the generated location when
not using FEAT_PAuthLR. The commit reverses the changes and makes the
location consistent across the different branch protection options.
While this does have a code size effect, this is a negligible one.
For the ABI information, see here:
853286c7ab/aadwarf64/aadwarf64.rst (id23)
GNU assembler 2.26 introduced the .cfi_label directive. It does not
expand to any CFI instructions, but defines a label in
.eh_frame/.debug_frame, which can be used by runtime patching code to
locate the FDE. .cfi_label is not allowed for CIE's initial
instructions, and can therefore be used to force the next instruction to
be placed in a FDE instead of a CIE.
In glibc since 2018, sysdeps/riscv/start.S utilizes .cfi_label to force
DW_CFA_undefined to be placed in a FDE. arc/csky/loongarch ports have
copied this use.
```
.cfi_startproc
// DW_CFA_undefined is allowed for CIE's initial instructions.
// Without .cfi_label, gas would place DW_CFA_undefined in a CIE.
.cfi_label .Ldummy
.cfi_undefined ra
.cfi_endproc
```
No CFI instruction is associated with .cfi_label, so the `case
MCCFIInstruction::OpLabel:` code in BOLT is unreachable and onlt to make
-Wswitch happy.
Close#97222
Pull Request: https://github.com/llvm/llvm-project/pull/97922
21101b32318647f600584d966c697d8773f59629 (2013) added SymbolOrdering,
which essentially became useless when
e3a20f57d927e422874a8e7730bb7590515b586d (2015) removed `AssignSection`
from `EmitLabel`. `assignFragment` is still used in very few places like
emitTBSSSymbol, which do not make a difference if we remove
SymbolOrdering.
Follow-up to 05ba5c0648ae5e80d5afce270495bf3b1eef9af4. uint32_t is
preferred over const MCExpr * in the section stack uses because it
should only be evaluated once. Change the paramter type to match.
There are only three actual uses of the section kind in MCSection:
isText(), XCOFF, and WebAssembly. Store isText() in the MCSection, and
store other info in the actual section variants where required.
ELF and COFF flags also encode all relevant information, so for these
two section variants, remove the SectionKind parameter entirely.
This allows to remove the string switch (which is unnecessary and
inaccurate) from createELFSectionImpl. This was introduced in
[D133456](https://reviews.llvm.org/D133456), but apparently, it was
never hit for non-writable sections anyway and the resulting kind was
never used.
Commit 6c0665e22174d474050e85ca367424f6e02476be
(https://reviews.llvm.org/D45164) enabled certain constant expression
evaluation for `MCObjectStreamer` at parse time (e.g. `.if` directives,
see llvm/test/MC/AsmParser/assembler-expressions.s).
`getUseAssemblerInfoForParsing` was added to make `clang -c` handling
inline assembly similar to `MCAsmStreamer` (e.g. `llvm-mc -filetype=asm`),
where such expression folding (related to
`AttemptToFoldSymbolOffsetDifference`) is unavailable.
I believe this is overly conservative. We can make some parse-time
expression folding work for `clang -c` even if `clang -S` would still
report an error, a MCAsmStreamer issue (we cannot print `.if`
directives) that should not restrict the functionality of
MCObjectStreamer.
```
% cat b.cc
asm(R"(
.pushsection .text,"ax"
.globl _start; _start: ret
.if . -_start == 1
ret
.endif
.popsection
)");
% gcc -S b.cc && gcc -c b.cc
% clang -S -fno-integrated-as b.cc # succeeded
% clang -c b.cc # succeeded with this patch
% clang -S b.cc # still failed
<inline asm>:4:5: error: expected absolute expression
4 | .if . -_start == 1
| ^
1 error generated.
```
However, removing `getUseAssemblerInfoForParsing` would make
MCDwarfFrameEmitter::Emit (for .eh_frame FDE) slow (~4% compile time
regression for sqlite3.c amalgamation) due to expensive
`AttemptToFoldSymbolOffsetDifference`. For now, make
`UseAssemblerInfoForParsing` false in MCDwarfFrameEmitter::Emit.
Close#62520
Link: https://discourse.llvm.org/t/rfc-clang-assembly-object-equivalence-for-files-with-inline-assembly/78841
Pull Request: https://github.com/llvm/llvm-project/pull/91082
This reverts commit 03c53c69a367008da689f0d2940e2197eb4a955c.
This causes very large compile-time regressions in some cases,
e.g. sqlite3 at O0 regresses by 5%.
Commit 6c0665e22174d474050e85ca367424f6e02476be
(https://reviews.llvm.org/D45164) enabled certain constant expression
evaluation for `MCObjectStreamer` at parse time (e.g. `.if` directives,
see llvm/test/MC/AsmParser/assembler-expressions.s).
`getUseAssemblerInfoForParsing` was added to make `clang -c` handling
inline assembly similar to `MCAsmStreamer` (e.g. `llvm-mc -filetype=asm`),
where such expression folding (related to
`AttemptToFoldSymbolOffsetDifference`) is unavailable.
I believe this is overly conservative. We can make some parse-time
expression folding work for `clang -c` even if `clang -S` would still
report an error, a MCAsmStreamer issue (we cannot print `.if`
directives) that should not restrict the functionality of
MCObjectStreamer.
```
% cat b.cc
asm(R"(
.pushsection .text,"ax"
.globl _start; _start: ret
.if . -_start == 1
ret
.endif
.popsection
)");
% gcc -S b.cc && gcc -c b.cc
% clang -S -fno-integrated-as b.cc # succeeded
% clang -c b.cc # succeeded with this patch
% clang -S b.cc # still failed
<inline asm>:4:5: error: expected absolute expression
4 | .if . -_start == 1
| ^
1 error generated.
```
Close#62520
Link: https://discourse.llvm.org/t/rfc-clang-assembly-object-equivalence-for-files-with-inline-assembly/78841
Pull Request: https://github.com/llvm/llvm-project/pull/91082
