COFF has a verifier check that private global variables don't have a comdat of the same name.
Reviewed By: rnk
Differential Revision: https://reviews.llvm.org/D131043
Profiling stopped working for us after D98061, which was largely a
Fuschia-specific patch but in one place used `isOSBinFormatELF` to
make a decision. I'm adding a PS4/PS5 exception to that, so we can
get profiling to work again.
Differential Revision: https://reviews.llvm.org/D127506
Profiling stopped working for us after D98061, which was largely a
Fuschia-specific patch but in one place used `isOSBinFormatELF` to
make a decision. I'm adding a PS4/PS5 exception to that, so we can
get profiling to work again.
Differential Revision: https://reviews.llvm.org/D127506
This patch switches the PGO implementation on AIX from using the runtime
registration-based section tracking to the __start_SECNAME/__stop_SECNAME
based. In order to enable the recognition of __start_SECNAME/__stop_SECNAME
symbols in the AIX linker, the -bdbg:namedsects:ss needs to be used.
Reviewed By: jsji, MaskRay, davidxl
Differential Revision: https://reviews.llvm.org/D124857
LTO objects might compiled with different `mbranch-protection` flags which will cause an error in the linker.
Such a setup is allowed in the normal build with this change that is possible.
Reviewed By: pcc
Differential Revision: https://reviews.llvm.org/D123493
NVPTX does not support generating binary files, which is required for
these tests.
The majority of tests in 'DebugInfo/Generic' also require emitting
object files, so they all are disabled for NVPTX.
Differential Revision: https://reviews.llvm.org/D121996
Use the llvm flag `-pgo-function-entry-coverage` to create single byte "counters" to track functions coverage. This mode has significantly less size overhead in both code and data because
* We mark a function as "covered" with a store instead of an increment which generally requires fewer assembly instructions
* We use a single byte per function rather than 8 bytes per block
The trade off of course is that this mode only tells you if a function has been covered. This is useful, for example, to detect dead code.
When combined with debug info correlation [0] we are able to create an instrumented Clang binary that is only 150M (the vanilla Clang binary is 143M). That is an overhead of 7M (4.9%) compared to the default instrumentation (without value profiling) which has an overhead of 31M (21.7%).
[0] https://groups.google.com/g/llvm-dev/c/r03Z6JoN7d4
Reviewed By: kyulee
Differential Revision: https://reviews.llvm.org/D116180
Add the llvm flag `-debug-info-correlate` to attach debug info to instrumentation counters so we can correlate raw profile data to their functions. Raw profiles are dumped as `.proflite` files. The next diff enables `llvm-profdata` to consume `.proflite` and debug info files to produce a normal `.profdata` profile.
Part of the "lightweight instrumentation" work: https://groups.google.com/g/llvm-dev/c/r03Z6JoN7d4
The original diff https://reviews.llvm.org/D114565 was reverted because of the `Instrumentation/InstrProfiling/debug-info-correlate.ll` test, which is fixed in this commit.
Reviewed By: kyulee
Differential Revision: https://reviews.llvm.org/D115693
This reverts commit 800bf8ed29.
The `Instrumentation/InstrProfiling/debug-info-correlate.ll` test was
failing because I forgot the `llc` commands are architecture specific.
I'll follow up with a fix.
Differential Revision: https://reviews.llvm.org/D115689
Add the llvm flag `-debug-info-correlate` to attach debug info to instrumentation counters so we can correlate raw profile data to their functions. Raw profiles are dumped as `.proflite` files. The next diff enables `llvm-profdata` to consume `.proflite` and debug info files to produce a normal `.profdata` profile.
Part of the "lightweight instrumentation" work: https://groups.google.com/g/llvm-dev/c/r03Z6JoN7d4
Reviewed By: kyulee
Differential Revision: https://reviews.llvm.org/D114565
The `llvm.instrprof.increment` intrinsic uses `i32` for the index. We should use this same type for the index into the GEP instructions.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D114268
We generate symbols like `profc`/`profd` for each function, and put them into csects.
When there are weak functions, we generate weak symbols for the functions as well,
with ELF (and some others), linker (binder) will discard and only keep one copy of the weak symbols.
However, on AIX, the current binder can NOT discard the weak symbols if we put all of them into the same csect,
as binder can NOT discard a subset of a csect.
This creates a unique challenge for using those symbols to calculate some relative offsets.
This patch changed the linkage of `profc`/`profd` symbols to be private, so that all the profc/profd for each weak symbol will be *local* to objects, and all kept in the csect, so we won't have problem. Although only one of the counters will be used, all the pointer in the profd is correct.
The downside is that we won't be able to discard the duplicated counters and profile data,
but those can not be discarded even if we keep the weak linkage,
due to the binder limitation of not discarding a subsect of the csect either .
Reviewed By: Whitney, MaskRay
Differential Revision: https://reviews.llvm.org/D110422
Similar to D97585.
D25456 used `S_ATTR_LIVE_SUPPORT` to ensure the data variable will be retained
or discarded as a unit with the counter variable, so llvm.compiler.used is
sufficient. It allows ld to dead strip unneeded profc and profd variables.
Reviewed By: vsk
Differential Revision: https://reviews.llvm.org/D105445
This reverts commit f653beea88.
It broke Windows coverage-inline.cpp because link.exe has a limitation
that external symbols in IMAGE_COMDAT_SELECT_ASSOCIATIVE don't work.
It essentially dropped the previous size optimization for coverage
because coverage doesn't rename comdat by default.
Needs more investigation what we should do.
The NS==0 condition used by D103717 missed a corner case: if the current copy
does not have a hash suffix (e.g. weak_odr), a copy with value profiling (with a
different CFG) may exist. This is super rare, but is possible with pre-inlining
PGO instrumentation (which can make a weak_odr function inlines its callees
differently, sometimes with value profiling while sometimes without).
If the current copy with private profd is prevailing, the non-prevailing copy
may get an undefined symbol if a caller inlining the non-prevailing function
references its profd. If the other copy with non-private profd is prevailing,
the current copy may cause a "relocation to discarded section" linker error.
The fix is straightforward: just keep non-private profd in this case.
With this change, a stage 2 (`-DLLVM_TARGETS_TO_BUILD=X86 -DLLVM_BUILD_INSTRUMENTED=IR`)
clang is 0.08% larger (172431496/172286720-1).
`stat -c %s **/*.o | awk '{s+=$1}END{print s}' is 0.026% larger.
The majority of D103717's benefits remains.
Reviewed By: xur
Differential Revision: https://reviews.llvm.org/D108432
We found that AIX was not covered in most of the InstrProfiling tests.
So we are trying to enable the tests gradually.
This is to add AIX triple to platform tests to make sure the
registrations are OK.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D108490
The COFF specific `DataReferencedByCode` complexity (D103372 D103717) is due to
a link.exe limitation: an external symbol in IMAGE_COMDAT_SELECT_ASSOCIATIVE is
not really dropped, so it can cause duplicate definition error.
When none of the translation units in the binary have been instrumented
we shouldn't need to link the profile runtime. However, because we pass
-u__llvm_profile_runtime on Linux and Fuchsia, the runtime would still
be pulled in and incur some overhead. On Fuchsia which uses runtime
counter relocation, it also means that we cannot reference the bias
variable unconditionally.
This change modifies the InstrProfiling pass to pull in the profile
runtime only when needed by declaring the __llvm_profile_runtime symbol
in the translation unit only when needed. For now we restrict this only
for Fuchsia, but this can be later expanded to other platforms. This
approach was already used prior to 9a041a7522, but we changed it
to always generate the __llvm_profile_runtime due to a TAPI limitation,
but that limitation may no longer apply, and it certainly doesn't apply
on platforms like Fuchsia.
Differential Revision: https://reviews.llvm.org/D98061
Rather than emitting the bias variable lazily as needed, emit it
eagerly. This allows profile runtime to refer to this variable
unconditionally without having to use the weak reference. The bias
variable is in a COMDAT so there'll never be more than one instance,
and if it's not needed, linker should be able to GC it, so the overhead
should be minimal.
Differential Revision: https://reviews.llvm.org/D107377
Change `CountersPtr` in `__profd_` to a label difference, which is a link-time
constant. On ELF, when linking a shared object, this requires that `__profc_` is
either private or linkonce/linkonce_odr hidden. On COFF, we need D104564 so that
`.quad a-b` (64-bit label difference) can lower to a 32-bit PC-relative relocation.
```
# ELF: R_X86_64_PC64 (PC-relative)
.quad .L__profc_foo-.L__profd_foo
# Mach-O: a pair of 8-byte X86_64_RELOC_UNSIGNED and X86_64_RELOC_SUBTRACTOR
.quad l___profc_foo-l___profd_foo
# COFF: we actually use IMAGE_REL_AMD64_REL32/IMAGE_REL_ARM64_REL32 so
# the high 32-bit value is zero even if .L__profc_foo < .L__profd_foo
# As compensation, we truncate CountersDelta in the header so that
# __llvm_profile_merge_from_buffer and llvm-profdata reader keep working.
.quad .L__profc_foo-.L__profd_foo
```
(Note: link.exe sorts `.lprfc` before `.lprfd` even if the object writer
has `.lprfd` before `.lprfc`, so we cannot work around by reordering
`.lprfc` and `.lprfd`.)
With this change, a stage 2 (`-DLLVM_TARGETS_TO_BUILD=X86 -DLLVM_BUILD_INSTRUMENTED=IR`)
`ld -pie` linked clang is 1.74% smaller due to fewer R_X86_64_RELATIVE relocations.
```
% readelf -r pie | awk '$3~/R.*/{s[$3]++} END {for (k in s) print k, s[k]}'
R_X86_64_JUMP_SLO 331
R_X86_64_TPOFF64 2
R_X86_64_RELATIVE 476059 # was: 607712
R_X86_64_64 2616
R_X86_64_GLOB_DAT 31
```
The absolute function address (used by llvm-profdata to collect indirect call
targets) can be converted to relative as well, but is not done in this patch.
Differential Revision: https://reviews.llvm.org/D104556
In the textual format, `noduplicates` means no COMDAT/section group
deduplication is performed. Therefore, if both sets of sections are retained, and
they happen to define strong external symbols with the same names,
there will be a duplicate definition linker error.
In PE/COFF, the selection kind lowers to `IMAGE_COMDAT_SELECT_NODUPLICATES`.
The name describes the corollary instead of the immediate semantics. The name
can cause confusion to other binary formats (ELF, wasm) which have implemented/
want to implement the "no deduplication" selection kind. Rename it to be clearer.
Reviewed By: rnk
Differential Revision: https://reviews.llvm.org/D106319
We need the compiler generated variable to override the weak symbol of
the same name inside the profile runtime, but using LinkOnceODRLinkage
results in weak symbol being emitted in which case the symbol selected
by the linker is going to depend on the order of inputs which can be
fragile.
This change replaces the use of weak definition inside the runtime with
a weak alias. We place the compiler generated symbol inside a COMDAT
group so dead definition can be garbage collected by the linker.
We also disable the use of runtime counter relocation on Darwin since
Mach-O doesn't support weak external references, but Darwin already uses
a different continous mode that relies on overmapping so runtime counter
relocation isn't needed there.
Differential Revision: https://reviews.llvm.org/D105176
We need the compiler generated variable to override the weak symbol of
the same name inside the profile runtime, but using LinkOnceODRLinkage
results in weak symbol being emitted which leads to an issue where the
linker might choose either of the weak symbols potentially disabling the
runtime counter relocation.
This change replaces the use of weak definition inside the runtime with
an external weak reference to address the issue. We also place the
compiler generated symbol inside a COMDAT group so dead definition can
be garbage collected by the linker.
Differential Revision: https://reviews.llvm.org/D105176
`__profd_*` variables are referenced by code only when value profiling is
enabled. If disabled (e.g. default -fprofile-instr-generate), the symbols just
waste space on ELF/Mach-O. We change the comdat symbol from `__profd_*` to
`__profc_*` because an internal symbol does not provide deduplication features
on COFF. The choice doesn't matter on ELF.
(In -DLLVM_BUILD_INSTRUMENTED_COVERAGE=on build, there is now no `__profd_*` symbols.)
On Windows this enables further optimization. We are no longer affected by the
link.exe limitation: an external symbol in IMAGE_COMDAT_SELECT_ASSOCIATIVE can
cause duplicate definition error.
https://lists.llvm.org/pipermail/llvm-dev/2021-May/150758.html
We can thus use llvm.compiler.used instead of llvm.used like ELF (D97585).
This avoids many `/INCLUDE:` directives in `.drectve`.
Here is rnk's measurement for Chrome:
```
This reduced object file size of base_unittests.exe, compiled with coverage, optimizations, and gmlt debug info by 10%:
#BEFORE
$ find . -iname '*.obj' | xargs du -b | awk '{ sum += $1 } END { print sum}'
1047758867
$ du -cksh base_unittests.exe
82M base_unittests.exe
82M total
# AFTER
$ find . -iname '*.obj' | xargs du -b | awk '{ sum += $1 } END { print sum}'
937886499
$ du -cksh base_unittests.exe
78M base_unittests.exe
78M total
```
The change is NFC for Mach-O.
Reviewed By: davidxl, rnk
Differential Revision: https://reviews.llvm.org/D103372
`__profd_*` variables are referenced by code only when value profiling is
enabled. If disabled (e.g. default -fprofile-instr-generate), the symbols just
waste space on ELF/Mach-O. We change the comdat symbol from `__profd_*` to
`__profc_*` because an internal symbol does not provide deduplication features
on COFF. The choice doesn't matter on ELF.
(In -DLLVM_BUILD_INSTRUMENTED_COVERAGE=on build, there is now no `__profd_*` symbols.)
On Windows this enables further optimization. We are no longer affected by the
link.exe limitation: an external symbol in IMAGE_COMDAT_SELECT_ASSOCIATIVE can
cause duplicate definition error.
https://lists.llvm.org/pipermail/llvm-dev/2021-May/150758.html
We can thus use llvm.compiler.used instead of llvm.used like ELF (D97585).
This avoids many `/INCLUDE:` directives in `.drectve`.
Here is rnk's measurement for Chrome:
```
This reduced object file size of base_unittests.exe, compiled with coverage, optimizations, and gmlt debug info by 10%:
#BEFORE
$ find . -iname '*.obj' | xargs du -b | awk '{ sum += $1 } END { print sum}'
1047758867
$ du -cksh base_unittests.exe
82M base_unittests.exe
82M total
# AFTER
$ find . -iname '*.obj' | xargs du -b | awk '{ sum += $1 } END { print sum}'
937886499
$ du -cksh base_unittests.exe
78M base_unittests.exe
78M total
```
Reviewed By: davidxl, rnk
Differential Revision: https://reviews.llvm.org/D103372
The linkage/visibility of `__profn_*` variables are derived
from the profiled functions.
extern_weak => linkonce
available_externally => linkonce_odr
internal => private
extern => private
_ => unchanged
The linkage/visibility of `__profc_*`/`__profd_*` variables are derived from
`__profn_*` with linkage/visibility wrestling for Windows.
The changes can be folded to the following without changing semantics.
```
if (TT.isOSBinFormatCOFF() && !NeedComdat) {
Linkage = GlobalValue::InternalLinkage;
Visibility = GlobalValue::DefaultVisibility;
}
```
That said, I think we can just delete the code block.
An extern/internal function will now use private `__profc_*`/`__profd_*`
variables, instead of internal ones. This saves some symbol table entries.
A non-comdat {linkonce,weak}_odr function will now use hidden external
`__profc_*`/`__profd_*` variables instead of internal ones. There is potential
object file size increase because such symbols need `/INCLUDE:` directives.
However such non-comdat functions are rare (note that non-comdat weak
definitions don't prevent duplicate definition error).
The behavior changes match ELF.
Reviewed By: rnk
Differential Revision: https://reviews.llvm.org/D103355
* Change linkage/visibility of __profn_ variables to match the reality
* alwaysinline.ll: Add "EnableValueProfiling", otherwise it doesn't test available_externally alwaysinline.
* Delete PR23499.ll - covered by other comdat tests.
This broke the check-profile tests on Mac, see comment on the code
review.
> This is no longer needed, we can add __llvm_profile_runtime directly
> to llvm.compiler.used or llvm.used to achieve the same effect.
>
> Differential Revision: https://reviews.llvm.org/D98325
This reverts commit c7712087cb.
Also reverting the dependent follow-up commit:
Revert "[InstrProfiling] Generate runtime hook for ELF platforms"
> When using -fprofile-list to selectively apply instrumentation only
> to certain files or functions, we may end up with a binary that doesn't
> have any counters in the case where no files were selected. However,
> because on Linux and Fuchsia, we pass -u__llvm_profile_runtime, the
> runtime would still be pulled in and incur some non-trivial overhead,
> especially in the case when the continuous or runtime counter relocation
> mode is being used. A better way would be to pull in the profile runtime
> only when needed by declaring the __llvm_profile_runtime symbol in the
> translation unit only when needed.
>
> This approach was already used prior to 9a041a7522, but we changed it
> to always generate the __llvm_profile_runtime due to a TAPI limitation.
> Since TAPI is only used on Mach-O platforms, we could use the early
> emission of __llvm_profile_runtime there, and on other platforms we
> could change back to the earlier approach where the symbol is generated
> later only when needed. We can stop passing -u__llvm_profile_runtime to
> the linker on Linux and Fuchsia since the generated undefined symbol in
> each translation unit that needed it serves the same purpose.
>
> Differential Revision: https://reviews.llvm.org/D98061
This reverts commit 87fd09b25f.
When using -fprofile-list to selectively apply instrumentation only
to certain files or functions, we may end up with a binary that doesn't
have any counters in the case where no files were selected. However,
because on Linux and Fuchsia, we pass -u__llvm_profile_runtime, the
runtime would still be pulled in and incur some non-trivial overhead,
especially in the case when the continuous or runtime counter relocation
mode is being used. A better way would be to pull in the profile runtime
only when needed by declaring the __llvm_profile_runtime symbol in the
translation unit only when needed.
This approach was already used prior to 9a041a7522, but we changed it
to always generate the __llvm_profile_runtime due to a TAPI limitation.
Since TAPI is only used on Mach-O platforms, we could use the early
emission of __llvm_profile_runtime there, and on other platforms we
could change back to the earlier approach where the symbol is generated
later only when needed. We can stop passing -u__llvm_profile_runtime to
the linker on Linux and Fuchsia since the generated undefined symbol in
each translation unit that needed it serves the same purpose.
Differential Revision: https://reviews.llvm.org/D98061
This is no longer needed, we can add __llvm_profile_runtime directly
to llvm.compiler.used or llvm.used to achieve the same effect.
Differential Revision: https://reviews.llvm.org/D98325
`__llvm_prf_vnodes` and `__llvm_prf_names` are used by runtime but not
referenced via relocation in the translation unit.
With `-z start-stop-gc` (LLD 13 (D96914); GNU ld 2.37 https://sourceware.org/bugzilla/show_bug.cgi?id=27451),
the linker does not let `__start_/__stop_` references retain their sections.
Place `__llvm_prf_vnodes` and `__llvm_prf_names` in `llvm.used` to make
them retained by the linker.
This patch changes most existing `UsedVars` cases to `CompilerUsedVars`
to reflect the ideal state - if the binary format properly supports
section based GC (dead stripping), `llvm.compiler.used` should be sufficient.
`__llvm_prf_vnodes` and `__llvm_prf_names` are switched to `UsedVars`
since we want them to be unconditionally retained by both compiler and linker.
Behaviors on COFF/Mach-O are not affected.
Reviewed By: davidxl
Differential Revision: https://reviews.llvm.org/D97649
Arthur Eubanks