Many profitable optimizations cannot be performed at -Oz, due to
unrotated loops. While this is worse for size (minimally), many of the
optimizations significantly reduce code size, such as memcpy
optimizations and other patterns found by loop idiom recognition.
Related discussion can be found in issue #50308.
This patch adds an experimental, backend-only flag to allow loop header
duplication, regardless of the optimization level. Downstream consumers
can experiment with this flag, and if it is profitable, we can adjust
the compiler's defaults accordingly, and expose any useful frontend
flags to opt into the new behavior.
The pass itself checks whether to apply the optimization based on the
minsize attribute, so there isn't much functional benefit to preventing
the pass from being added. Gating the pass gets added to the pass
pipeline complicates the interaction with -enable-dfa-jump-thread, as
well.
Reviewers: aeubanks
Reviewed By: aeubanks
Pull Request: https://github.com/llvm/llvm-project/pull/83318
The performance of cold functions shouldn't matter too much, so if we
care about binary sizes, add an option to mark cold functions as
optsize/minsize for binary size, or optnone for compile times [1]. Clang
patch will be in a future patch.
This is intended to replace `shouldOptimizeForSize(Function&, ...)`.
We've seen multiple cases where calls to this expensive function, if not
careful, can blow up compile times. I will clean up users of that
function in a followup patch.
Initial version: https://reviews.llvm.org/D149800
[1]
https://discourse.llvm.org/t/rfc-new-feature-proposal-de-optimizing-cold-functions-using-pgo-info/56388
Add a pass to convert jump tables to switches.
The new pass replaces an indirect call with a switch + direct calls if all the functions in the jump table are smaller than the provided threshold.
The pass is currently disabled by default and can be enabled by -enable-jump-table-to-switch.
Test plan: ninja check-all
Currently, the UnifiedLTO pipeline seems to have trouble with several
LTO features, like SplitLTO units, which means we cannot use important
optimizations like Whole Program Devirtualization or security hardening
instrumentation like CFI.
This patch reverts FatLTO to using distinct pipelines for Full LTO and
ThinLTO. It still avoids module cloning, since that was error prone.
- With PGO, indirect call edges are constructed using value profiles, and the profile address is mapped to a function's PGO name. The PGO name is computed using a functions linkage before LTO internalization or global promotion.
- With ThinLTO, local functions [could be
promoted](2663d2cb9c/llvm/lib/Transforms/Utils/FunctionImportUtils.cpp (L288)) to have external linkage; and with
[full](2663d2cb9c/llvm/lib/LTO/LTO.cpp (L1328))
or
[thin](2663d2cb9c/llvm/lib/LTO/LTO.cpp (L448))
LTO, global functions could be internalized. Edge construction should use a function's PGO name before its linkage is updated.
Akin other passes - refactored the name to `InstrProfilingLoweringPass` to better communicate what it does, and split the pass part and the transformation part to avoid needing to initialize object state during `::run`.
A subsequent PR will move `InstrLowering` to the .cpp file and rename it to `InstrLowerer`.
https://github.com/llvm/llvm-project/issues/70703 pointed out that
cloning LLVM modules could lead to miscompiles when using FatLTO.
This is due to an existing issue when cloning modules with labels (see
#55991 and #47769). Since this can lead to miscompilation, we can avoid
cloning the LLVM modules, which was desirable anyway.
This patch modifies the EmbedBitcodePass to no longer clone the module
or run an input pipeline over it. Further, it make FatLTO always perform
UnifiedLTO, so we can still defer the Thin/Full LTO decision to
link-time. Lastly, it removes dead/obsolete code related to now defunct
options that do not work with the EmbedBitcodePass implementation any
longer.
Loosen up the matching so that a missing leaf debug frame in the profile
does not prevent matching an allocation context if we can match further
up the inlined call context. This relies on the pre-inliner, which was
already the default when performing normal PGO feedback along with the
MemProf feedback, but to ensure matching is not affected by the presence
of PGO, enable the pre-inliner for MemProf feedback as well.
See RFC for details:
https://discourse.llvm.org/t/rfc-for-moving-swift-s-merge-function-pass-to-llvm/73778
We will need to refactor extension to FunctionComparator/FunctionHash to
StructuralHash. This patch adds a new pass which is ported from Swift,
and will need to discuss on how to migrate Swift’s pass over after we
land this in llvm.
Create this PR to get some early review on the patch.
---------
Co-authored-by: Manman Ren <mren@meta.com>
This reverts commit 86bfeb906e3a95ae428f3e97d78d3d22a7c839f3.
This is a long time coming re-application that was originally reverted due to
regressions, unrelated to the actual inlining change. These regressions have since
been fixed due to another long-in-the-making change of a66051c6 landing.
Original commit message for reference:
---
We have several situations where it's beneficial for code size to ensure that every
call to always-inline functions are inlined before normal inlining decisions are
made. While the normal inliner runs in a "MandatoryOnly" mode to try to do this,
it only does it on a per-SCC basis, rather than the whole module. Ensuring that
all mandatory inlinings are done before any heuristic based decisions are made
just makes sense.
Despite being referred to the "legacy" AlwaysInliner pass, it's already necessary
for -O0 because the CGSCC inliner is too expensive in compile time to run at -O0.
This also fixes an exponential compile time blow up in
https://github.com/llvm/llvm-project/issues/59126
Differential Revision: https://reviews.llvm.org/D143624
---
This patch adds the LLVM changes needed for enabling HIP parallel algorithm offload on AMDGPU targets. What we do here is add two passes, one mandatory and one optional:
1. HipStdParAcceleratorCodeSelectionPass is mandatory, depends on CallGraphAnalysis, and implements the following transform:
- Traverse the call-graph, and check for functions that are roots for accelerator execution (at the moment, these are GPU kernels exclusively, and would originate in the accelerator specific algorithm library the toolchain uses as an implementation detail);
- Starting from a root, do a BFS to find all functions that are reachable (called directly or indirectly via a call- chain) and record them;
- After having done the above for all roots in the Module, we have the computed the set of reachable functions, which is the union of roots and functions reachable from roots;
- All functions that are not in the reachable set are removed; for the special case where the reachable set is empty we completely clear the module;
2. HipStdParAllocationInterpositionPass is optional, is meant as a fallback with restricted functionality for cases where on-demand paging is unavailable on a platform, and implements the following transform:
- Iterate all functions in a Module;
- If a function's name is in a predefined set of allocation / deallocation that the runtime implementation is allowed and expected to interpose, replace all its uses with the equivalent accelerator aware function, iff the latter is available;
- If the accelerator aware equivalent is unavailable we warn, but compilation will go ahead, which means that it is possible to get issues around the accelerator trying to access inaccessible memory at run time;
- We rely on direct name matching as opposed to using the new alloc-kind family of attributes and / or the LibCall analysis pass because some of the legacy functions that need replacing would not carry the former or be identified by the latter.
Reviewed by: JonChesterfield, yaxunl
Differential Revision: https://reviews.llvm.org/D155856
This patch adds the LLVM changes needed for enabling HIP parallel algorithm offload on AMDGPU targets. What we do here is add two passes, one mandatory and one optional:
1. HipStdParAcceleratorCodeSelectionPass is mandatory, depends on CallGraphAnalysis, and implements the following transform:
- Traverse the call-graph, and check for functions that are roots for accelerator execution (at the moment, these are GPU kernels exclusively, and would originate in the accelerator specific algorithm library the toolchain uses as an implementation detail);
- Starting from a root, do a BFS to find all functions that are reachable (called directly or indirectly via a call- chain) and record them;
- After having done the above for all roots in the Module, we have the computed the set of reachable functions, which is the union of roots and functions reachable from roots;
- All functions that are not in the reachable set are removed; for the special case where the reachable set is empty we completely clear the module;
2. HipStdParAllocationInterpositionPass is optional, is meant as a fallback with restricted functionality for cases where on-demand paging is unavailable on a platform, and implements the following transform:
- Iterate all functions in a Module;
- If a function's name is in a predefined set of allocation / deallocation that the runtime implementation is allowed and expected to interpose, replace all its uses with the equivalent accelerator aware function, iff the latter is available;
- If the accelerator aware equivalent is unavailable we warn, but compilation will go ahead, which means that it is possible to get issues around the accelerator trying to access inaccessible memory at run time;
- We rely on direct name matching as opposed to using the new alloc-kind family of attributes and / or the LibCall analysis pass because some of the legacy functions that need replacing would not carry the former or be identified by the latter.
Reviewed by: JonChesterfield, yaxunl
Differential Revision: https://reviews.llvm.org/D155856
This patch adds the LLVM changes needed for enabling HIP parallel algorithm offload on AMDGPU targets. What we do here is add two passes, one mandatory and one optional:
1. HipStdParAcceleratorCodeSelectionPass is mandatory, depends on CallGraphAnalysis, and implements the following transform:
- Traverse the call-graph, and check for functions that are roots for accelerator execution (at the moment, these are GPU kernels exclusively, and would originate in the accelerator specific algorithm library the toolchain uses as an implementation detail);
- Starting from a root, do a BFS to find all functions that are reachable (called directly or indirectly via a call- chain) and record them;
- After having done the above for all roots in the Module, we have the computed the set of reachable functions, which is the union of roots and functions reachable from roots;
- All functions that are not in the reachable set are removed; for the special case where the reachable set is empty we completely clear the module;
2. HipStdParAllocationInterpositionPass is optional, is meant as a fallback with restricted functionality for cases where on-demand paging is unavailable on a platform, and implements the following transform:
- Iterate all functions in a Module;
- If a function's name is in a predefined set of allocation / deallocation that the runtime implementation is allowed and expected to interpose, replace all its uses with the equivalent accelerator aware function, iff the latter is available;
- If the accelerator aware equivalent is unavailable we warn, but compilation will go ahead, which means that it is possible to get issues around the accelerator trying to access inaccessible memory at run time;
- We rely on direct name matching as opposed to using the new alloc-kind family of attributes and / or the LibCall analysis pass because some of the legacy functions that need replacing would not carry the former or be identified by the latter.
Reviewed by: JonChesterfield, yaxunl
Differential Revision: https://reviews.llvm.org/D155856
User only can use opt to test LoopVersioningLICM pass, and this PR add
the option back(deleted in https://reviews.llvm.org/D137915) so that
it's easy for verifying if it is useful for some benchmarks.
Adjust the pipeline slightly to move ConstraintElim just before the loop
simplification pipeline. This increases the number of cases where SCEV
should can preserved in the future.
This also enables slightly more opportunities, by benefiting from
earlier CFG simplifications, which allow more conditions to be added.
Reviewed By: nikic, antoniofrighetto
Differential Revision: https://reviews.llvm.org/D158843
This pass aims to infer alignment for instructions as a separate pass,
to reduce redundant work done by InstCombine running multiple times. It
runs late in the pipeline, just before the back-end passes where this
information is most useful.
Differential Revision: https://reviews.llvm.org/D158529
Currently, the `-fprofile-udpate` is ignored when `-fprofile-generate` is in effect. This patch enables `-fprofile-update` for `-fprofile-generate`. This patch continues the work from https://reviews.llvm.org/D87737, which added `-fprofile-update` in the first place.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D157280
This reverts commit 1f37088679a5c2416707d477093950e48148d430 as it causes a
large regression in x264, and some other regressions in downstream embedded
benchmarks under LTO.
We currently only enable hoisting in the last SimplifyCFG run of
the function simplification pipeline. In particular this happens
after GVN, which means that instructions that were identical (and
thus hoistable) prior to GVN might no longer be so after it ran,
due to equality replacements (see the phase ordering test).
The history here is that D84108 restricted hoisting to the very
late (module optimization) pipeline only. Then D101468 went back
on that, and also performed it at the end of function simplification.
This patch goes one step further and allows it prior to GVN.
Importantly, we still don't perform hoisting before LoopRotate,
which was the original motivation for delaying it.
Differential Revision: https://reviews.llvm.org/D156532
This restores commit b4a82b62258c5f650a1cccf5b179933e6bae4867, reverted
in 3ab7ef28eebf9019eb3d3c4efd7ebfd160106bb1 because it was thought to
cause a bot failure, which ended up being unrelated to this patch set.
Differential Revision: https://reviews.llvm.org/D154856
Previously the MemProf profile was expected to be in the same profile
file as a normal PGO profile, passed via the usual -fprofile-use=
option, and was matched in the same pass. To simplify profile
preparation, since the raw MemProf profile requires the binary for
symbolization and may be simpler to index separately from the raw PGO
profile, and also to enable providing a MemProf profile for a SamplePGO
build, separate out the MemProf feedback option and matching pass.
This patch adds the -fmemory-profile-use=${file} option, and the
provided file is passed down to LLVM and ultimately used in a new
MemProfUsePass which performs the matching of just the memory profile
contents of that file.
Note that a single profile file containing both normal PGO and MemProf
profile data is still supported, and the relevant profile data is
matched by the appropriate matching pass(es) based on which option(s)
the profile is provided with (the same profile file can be supplied to
both feedback options).
Differential Revision: https://reviews.llvm.org/D154856
In the LTO pipeline we run InstCombine after LICM, which is
different to what we normally do without LTO. This has the
effect of undoing all the great work done by LICM to reduce
the cost of the loop when it hoists the fdiv out and replaces
it with fmul. When InstCombine runs after LICM it puts the
fdiv straight back which, on AArch64 at least, is darn
expensive. You can observe this problem in the SPEC2017
benchmark parest if you build with "-Ofast -flto" and the
loop-vectoriser uses an unroll factor of 1, which is what
often happens when tail-folding is enabled.
This is also a problem for scalar loops, or indeed any loop
where there is only one use of the preheader fdiv result in
the loop.
See InstCombinerImpl::visitFMul for the code that sinks the fdiv.
I've attempted to fix this by adding another LICM pass for Full
LTO after InstCombine. The alternative is to stop InstCombine
from sinking the fdiv into loops. See D87479 for a previous
discussion on this issue.
Differential Revision: https://reviews.llvm.org/D143631
Here's a high level summary of the changes in this patch. For more
information on rational, see the RFC.
(https://discourse.llvm.org/t/rfc-a-unified-lto-bitcode-frontend/61774).
- Add config parameter to LTO backend, specifying which LTO mode is
desired when using unified LTO.
- Add unified LTO flag to the summary index for efficiency. Unified
LTO modules can be detected without parsing the module.
- Make sure that the ModuleID is generated by incorporating more types
of symbols.
Differential Revision: https://reviews.llvm.org/D123803
Fat LTO objects contain both LTO compatible IR, as well as generated
object code. This allows users to defer the choice of whether to use LTO
or not to link-time. This is a feature available in GCC for some time,
and makes the existing -ffat-lto-objects flag functional in the same
way as GCC's.
Within LLVM, we add a new EmbedBitcodePass that serializes the module to
the object file, and expose a new pass pipeline for compiling fat
objects. The new pipeline initially clones the module and runs the
selected (Thin)LTOPrelink pipeline, after which it will serialize the
module into a `.llvm.lto` section of an ELF file. When compiling for
(Thin)LTO, this normally the point at which the compiler would emit a
object file containing the bitcode and metadata.
After that point we compile the original module using the
PerModuleDefaultPipeline used for non-LTO compilation. We generate
standard object files at the end of this pipeline, which contain machine
code and the new `.llvm.lto` section containing bitcode.
Since the two pipelines operate on different copies of the module, we
can be sure that the bitcode in the `.llvm.lto` section and object code
in `.text` are congruent with the existing output produced by the
default and LTO pipelines.
Original RFC: https://discourse.llvm.org/t/rfc-ffat-lto-objects-support/63977
Earlier versions of this patch were missing REQUIRES lines for llc
related tests in Transforms/EmbedBitcode. Those tests are now under
CodeGen/X86, which should avoid running the check on unsupported
platforms.
The EmbedbBitcodePass also returned PreservedAnalyses::all when adding a
metadata section, which failed expensive checks, since it modified the
module. This is now corrected.
Reviewed By: tejohnson, MaskRay, nikic
Differential Revision: https://reviews.llvm.org/D146776
D63932 added a module flag to indicate that we are executing the regular
LTO post merge pipeline, so that GlobalDCE could perform more aggressive
optimization for Dead Virtual Function Elimination. This caused issues
trying to reuse bitcode that had already been through the LTO pipeline
(see context in D139816).
Instead support this by passing down a parameter flag to the
GlobalDCEPass constructor, which is the more usual way for indicating
this information.
Most test changes are to remove incidental uses of this flag. Of the 2
real uses, llvm/test/LTO/ARM/lto-linking-metadata.ll is now obsolete and
removed in this patch, and the virtual-functions-visibility-post-lto.ll
test is updated to use the regular LTO default pipeline where this
parameter is set to true.
Differential Revision: https://reviews.llvm.org/D153655
Fat LTO objects contain both LTO compatible IR, as well as generated
object code. This allows users to defer the choice of whether to use LTO
or not to link-time. This is a feature available in GCC for some time,
and makes the existing -ffat-lto-objects flag functional in the same
way as GCC's.
Within LLVM, we add a new EmbedBitcodePass that serializes the module to
the object file, and expose a new pass pipeline for compiling fat
objects. The new pipeline initially clones the module and runs the
selected (Thin)LTOPrelink pipeline, after which it will serialize the
module into a `.llvm.lto` section of an ELF file. When compiling for
(Thin)LTO, this normally the point at which the compiler would emit a
object file containing the bitcode and metadata.
After that point we compile the original module using the
PerModuleDefaultPipeline used for non-LTO compilation. We generate
standard object files at the end of this pipeline, which contain machine
code and the new `.llvm.lto` section containing bitcode.
Since the two pipelines operate on different copies of the module, we
can be sure that the bitcode in the `.llvm.lto` section and object code
in `.text` are congruent with the existing output produced by the
default and LTO pipelines.
Original RFC: https://discourse.llvm.org/t/rfc-ffat-lto-objects-support/63977
Earlier versions of this patch were missing REQUIRES lines for llc
related tests in Transforms/EmbedBitcode. Those tests are now under
CodeGen/X86, which should avoid running the check on unsupported
platforms.
Reviewed By: tejohnson, MaskRay, nikic
Differential Revision: https://reviews.llvm.org/D146776
There seems to be a problem on arm buildbots. Reverting until I can
investigate. https://lab.llvm.org/buildbot#builders/245/builds/10184
This reverts commit a67208e1c697649ce432e6497f56a93675273dd8
and dependent commit e54a3112cee5ae0a9117359ecbea878e1388f51e.
Fat LTO objects contain both LTO compatible IR, as well as generated
object code. This allows users to defer the choice of whether to use LTO
or not to link-time. This is a feature available in GCC for some time,
and makes the existing -ffat-lto-objects flag functional in the same
way as GCC's.
Within LLVM, we add a new EmbedBitcodePass that serializes the module to
the object file, and expose a new pass pipeline for compiling fat
objects. The new pipeline initially clones the module and runs the
selected (Thin)LTOPrelink pipeline, after which it will serialize the
module into a `.llvm.lto` section of an ELF file. When compiling for
(Thin)LTO, this normally the point at which the compiler would emit a
object file containing the bitcode and metadata.
After that point we compile the original module using the
PerModuleDefaultPipeline used for non-LTO compilation. We generate
standard object files at the end of this pipeline, which contain machine
code and the new `.llvm.lto` section containing bitcode.
Since the two pipelines operate on different copies of the module, we
can be sure that the bitcode in the `.llvm.lto` section and object code
in `.text` are congruent with the existing output produced by the
default and LTO pipelines.
Original RFC: https://discourse.llvm.org/t/rfc-ffat-lto-objects-support/63977
Reviewed By: tejohnson, MaskRay, nikic
Differential Revision: https://reviews.llvm.org/D146776
First, removes the invocation of the memprof instrumentation passes from
the end of the module simplification pass builder, where it doesn't
really belong. However, it turns out that this was never being invoked,
as it is guarded by an internal option not used anywhere (even tests).
These passes are actually added via clang under the -fmemory-profile
option. Changed this to add via the EP callback interface, similar to
the sanitizer passes. They are added to the EP for the end of the
optimization pipeline, which is roughly where they were being added
already (end of the pre-LTO link pipelines and non-LTO optimization
pipeline).
Ideally we should plumb the output file through to LLVM and set it up
there, so I have added a TODO.
Differential Revision: https://reviews.llvm.org/D151593
GlobalDCE will only remove functions with available externally
linkage if they are unreferenced. As such, I don't believe there
is any problem with running this pass as part of the ThinLTO pre-link
pipeline. It will only remove functions that are completely dead in
that module, and I don't think there is any benefit to keeping them
around for the post-link phase.
There is no compile-time impact from the additional pass.
This is a followup to one of the side discussions in D146776.
Differential Revision: https://reviews.llvm.org/D149446
Applies ThinLTO cloning decisions made during the thin link and
recorded in the summary index to the IR during the ThinLTO backend.
Depends on D141077.
Differential Revision: https://reviews.llvm.org/D149117
This reverts commit 6f29d1adf29820daae9ea7a01ae2588b67735b9e.
https://reviews.llvm.org/D149768 is causing size regressions for -Oz
with FullLTO, and I'm reverting that one while investigating. This
commit depends on that one, so it needs to be reverted as well.
This is a cheap pass so there's no need to limit to -O3.
This removes some differences between various pipelines.
Code size regressions should be addressed with
https://reviews.llvm.org/D149768.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D148269
