| Commit message (Collapse) | Author | Age | Files | Lines |
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Summary:
An assert added to the index-based WPD was trying to verify that we only
have multiple vtables for a given guid when they are all non-external
linkage. This is too conservative because we may have multiple external
vtable with the same guid when they are in comdat. Remove the assert,
as we don't have comdat information in the index, the linker should
issue an error in this case.
See discussion on D71040 for more information.
Reviewers: evgeny777, aganea
Subscribers: mehdi_amini, inglorion, hiraditya, steven_wu, dexonsmith, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D72648
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Summary:
Ensure that we can internalize values produced from two rounds of
promotion.
Note that this cannot happen currently via clang, but in other use cases
such as the Rust compiler which does a first round of ThinLTO on library
code, producing bitcode, and a second round on the final binary.
In particular this can happen if a function is exported and promoted,
ending up with a ".llvm.${hash}" suffix, and then goes through a round
of optimization creating an internal switch table expansion variable
that is internal and contains the promoted name of the enclosing
function. This variable will be promoted in the second round of ThinLTO
if @foo is imported again, and therefore ends up with two
".llvm.${hash}" suffixes. Only the final one should be stripped when
consulting the index to locate the summary.
Reviewers: wmi
Subscribers: mehdi_amini, inglorion, hiraditya, JDevlieghere, steven_wu, dexonsmith, arphaman, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D72711
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Summary:
A recent fix in D69452 fixed index based WPD in the presence of
available_externally vtables. It added a cast of the vtable def
summary to a GlobalVarSummary. However, in some cases one def may be an
alias, in which case we need to get the base object before casting,
otherwise we will crash.
Reviewers: evgeny777, steven_wu, aganea
Subscribers: mehdi_amini, inglorion, hiraditya, dexonsmith, arphaman, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D71040
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Summary: The specific number of records loaded depends on the number of kinds, but the difference between the lazy and not lazy cases does not.
Reviewers: modocache
Subscribers: llvm-commits, dexonsmith, steven_wu, hiraditya, mehdi_amini
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D71882
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kinds"
This reverts commit be4704bd41a4dd8bb5c4dd5a614744c69fb3cf8e.
This test fails on Windows without awk.
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Summary: The specific number of records loaded depends on the number of kinds, but the difference between the lazy and not lazy cases does not.
Reviewers: modocache
Subscribers: llvm-commits, dexonsmith, steven_wu, hiraditya, mehdi_amini
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D71882
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kinds"
This reverts commit 2e6c15d1e7a47f11fab2dd3a40fcff01906923ae.
It causes the test to fail on Windows
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Summary: The specific number of records loaded depends on the number of kinds, but the difference between the lazy and not lazy cases does not.
Reviewers: modocache
Subscribers: mehdi_amini, hiraditya, steven_wu, dexonsmith, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D71730
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Differential revision: https://reviews.llvm.org/D71608
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Summary:
Add an option to allow the attribute propagation on the index to be
disabled, to allow a workaround for issues (such as that fixed by
D70977).
Also move the setting of the WithAttributePropagation flag on the index
into propagateAttributes(), and remove some old stale code that predated
this flag and cleared the maybe read/write only bits when we need to
disable the propagation (previously only when importing disabled, now
also when the new option disables it).
Reviewers: evgeny777, steven_wu
Subscribers: mehdi_amini, inglorion, hiraditya, dexonsmith, arphaman, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D70984
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Summary:
D69561/dde5893 enabled importing of readonly variables with references,
however, it introduced a bug relating to importing/internalization of
writeonly variables with references.
A fix for this was added in D70006/7f92d66. But this didn't work in
distributed ThinLTO mode. The reason is that the fix (importing the
writeonly var with a zeroinitializer) was only applied when there were
references on the writeonly var summary. In distributed ThinLTO mode,
where we only have a small slice of the index, we will not have the
references on the importing side if we are not importing those
referenced values. Rather than changing this handshaking (which will
require a lot of other changes, since that's how we know what to import
in the distributed backend clang invocation), we can simply always give
the writeonly variable a zero initializer.
Reviewers: evgeny777, steven_wu
Subscribers: mehdi_amini, inglorion, hiraditya, dexonsmith, arphaman, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D70977
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Since we now have multiple formats, the ThinLTO remark files should also
respect that.
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Differential revision: https://reviews.llvm.org/D70383
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Summary: The earlier commit (https://reviews.llvm.org/D70014) missed this one : If Always_Inline happens to be the only entry in FuncFlags, then the assembler will not print it in the summary.
Patch by Bharathi Seshadri <bseshadr@cisco.com>
Reviewers: tejohnson
Reviewed By: tejohnson
Subscribers: mehdi_amini, inglorion, hiraditya, steven_wu, dexonsmith, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D70323
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Summary: A user can force a function to be inlined by specifying the always_inline attribute. Currently, thinlto implementation is not aware of always_inline functions and does not guarantee import of such functions, which in turn can prevent inlining of such functions.
Patch by Bharathi Seshadri <bseshadr@cisco.com>
Reviewers: tejohnson
Reviewed By: tejohnson
Subscribers: mehdi_amini, inglorion, hiraditya, steven_wu, dexonsmith, arphaman, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D70014
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Patch enables import of write-only variables with non-trivial initializers
to fix linker errors. Initializers of imported variables are converted to
'zeroinitializer' to avoid promotion of referenced objects.
Differential revision: https://reviews.llvm.org/D70006
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Patch allows importing declarations of functions and variables, referenced
by the initializer of some other readonly variable.
Differential revision: https://reviews.llvm.org/D69561
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This recommits cc0b9647b76178bc3869bbfff80535ad86366472 which was
reverted in d39d1a2f87aca3cfabe58ecfa5146879baa70096.
I added a fix for an issue found when testing via distributed ThinLTO,
and added a test case for that failure.
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This reverts commit cc0b9647b76178bc3869bbfff80535ad86366472.
The commit is causing a failure in internal testing. Will recommit with
a fix later.
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Summary:
Clang does not add type metadata to available_externally vtables. When
choosing a summary to look at for virtual function definitions, make
sure we skip summaries for any available externally vtables as they will
not describe any virtual function functions, which are only summarized
in the presence of type metadata on the vtable def. Simply look for the
corresponding strong def's summary.
Also add handling for same-named local vtables with the same GUID
because of same-named files without enough distinguishing path.
In that case we return a conservative result with no devirtualization.
Reviewers: pcc, davidxl, evgeny777
Subscribers: mehdi_amini, inglorion, hiraditya, steven_wu, dexonsmith, arphaman, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D69452
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Summary:
If there are a GUID collision between two globals checking the
summarylist from the import index to make assumption can be dangerous.
Do not assume that a GlobalValue that has a GlobalVarSummary
actually is a GlobalVariable as it can be another GlobalValue with
the same GUID that the summary is connected to.
Patch by Joel Klinghed (the_jk@opera.com)
Reviewers: evgeny777, tejohnson
Reviewed By: tejohnson
Subscribers: tejohnson, dblaikie, MaskRay, mehdi_amini, inglorion, hiraditya, steven_wu, dexonsmith, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D67322
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Differential revision: https://reviews.llvm.org/D69107
llvm-svn: 375493
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PS4 buildbot seems to be dropping variable names for some reason
llvm-svn: 375237
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llvm-svn: 375235
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Differential revision: https://reviews.llvm.org/D68950
llvm-svn: 375219
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Remove dead virtual functions from vtables with
replaceNonMetadataUsesWith, so that CGProfile metadata gets cleaned up
correctly.
Original commit message:
Currently, it is hard for the compiler to remove unused C++ virtual
functions, because they are all referenced from vtables, which are referenced
by constructors. This means that if the constructor is called from any live
code, then we keep every virtual function in the final link, even if there
are no call sites which can use it.
This patch allows unused virtual functions to be removed during LTO (and
regular compilation in limited circumstances) by using type metadata to match
virtual function call sites to the vtable slots they might load from. This
information can then be used in the global dead code elimination pass instead
of the references from vtables to virtual functions, to more accurately
determine which functions are reachable.
To make this transformation safe, I have changed clang's code-generation to
always load virtual function pointers using the llvm.type.checked.load
intrinsic, instead of regular load instructions. I originally tried writing
this using clang's existing code-generation, which uses the llvm.type.test
and llvm.assume intrinsics after doing a normal load. However, it is possible
for optimisations to obscure the relationship between the GEP, load and
llvm.type.test, causing GlobalDCE to fail to find virtual function call
sites.
The existing linkage and visibility types don't accurately describe the scope
in which a virtual call could be made which uses a given vtable. This is
wider than the visibility of the type itself, because a virtual function call
could be made using a more-visible base class. I've added a new
!vcall_visibility metadata type to represent this, described in
TypeMetadata.rst. The internalization pass and libLTO have been updated to
change this metadata when linking is performed.
This doesn't currently work with ThinLTO, because it needs to see every call
to llvm.type.checked.load in the linkage unit. It might be possible to
extend this optimisation to be able to use the ThinLTO summary, as was done
for devirtualization, but until then that combination is rejected in the
clang driver.
To test this, I've written a fuzzer which generates random C++ programs with
complex class inheritance graphs, and virtual functions called through object
and function pointers of different types. The programs are spread across
multiple translation units and DSOs to test the different visibility
restrictions.
I've also tried doing bootstrap builds of LLVM to test this. This isn't
ideal, because only classes in anonymous namespaces can be optimised with
-fvisibility=default, and some parts of LLVM (plugins and bugpoint) do not
work correctly with -fvisibility=hidden. However, there are only 12 test
failures when building with -fvisibility=hidden (and an unmodified compiler),
and this change does not cause any new failures for either value of
-fvisibility.
On the 7 C++ sub-benchmarks of SPEC2006, this gives a geomean code-size
reduction of ~6%, over a baseline compiled with "-O2 -flto
-fvisibility=hidden -fwhole-program-vtables". The best cases are reductions
of ~14% in 450.soplex and 483.xalancbmk, and there are no code size
increases.
I've also run this on a set of 8 mbed-os examples compiled for Armv7M, which
show a geomean size reduction of ~3%, again with no size increases.
I had hoped that this would have no effect on performance, which would allow
it to awlays be enabled (when using -fwhole-program-vtables). However, the
changes in clang to use the llvm.type.checked.load intrinsic are causing ~1%
performance regression in the C++ parts of SPEC2006. It should be possible to
recover some of this perf loss by teaching optimisations about the
llvm.type.checked.load intrinsic, which would make it worth turning this on
by default (though it's still dependent on -fwhole-program-vtables).
Differential revision: https://reviews.llvm.org/D63932
llvm-svn: 375094
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Differential revision: https://reviews.llvm.org/D68782
llvm-svn: 375083
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This reverts commit 9f6a873268e1ad9855873d9d8007086c0d01cf4f.
llvm-svn: 374844
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Currently, it is hard for the compiler to remove unused C++ virtual
functions, because they are all referenced from vtables, which are referenced
by constructors. This means that if the constructor is called from any live
code, then we keep every virtual function in the final link, even if there
are no call sites which can use it.
This patch allows unused virtual functions to be removed during LTO (and
regular compilation in limited circumstances) by using type metadata to match
virtual function call sites to the vtable slots they might load from. This
information can then be used in the global dead code elimination pass instead
of the references from vtables to virtual functions, to more accurately
determine which functions are reachable.
To make this transformation safe, I have changed clang's code-generation to
always load virtual function pointers using the llvm.type.checked.load
intrinsic, instead of regular load instructions. I originally tried writing
this using clang's existing code-generation, which uses the llvm.type.test
and llvm.assume intrinsics after doing a normal load. However, it is possible
for optimisations to obscure the relationship between the GEP, load and
llvm.type.test, causing GlobalDCE to fail to find virtual function call
sites.
The existing linkage and visibility types don't accurately describe the scope
in which a virtual call could be made which uses a given vtable. This is
wider than the visibility of the type itself, because a virtual function call
could be made using a more-visible base class. I've added a new
!vcall_visibility metadata type to represent this, described in
TypeMetadata.rst. The internalization pass and libLTO have been updated to
change this metadata when linking is performed.
This doesn't currently work with ThinLTO, because it needs to see every call
to llvm.type.checked.load in the linkage unit. It might be possible to
extend this optimisation to be able to use the ThinLTO summary, as was done
for devirtualization, but until then that combination is rejected in the
clang driver.
To test this, I've written a fuzzer which generates random C++ programs with
complex class inheritance graphs, and virtual functions called through object
and function pointers of different types. The programs are spread across
multiple translation units and DSOs to test the different visibility
restrictions.
I've also tried doing bootstrap builds of LLVM to test this. This isn't
ideal, because only classes in anonymous namespaces can be optimised with
-fvisibility=default, and some parts of LLVM (plugins and bugpoint) do not
work correctly with -fvisibility=hidden. However, there are only 12 test
failures when building with -fvisibility=hidden (and an unmodified compiler),
and this change does not cause any new failures for either value of
-fvisibility.
On the 7 C++ sub-benchmarks of SPEC2006, this gives a geomean code-size
reduction of ~6%, over a baseline compiled with "-O2 -flto
-fvisibility=hidden -fwhole-program-vtables". The best cases are reductions
of ~14% in 450.soplex and 483.xalancbmk, and there are no code size
increases.
I've also run this on a set of 8 mbed-os examples compiled for Armv7M, which
show a geomean size reduction of ~3%, again with no size increases.
I had hoped that this would have no effect on performance, which would allow
it to awlays be enabled (when using -fwhole-program-vtables). However, the
changes in clang to use the llvm.type.checked.load intrinsic are causing ~1%
performance regression in the C++ parts of SPEC2006. It should be possible to
recover some of this perf loss by teaching optimisations about the
llvm.type.checked.load intrinsic, which would make it worth turning this on
by default (though it's still dependent on -fwhole-program-vtables).
Differential revision: https://reviews.llvm.org/D63932
llvm-svn: 374539
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Summary:
This fixes a hole in the handling of devirtualized targets that were
local but need promoting due to devirtualization in another module. We
were not correctly referencing the promoted symbol in some cases. Make
sure the code that updates the name also looks at the ExportedGUIDs set
by utilizing a callback that checks all conditions (the callback
utilized by the internalization/promotion code).
Reviewers: pcc, davidxl, hiraditya
Subscribers: mehdi_amini, Prazek, inglorion, steven_wu, dexonsmith, dang, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D68159
llvm-svn: 373485
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Annotations in LLVM"
This patch contains the basic functionality for reporting potentially
incorrect usage of __builtin_expect() by comparing the developer's
annotation against a collected PGO profile. A more detailed proposal and
discussion appears on the CFE-dev mailing list
(http://lists.llvm.org/pipermail/cfe-dev/2019-July/062971.html) and a
prototype of the initial frontend changes appear here in D65300
We revised the work in D65300 by moving the misexpect check into the
LLVM backend, and adding support for IR and sampling based profiles, in
addition to frontend instrumentation.
We add new misexpect metadata tags to those instructions directly
influenced by the llvm.expect intrinsic (branch, switch, and select)
when lowering the intrinsics. The misexpect metadata contains
information about the expected target of the intrinsic so that we can
check against the correct PGO counter when emitting diagnostics, and the
compiler's values for the LikelyBranchWeight and UnlikelyBranchWeight.
We use these branch weight values to determine when to emit the
diagnostic to the user.
A future patch should address the comment at the top of
LowerExpectIntrisic.cpp to hoist the LikelyBranchWeight and
UnlikelyBranchWeight values into a shared space that can be accessed
outside of the LowerExpectIntrinsic pass. Once that is done, the
misexpect metadata can be updated to be smaller.
In the long term, it is possible to reconstruct portions of the
misexpect metadata from the existing profile data. However, we have
avoided this to keep the code simple, and because some kind of metadata
tag will be required to identify which branch/switch/select instructions
are influenced by the use of llvm.expect
Patch By: paulkirth
Differential Revision: https://reviews.llvm.org/D66324
llvm-svn: 371635
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Annotations in LLVM"
This reverts commit r371584. It introduced a dependency from compiler-rt
to llvm/include/ADT, which is problematic for multiple reasons.
One is that it is a novel dependency edge, which needs cross-compliation
machinery for llvm/include/ADT (yes, it is true that right now
compiler-rt included only header-only libraries, however, if we allow
compiler-rt to depend on anything from ADT, other libraries will
eventually get used).
Secondly, depending on ADT from compiler-rt exposes ADT symbols from
compiler-rt, which would cause ODR violations when Clang is built with
the profile library.
llvm-svn: 371598
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This patch contains the basic functionality for reporting potentially
incorrect usage of __builtin_expect() by comparing the developer's
annotation against a collected PGO profile. A more detailed proposal and
discussion appears on the CFE-dev mailing list
(http://lists.llvm.org/pipermail/cfe-dev/2019-July/062971.html) and a
prototype of the initial frontend changes appear here in D65300
We revised the work in D65300 by moving the misexpect check into the
LLVM backend, and adding support for IR and sampling based profiles, in
addition to frontend instrumentation.
We add new misexpect metadata tags to those instructions directly
influenced by the llvm.expect intrinsic (branch, switch, and select)
when lowering the intrinsics. The misexpect metadata contains
information about the expected target of the intrinsic so that we can
check against the correct PGO counter when emitting diagnostics, and the
compiler's values for the LikelyBranchWeight and UnlikelyBranchWeight.
We use these branch weight values to determine when to emit the
diagnostic to the user.
A future patch should address the comment at the top of
LowerExpectIntrisic.cpp to hoist the LikelyBranchWeight and
UnlikelyBranchWeight values into a shared space that can be accessed
outside of the LowerExpectIntrinsic pass. Once that is done, the
misexpect metadata can be updated to be smaller.
In the long term, it is possible to reconstruct portions of the
misexpect metadata from the existing profile data. However, we have
avoided this to keep the code simple, and because some kind of metadata
tag will be required to identify which branch/switch/select instructions
are influenced by the use of llvm.expect
Patch By: paulkirth
Differential Revision: https://reviews.llvm.org/D66324
llvm-svn: 371584
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for 32 bit signed, 32 bit unsigned, and 64 bit pointers."
This reverts 57076d3199fc2b0af4a3736b7749dd5462cacda5.
Original review at https://reviews.llvm.org/D64931.
Review for added fix at https://reviews.llvm.org/D66843.
llvm-svn: 371568
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Annotations in LLVM"
This reverts commit r371484: this broke sanitizer-x86_64-linux-fast bot.
llvm-svn: 371488
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This patch contains the basic functionality for reporting potentially
incorrect usage of __builtin_expect() by comparing the developer's
annotation against a collected PGO profile. A more detailed proposal and
discussion appears on the CFE-dev mailing list
(http://lists.llvm.org/pipermail/cfe-dev/2019-July/062971.html) and a
prototype of the initial frontend changes appear here in D65300
We revised the work in D65300 by moving the misexpect check into the
LLVM backend, and adding support for IR and sampling based profiles, in
addition to frontend instrumentation.
We add new misexpect metadata tags to those instructions directly
influenced by the llvm.expect intrinsic (branch, switch, and select)
when lowering the intrinsics. The misexpect metadata contains
information about the expected target of the intrinsic so that we can
check against the correct PGO counter when emitting diagnostics, and the
compiler's values for the LikelyBranchWeight and UnlikelyBranchWeight.
We use these branch weight values to determine when to emit the
diagnostic to the user.
A future patch should address the comment at the top of
LowerExpectIntrisic.cpp to hoist the LikelyBranchWeight and
UnlikelyBranchWeight values into a shared space that can be accessed
outside of the LowerExpectIntrinsic pass. Once that is done, the
misexpect metadata can be updated to be smaller.
In the long term, it is possible to reconstruct portions of the
misexpect metadata from the existing profile data. However, we have
avoided this to keep the code simple, and because some kind of metadata
tag will be required to identify which branch/switch/select instructions
are influenced by the use of llvm.expect
Patch By: paulkirth
Differential Revision: https://reviews.llvm.org/D66324
llvm-svn: 371484
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commits
r370083 has been reverted, which this change depends on.
llvm-svn: 370147
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signed,"
This reverts commit r370083 because it caused check-lld failures on
sanitizer-x86_64-linux-fast.
llvm-svn: 370142
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llvm-svn: 370105
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32 bit unsigned, and 64 bit pointers.
llvm-svn: 370083
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Summary:
Keep aliasees alive if their alias is live, otherwise we end up with an
alias to a declaration, which is invalid. This can happen when the
aliasee is weak and non-prevailing.
This fix exposed the fact that we were then attempting to internalize
the weak symbol, which was not exported as it was not prevailing. We
should not internalize interposable symbols in general, unless this is
the prevailing copy, since it can lead to incorrect inlining and other
optimizations. Most of the changes in this patch are due to the
restructuring required to pass down the prevailing callback.
Finally, while implementing the test cases, I found that in the case of
a weak aliasee that is still marked not live because its alias isn't
live, after dropping the definition we incorrectly marked the
declaration with weak linkage when resolving prevailing symbols in the
module. This was due to some special case handling for symbols marked
WeakLinkage in the summary located before instead of after a subsequent
check for the symbol being a declaration. It turns out that we don't
actually need this special case handling any more (looking back at the
history, when that was added the code was structured quite differently)
- we will correctly mark with weak linkage further below when the
definition hasn't been dropped.
Fixes PR42542.
Reviewers: pcc
Subscribers: mehdi_amini, inglorion, steven_wu, dexonsmith, dang, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D66264
llvm-svn: 369766
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llvm-lto2 doesn't treat "-" as stdout, so the test added in r369024 creates a
file named "-.0". This patch makes the test look more like other tests that use
llvm-lto2.
llvm-svn: 369066
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Summary: IR printing has not been correctly supported with (Thin)LTO if the new pass manager is enabled. Previously we only get outputs from backend(codegen) passes, as they are still under legacy pass manager even when the new pass manager is enabled. This patch addresses the issue and enables IR printing for optimization passes with new pass manager + (Thin)LTO setting.
Reviewers: fedor.sergeev, philip.pfaffe
Subscribers: mehdi_amini, inglorion, hiraditya, steven_wu, dexonsmith, dang, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D66253
llvm-svn: 369024
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For consistency with normal instructions and clarity when reading IR,
it's best to print the %0, %1, ... names of function arguments in
definitions.
Also modifies the parser to accept IR in that form for obvious reasons.
llvm-svn: 367755
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New test added in r367679 used nm and should use llvm-nm.
llvm-svn: 367688
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Fix second (and last) instance of wrong Input file name in new test
added in r367679.
llvm-svn: 367682
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Thew new test added in r367679 was using the wrong copy of the Input
file.
llvm-svn: 367680
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This patch adds support to the WholeProgramDevirt pass to perform
index-based WPD, which is invoked from ThinLTO during the thin link.
The ThinLTO backend (WPD import phase) behaves the same regardless of
whether the WPD decisions were made with the index-based or (the
existing) IR-based analysis.
Depends on D54815.
Reviewers: pcc
Subscribers: mehdi_amini, inglorion, eraman, steven_wu, dexonsmith, arphaman, dang, llvm-commits
Differential Revision: https://reviews.llvm.org/D55153
llvm-svn: 367679
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Summary: We emit CFI_FUNCTION_DEFS and CFI_FUNCTION_DECLS to
distributed ThinLTO indices to implement indirect function call
checking. This change causes us to only emit entries for functions
that are either defined or used by the module we're writing the index
for (instead of all functions in the combined index), which can make
the indices substantially smaller.
Fixes PR42378.
Reviewers: pcc, vitalybuka, eugenis
Subscribers: mehdi_amini, hiraditya, dexonsmith, arphaman, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D63887
llvm-svn: 365537
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For background of BPF CO-RE project, please refer to
http://vger.kernel.org/bpfconf2019.html
In summary, BPF CO-RE intends to compile bpf programs
adjustable on struct/union layout change so the same
program can run on multiple kernels with adjustment
before loading based on native kernel structures.
In order to do this, we need keep track of GEP(getelementptr)
instruction base and result debuginfo types, so we
can adjust on the host based on kernel BTF info.
Capturing such information as an IR optimization is hard
as various optimization may have tweaked GEP and also
union is replaced by structure it is impossible to track
fieldindex for union member accesses.
Three intrinsic functions, preserve_{array,union,struct}_access_index,
are introducted.
addr = preserve_array_access_index(base, index, dimension)
addr = preserve_union_access_index(base, di_index)
addr = preserve_struct_access_index(base, gep_index, di_index)
here,
base: the base pointer for the array/union/struct access.
index: the last access index for array, the same for IR/DebugInfo layout.
dimension: the array dimension.
gep_index: the access index based on IR layout.
di_index: the access index based on user/debuginfo types.
For example, for the following example,
$ cat test.c
struct sk_buff {
int i;
int b1:1;
int b2:2;
union {
struct {
int o1;
int o2;
} o;
struct {
char flags;
char dev_id;
} dev;
int netid;
} u[10];
};
static int (*bpf_probe_read)(void *dst, int size, const void *unsafe_ptr)
= (void *) 4;
#define _(x) (__builtin_preserve_access_index(x))
int bpf_prog(struct sk_buff *ctx) {
char dev_id;
bpf_probe_read(&dev_id, sizeof(char), _(&ctx->u[5].dev.dev_id));
return dev_id;
}
$ clang -target bpf -O2 -g -emit-llvm -S -mllvm -print-before-all \
test.c >& log
The generated IR looks like below:
...
define dso_local i32 @bpf_prog(%struct.sk_buff*) #0 !dbg !15 {
%2 = alloca %struct.sk_buff*, align 8
%3 = alloca i8, align 1
store %struct.sk_buff* %0, %struct.sk_buff** %2, align 8, !tbaa !45
call void @llvm.dbg.declare(metadata %struct.sk_buff** %2, metadata !43, metadata !DIExpression()), !dbg !49
call void @llvm.lifetime.start.p0i8(i64 1, i8* %3) #4, !dbg !50
call void @llvm.dbg.declare(metadata i8* %3, metadata !44, metadata !DIExpression()), !dbg !51
%4 = load i32 (i8*, i32, i8*)*, i32 (i8*, i32, i8*)** @bpf_probe_read, align 8, !dbg !52, !tbaa !45
%5 = load %struct.sk_buff*, %struct.sk_buff** %2, align 8, !dbg !53, !tbaa !45
%6 = call [10 x %union.anon]* @llvm.preserve.struct.access.index.p0a10s_union.anons.p0s_struct.sk_buffs(
%struct.sk_buff* %5, i32 2, i32 3), !dbg !53, !llvm.preserve.access.index !19
%7 = call %union.anon* @llvm.preserve.array.access.index.p0s_union.anons.p0a10s_union.anons(
[10 x %union.anon]* %6, i32 1, i32 5), !dbg !53
%8 = call %union.anon* @llvm.preserve.union.access.index.p0s_union.anons.p0s_union.anons(
%union.anon* %7, i32 1), !dbg !53, !llvm.preserve.access.index !26
%9 = bitcast %union.anon* %8 to %struct.anon.0*, !dbg !53
%10 = call i8* @llvm.preserve.struct.access.index.p0i8.p0s_struct.anon.0s(
%struct.anon.0* %9, i32 1, i32 1), !dbg !53, !llvm.preserve.access.index !34
%11 = call i32 %4(i8* %3, i32 1, i8* %10), !dbg !52
%12 = load i8, i8* %3, align 1, !dbg !54, !tbaa !55
%13 = sext i8 %12 to i32, !dbg !54
call void @llvm.lifetime.end.p0i8(i64 1, i8* %3) #4, !dbg !56
ret i32 %13, !dbg !57
}
!19 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "sk_buff", file: !3, line: 1, size: 704, elements: !20)
!26 = distinct !DICompositeType(tag: DW_TAG_union_type, scope: !19, file: !3, line: 5, size: 64, elements: !27)
!34 = distinct !DICompositeType(tag: DW_TAG_structure_type, scope: !26, file: !3, line: 10, size: 16, elements: !35)
Note that @llvm.preserve.{struct,union}.access.index calls have metadata llvm.preserve.access.index
attached to instructions to provide struct/union debuginfo type information.
For &ctx->u[5].dev.dev_id,
. The "%6 = ..." represents struct member "u" with index 2 for IR layout and index 3 for DI layout.
. The "%7 = ..." represents array subscript "5".
. The "%8 = ..." represents union member "dev" with index 1 for DI layout.
. The "%10 = ..." represents struct member "dev_id" with index 1 for both IR and DI layout.
Basically, traversing the use-def chain recursively for the 3rd argument of bpf_probe_read() and
examining all preserve_*_access_index calls, the debuginfo struct/union/array access index
can be achieved.
The intrinsics also contain enough information to regenerate codes for IR layout.
For array and structure intrinsics, the proper GEP can be constructed.
For union intrinsics, replacing all uses of "addr" with "base" should be enough.
The test case ThinLTO/X86/lazyload_metadata.ll is adjusted to reflect the
new addition of the metadata.
Signed-off-by: Yonghong Song <yhs@fb.com>
Differential Revision: https://reviews.llvm.org/D61810
llvm-svn: 365423
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