Revision tags: llvmorg-18.1.6 |
|
#
1650f1b3 |
| 15-May-2024 |
Jay Foad <jay.foad@amd.com> |
Fix typo "indicies" (#92232)
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#
d71771dd |
| 06-May-2024 |
Jan Voung <jvoung@gmail.com> |
Revert "Reapply "Use an abbrev to reduce size of VALUE_GUID records in ThinLTO summaries" (#90610)" (#91194)
Reverts llvm/llvm-project#90692
Breaking PPC buildbots. The bots are not meant to test
Revert "Reapply "Use an abbrev to reduce size of VALUE_GUID records in ThinLTO summaries" (#90610)" (#91194)
Reverts llvm/llvm-project#90692
Breaking PPC buildbots. The bots are not meant to test LLD, but are
running a test that is using an old version of LLD without the change
(so is incompatible). Revert until a fix is found.
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Revision tags: llvmorg-18.1.5 |
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#
28869a70 |
| 01-May-2024 |
Jan Voung <jvoung@gmail.com> |
Reapply "Use an abbrev to reduce size of VALUE_GUID records in ThinLTO summaries" (#90610) (#90692)
This reverts commit 2aabfc811670beb843074c765c056fff4a7b443b.
Add fixes to LLD and Gold tests m
Reapply "Use an abbrev to reduce size of VALUE_GUID records in ThinLTO summaries" (#90610) (#90692)
This reverts commit 2aabfc811670beb843074c765c056fff4a7b443b.
Add fixes to LLD and Gold tests missed in original change.
Co-authored-by: Jan Voung <jvoung@google.com>
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#
2aabfc81 |
| 30-Apr-2024 |
Jan Voung <jvoung@gmail.com> |
Revert "Use an abbrev to reduce size of VALUE_GUID records in ThinLTO summaries" (#90610)
Reverts llvm/llvm-project#90497
Broke some LLD tests.
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#
adabdc12 |
| 30-Apr-2024 |
Jan Voung <jvoung@gmail.com> |
Use an abbrev to reduce size of VALUE_GUID records in ThinLTO summaries (#90497)
GUID often have content in the higher bits of a 64-bit entry so using
the unabbrev encoding is inefficient (lots of
Use an abbrev to reduce size of VALUE_GUID records in ThinLTO summaries (#90497)
GUID often have content in the higher bits of a 64-bit entry so using
the unabbrev encoding is inefficient (lots of VBR control bits).
Instead, use an abbrev with two 32-bit fixed width chunks.
The abbrev also helps encode the "count" in one place instead of
in every record.
Reduces size of distributed backend summary files by 8.7% in one
example app.
Co-authored-by: Jan Voung <jvoung@google.com>
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Revision tags: llvmorg-18.1.4 |
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#
dda73336 |
| 11-Apr-2024 |
Mingming Liu <mingmingl@google.com> |
[ThinLTO]Record import type in GlobalValueSummary::GVFlags (#87597)
The motivating use case is to support import the function declaration
across modules to construct call graph edges for indirect c
[ThinLTO]Record import type in GlobalValueSummary::GVFlags (#87597)
The motivating use case is to support import the function declaration
across modules to construct call graph edges for indirect calls [1]
when importing the function definition costs too much compile time
(e.g., the function is too large has no `noinline` attribute).
1. Currently, when the compiled IR module doesn't have a function
definition but its postlink combined summary contains the function
summary or a global alias summary with this function as aliasee, the
function definition will be imported from source module by IRMover. The
implementation is in FunctionImporter::importFunctions [2]
2. In order for FunctionImporter to import a declaration of a function,
both function summary and alias summary need to carry the def / decl
state. Specifically, all existing summary fields doesn't differ across
import modules, but the def / decl state of is decided by
`<ImportModule, Function>`.
This change encodes the def/decl state in `GlobalValueSummary::GVFlags`.
In the subsequent changes
1. The indexing step `computeImportForModule` [3]
will compute the set of definitions and the set of declarations for each
module, and passing on the information to bitcode writer.
2. Bitcode writer will look up the def/decl state and sets the state
when it writes out the flag value. This is demonstrated in
https://github.com/llvm/llvm-project/pull/87600
3. Function importer will read the def/decl state when reading the
combined summary to figure out two sets of global values, and IRMover
will be updated to import the declaration (aka linkGlobalValuePrototype [4])
into the destination module.
- The next change is https://github.com/llvm/llvm-project/pull/87600
[1] mentioned in rfc https://discourse.llvm.org/t/rfc-for-better-call-graph-sort-build-a-more-complete-call-graph-by-adding-more-indirect-call-edges/74029#support-cross-module-function-declaration-import-5
[2] https://github.com/llvm/llvm-project/blob/3b337242ee165554f0017b00671381ec5b1ba855/llvm/lib/Transforms/IPO/FunctionImport.cpp#L1608-L1764
[3] https://github.com/llvm/llvm-project/blob/3b337242ee165554f0017b00671381ec5b1ba855/llvm/lib/Transforms/IPO/FunctionImport.cpp#L856
[4] https://github.com/llvm/llvm-project/blob/3b337242ee165554f0017b00671381ec5b1ba855/llvm/lib/Linker/IRMover.cpp#L605
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Revision tags: llvmorg-18.1.3 |
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#
1e15371d |
| 01-Apr-2024 |
Mingming Liu <mingmingl@google.com> |
[ThinLTO][TypeProf] Implement vtable def import (#79381)
Add annotated vtable GUID as referenced variables in per function
summary, and update bitcode writer to create value-ids for these
referenc
[ThinLTO][TypeProf] Implement vtable def import (#79381)
Add annotated vtable GUID as referenced variables in per function
summary, and update bitcode writer to create value-ids for these
referenced vtables.
- This is the part3 of type profiling work, and described in the "Virtual Table Definition Import" [1] section of the
RFC.
[1] https://github.com/llvm/llvm-project/pull/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
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#
7d3924ce |
| 29-Mar-2024 |
elhewaty <mohamedatef1698@gmail.com> |
[IR] Add nowrap flags for trunc instruction (#85592)
This patch adds the nuw (no unsigned wrap) and nsw (no signed wrap)
poison-generating flags to the trunc instruction.
Discourse thread:
htt
[IR] Add nowrap flags for trunc instruction (#85592)
This patch adds the nuw (no unsigned wrap) and nsw (no signed wrap)
poison-generating flags to the trunc instruction.
Discourse thread:
https://discourse.llvm.org/t/rfc-add-nowrap-flags-to-trunc/77453
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#
75dfa58e |
| 20-Mar-2024 |
Stephen Tozer <stephen.tozer@sony.com> |
[RemoveDIs][NFC] Rename DPMarker->DbgMarker (#85931)
Another trivial rename patch, the last big one for now, which renamed
DPMarkers to DbgMarkers. This required the field `DbgMarker` in
`Instruct
[RemoveDIs][NFC] Rename DPMarker->DbgMarker (#85931)
Another trivial rename patch, the last big one for now, which renamed
DPMarkers to DbgMarkers. This required the field `DbgMarker` in
`Instruction` to be renamed to `DebugMarker` to avoid a clash, but
otherwise was a simple string substitution of `s/DPMarker/DbgMarker` and
a manual renaming of `DPM` to `DM` in the few places where that acronym
was used for debug markers.
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#
bdc77d1e |
| 20-Mar-2024 |
Stephen Tozer <stephen.tozer@sony.com> |
[RemoveDIs][NFC] Rename DPLabel->DbgLabelRecord (#85918)
This patch renames DPLabel to DbgLabelRecord, in accordance with the
ongoing DbgRecord rename. This rename was fairly trivial, since DPLabel
[RemoveDIs][NFC] Rename DPLabel->DbgLabelRecord (#85918)
This patch renames DPLabel to DbgLabelRecord, in accordance with the
ongoing DbgRecord rename. This rename was fairly trivial, since DPLabel
isn't as widely used as DPValue and has no real conflicts in either its
full or abbreviated name. As usual, the entire replacement was done
automatically, with `s/DPLabel/DbgLabelRecord/` and `s/DPL/DLR/`.
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#
0f46e31c |
| 20-Mar-2024 |
Nikita Popov <npopov@redhat.com> |
[IR] Change representation of getelementptr inrange (#84341)
As part of the migration to ptradd
(https://discourse.llvm.org/t/rfc-replacing-getelementptr-with-ptradd/68699),
we need to change the
[IR] Change representation of getelementptr inrange (#84341)
As part of the migration to ptradd
(https://discourse.llvm.org/t/rfc-replacing-getelementptr-with-ptradd/68699),
we need to change the representation of the `inrange` attribute, which
is used for vtable splitting.
Currently, inrange is specified as follows:
```
getelementptr inbounds ({ [4 x ptr], [4 x ptr] }, ptr @vt, i64 0, inrange i32 1, i64 2)
```
The `inrange` is placed on a GEP index, and all accesses must be "in
range" of that index. The new representation is as follows:
```
getelementptr inbounds inrange(-16, 16) ({ [4 x ptr], [4 x ptr] }, ptr @vt, i64 0, i32 1, i64 2)
```
This specifies which offsets are "in range" of the GEP result. The new
representation will continue working when canonicalizing to ptradd
representation:
```
getelementptr inbounds inrange(-16, 16) (i8, ptr @vt, i64 48)
```
The inrange offsets are relative to the return value of the GEP. An
alternative design could make them relative to the source pointer
instead. The result-relative format was chosen on the off-chance that we
want to extend support to non-constant GEPs in the future, in which case
this variant is more expressive.
This implementation "upgrades" the old inrange representation in bitcode
by simply dropping it. This is a very niche feature, and I don't think
trying to upgrade it is worthwhile. Let me know if you disagree.
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Revision tags: llvmorg-18.1.2 |
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#
ffd08c77 |
| 19-Mar-2024 |
Stephen Tozer <stephen.tozer@sony.com> |
[RemoveDIs][NFC] Rename DPValue -> DbgVariableRecord (#85216)
This is the major rename patch that prior patches have built towards.
The DPValue class is being renamed to DbgVariableRecord, which re
[RemoveDIs][NFC] Rename DPValue -> DbgVariableRecord (#85216)
This is the major rename patch that prior patches have built towards.
The DPValue class is being renamed to DbgVariableRecord, which reflects
the updated terminology for the "final" implementation of the RemoveDI
feature. This is a pure string substitution + clang-format patch. The
only manual component of this patch was determining where to perform
these string substitutions: `DPValue` and `DPV` are almost exclusively
used for DbgRecords, *except* for:
- llvm/lib/target, where 'DP' is used to mean double-precision, and so
appears as part of .td files and in variable names. NB: There is a
single existing use of `DPValue` here that refers to debug info, which
I've manually updated.
- llvm/tools/gold, where 'LDPV' is used as a prefix for symbol
visibility enums.
Outside of these places, I've applied several basic string
substitutions, with the intent that they only affect DbgRecord-related
identifiers; I've checked them as I went through to verify this, with
reasonable confidence that there are no unintended changes that slipped
through the cracks. The substitutions applied are all case-sensitive,
and are applied in the order shown:
```
DPValue -> DbgVariableRecord
DPVal -> DbgVarRec
DPV -> DVR
```
Following the previous rename patches, it should be the case that there
are no instances of any of these strings that are meant to refer to the
general case of DbgRecords, or anything other than the DPValue class.
The idea behind this patch is therefore that pure string substitution is
correct in all cases as long as these assumptions hold.
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#
924a1dce |
| 19-Mar-2024 |
Daniil Kovalev <dkovalev@accesssoftek.com> |
[Dwarf] Support `__ptrauth` qualifier in metadata nodes (#83862)
Reland #82363 after fixing build failure
https://lab.llvm.org/buildbot/#/builders/5/builds/41428.
Memory sanitizer detects usage
[Dwarf] Support `__ptrauth` qualifier in metadata nodes (#83862)
Reland #82363 after fixing build failure
https://lab.llvm.org/buildbot/#/builders/5/builds/41428.
Memory sanitizer detects usage of `RawData` union member which is not
filled directly. Instead, the code relies on filling `Data` union
member, which is a struct consisting of signing schema parameters.
According to https://en.cppreference.com/w/cpp/language/union, this is
UB:
"It is undefined behavior to read from the member of the union that
wasn't most recently written".
Instead of relying on compiler allowing us to do dirty things, do not
use union and only store `RawData`. Particular ptrauth parameters are
obtained on demand via bit operations.
Original PR description below.
Emit `__ptrauth`-qualified types as `DIDerivedType` metadata nodes in IR
with tag `DW_TAG_LLVM_ptrauth_type`, baseType referring to the type
which has the qualifier applied, and the following parameters
representing the signing schema:
- `ptrAuthKey` (integer)
- `ptrAuthIsAddressDiscriminated` (boolean)
- `ptrAuthExtraDiscriminator` (integer)
- `ptrAuthIsaPointer` (boolean)
- `ptrAuthAuthenticatesNullValues` (boolean)
Co-authored-by: Ahmed Bougacha <ahmed@bougacha.org>
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#
435d4c12 |
| 15-Mar-2024 |
Orlando Cazalet-Hyams <orlando.hyams@sony.com> |
Reapply [RemoveDIs] Read/write DbgRecords directly from/to bitcode (#83251)
Reaplying after revert in #85382 (861ebe6446296c96578807363aa292c69d827773). Fixed intermittent test failure by avoiding p
Reapply [RemoveDIs] Read/write DbgRecords directly from/to bitcode (#83251)
Reaplying after revert in #85382 (861ebe6446296c96578807363aa292c69d827773). Fixed intermittent test failure by avoiding piping output in some RUN lines.
If --write-experimental-debuginfo-iterators-to-bitcode is true (default false) and --expermental-debuginfo-iterators is also true then the new debug info format (non-instruction records) is written to bitcode directly.
Added the following records:
FUNC_CODE_DEBUG_RECORD_LABEL FUNC_CODE_DEBUG_RECORD_VALUE FUNC_CODE_DEBUG_RECORD_DECLARE FUNC_CODE_DEBUG_RECORD_ASSIGN FUNC_CODE_DEBUG_RECORD_VALUE_SIMPLE
The last one has an abbrev in FUNCTION_BLOCK BLOCK_INFO. Incidentally, this uses the last value available without widening the code-length for FUNCTION_BLOCK from 4 to 5 bits.
Records are formatted as follows:
All DbgRecord start with: 1. DILocation
FUNC_CODE_DEBUG_RECORD_LABEL 2. DILabel
DPValues then share common fields: 2. DILocalVariable 3. DIExpression
FUNC_CODE_DEBUG_RECORD_VALUE 4. Location Metadata
FUNC_CODE_DEBUG_RECORD_DECLARE 4. Location Metadata
FUNC_CODE_DEBUG_RECORD_VALUE_SIMPLE 4. Location Value (single)
FUNC_CODE_DEBUG_RECORD_ASSIGN 4. Location Metadata 5. DIAssignID 6. DIExpression (address) 7. Location Metadata (address)
Encoding the DILocation metadata reference directly appeared to yield smaller bitcode files than encoding the operands seperately (as is done with instruction DILocations).
FUNC_CODE_DEBUG_RECORD_VALUE_SIMPLE is by far the most common DbgRecord record in optimized code (order of 5x-10x over other kinds). Unoptimized code should only contain FUNC_CODE_DEBUG_RECORD_DECLARE.
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#
861ebe64 |
| 15-Mar-2024 |
Orlando Cazalet-Hyams <orlando.hyams@sony.com> |
Revert "[RemoveDIs] Read/write DbgRecords directly from/to bitcode" (#85382)
Reverts llvm/llvm-project#83251
Buildbot: https://lab.llvm.org/buildbot/#/builders/139/builds/61485
|
#
d6d3d96b |
| 15-Mar-2024 |
Orlando Cazalet-Hyams <orlando.hyams@sony.com> |
[RemoveDIs] Read/write DbgRecords directly from/to bitcode (#83251)
If --write-experimental-debuginfo-iterators-to-bitcode is true (default false)
and --expermental-debuginfo-iterators is also true
[RemoveDIs] Read/write DbgRecords directly from/to bitcode (#83251)
If --write-experimental-debuginfo-iterators-to-bitcode is true (default false)
and --expermental-debuginfo-iterators is also true then the new debug info
format (non-instruction records) is written to bitcode directly.
Added the following records:
FUNC_CODE_DEBUG_RECORD_LABEL
FUNC_CODE_DEBUG_RECORD_VALUE
FUNC_CODE_DEBUG_RECORD_DECLARE
FUNC_CODE_DEBUG_RECORD_ASSIGN
FUNC_CODE_DEBUG_RECORD_VALUE_SIMPLE
The last one has an abbrev in FUNCTION_BLOCK BLOCK_INFO. Incidentally, this uses
the last value available without widening the code-length for FUNCTION_BLOCK
from 4 to 5 bits.
Records are formatted as follows:
All DbgRecord start with:
1. DILocation
FUNC_CODE_DEBUG_RECORD_LABEL
2. DILabel
DPValues then share common fields:
2. DILocalVariable
3. DIExpression
FUNC_CODE_DEBUG_RECORD_VALUE
4. Location Metadata
FUNC_CODE_DEBUG_RECORD_DECLARE
4. Location Metadata
FUNC_CODE_DEBUG_RECORD_VALUE_SIMPLE
4. Location Value (single)
FUNC_CODE_DEBUG_RECORD_ASSIGN
4. Location Metadata
5. DIAssignID
6. DIExpression (address)
7. Location Metadata (address)
Encoding the DILocation metadata reference directly appeared to yield smaller
bitcode files than encoding the operands seperately (as is done with instruction
DILocations).
FUNC_CODE_DEBUG_RECORD_VALUE_SIMPLE is by far the most common DbgRecord record
in optimized code (order of 5x-10x over other kinds). Unoptimized code should
only contain FUNC_CODE_DEBUG_RECORD_DECLARE.
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#
40282674 |
| 09-Mar-2024 |
Andreas Jonson <andjo403@hotmail.com> |
Reapply [IR] Add new Range attribute using new ConstantRange Attribute type (#84617)
The only change from https://github.com/llvm/llvm-project/pull/83171 is the
change of the allocator so the destr
Reapply [IR] Add new Range attribute using new ConstantRange Attribute type (#84617)
The only change from https://github.com/llvm/llvm-project/pull/83171 is the
change of the allocator so the destructor is called for
ConstantRangeAttributeImpl.
reverts https://github.com/llvm/llvm-project/pull/84549
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#
0861755e |
| 08-Mar-2024 |
Florian Mayer <fmayer@google.com> |
Revert "[IR] Add new Range attribute using new ConstantRange Attribute type" (#84549)
Reverts llvm/llvm-project#83171
broke sanitizer buildbot
https://lab.llvm.org/buildbot/#/builders/168/builds
Revert "[IR] Add new Range attribute using new ConstantRange Attribute type" (#84549)
Reverts llvm/llvm-project#83171
broke sanitizer buildbot
https://lab.llvm.org/buildbot/#/builders/168/builds/19110/steps/10/logs/stdio
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#
e0d49066 |
| 08-Mar-2024 |
Andreas Jonson <andjo403@hotmail.com> |
[IR] Add new Range attribute using new ConstantRange Attribute type (#83171)
implementation as discussed in
https://discourse.llvm.org/t/rfc-metadata-attachments-for-function-arguments/76420
|
Revision tags: llvmorg-18.1.1 |
|
#
bf08d028 |
| 02-Mar-2024 |
Daniil Kovalev <dkovalev@accesssoftek.com> |
Revert "[Dwarf] Support `__ptrauth` qualifier in metadata nodes" (#83672)
Reverts llvm/llvm-project#82363
See a build failure related to an issue discovered by memory sanitizer
(use of uninitial
Revert "[Dwarf] Support `__ptrauth` qualifier in metadata nodes" (#83672)
Reverts llvm/llvm-project#82363
See a build failure related to an issue discovered by memory sanitizer
(use of uninitialized value):
https://lab.llvm.org/buildbot/#/builders/37/builds/31965
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#
8f65e7b9 |
| 01-Mar-2024 |
Daniil Kovalev <dkovalev@accesssoftek.com> |
[Dwarf] Support `__ptrauth` qualifier in metadata nodes (#82363)
Emit `__ptrauth`-qualified types as `DIDerivedType` metadata nodes in IR
with tag `DW_TAG_LLVM_ptrauth_type`, baseType referring to
[Dwarf] Support `__ptrauth` qualifier in metadata nodes (#82363)
Emit `__ptrauth`-qualified types as `DIDerivedType` metadata nodes in IR
with tag `DW_TAG_LLVM_ptrauth_type`, baseType referring to the type
which has the qualifier applied, and the following parameters
representing the signing schema:
- `ptrAuthKey` (integer)
- `ptrAuthIsAddressDiscriminated` (boolean)
- `ptrAuthExtraDiscriminator` (integer)
- `ptrAuthIsaPointer` (boolean)
- `ptrAuthAuthenticatesNullValues` (boolean)
Co-authored-by: Ahmed Bougacha <ahmed@bougacha.org>
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Revision tags: llvmorg-18.1.0, llvmorg-18.1.0-rc4 |
|
#
cbb24e13 |
| 22-Feb-2024 |
Paul Walker <paul.walker@arm.com> |
[LLVM][IR] Add native vector support to ConstantInt & ConstantFP. (#74502)
NOTE: For brevity the following talks about ConstantInt but
everything extends to cover ConstantFP as well.
Whilst Cons
[LLVM][IR] Add native vector support to ConstantInt & ConstantFP. (#74502)
NOTE: For brevity the following talks about ConstantInt but
everything extends to cover ConstantFP as well.
Whilst ConstantInt::get() supports the creation of vectors whereby
each lane has the same value, it achieves this via other constants:
* ConstantVector for fixed-length vectors
* ConstantExprs for scalable vectors
However, ConstantExprs are being deprecated and ConstantVector is
not space efficient for larger vector types. By extending ConstantInt
we can represent vector splats by only storing the underlying scalar
value.
More specifically:
* ConstantInt gains an ElementCount variant of get().
* LLVMContext is extended to map <EC,APInt>->ConstantInt.
* BitcodeReader/Writer support is extended to allow vector types.
Whilst this patch adds the base support, more work is required
before it's production ready. For example, there's likely to be
many places where isa<ConstantInt> assumes a scalar type. Accordingly
the default behaviour of ConstantInt::get() remains unchanged but a
set of flags are added to allow wider testing and thus help with the
migration:
--use-constant-int-for-fixed-length-splat
--use-constant-fp-for-fixed-length-splat
--use-constant-int-for-scalable-splat
--use-constant-fp-for-scalable-splat
NOTE: No change is required to the bitcode format because types and
values are handled separately.
NOTE: For similar reasons as above, code generation doesn't work
out-the-box.
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Revision tags: llvmorg-18.1.0-rc3, llvmorg-18.1.0-rc2 |
|
#
dcb83692 |
| 04-Feb-2024 |
Kazu Hirata <kazu@google.com> |
[Bitcode] Use range-based for loops (NFC)
|
Revision tags: llvmorg-18.1.0-rc1, llvmorg-19-init |
|
#
26a8664e |
| 11-Jan-2024 |
Teresa Johnson <tejohnson@google.com> |
[MemProf] Handle missing tail call frames (#75823)
If tail call optimization was not disabled for the profiled binary, the
call contexts will be missing frames for tail calls. Handle this by
perfo
[MemProf] Handle missing tail call frames (#75823)
If tail call optimization was not disabled for the profiled binary, the
call contexts will be missing frames for tail calls. Handle this by
performing a limited search through tail call edges for the profiled
callee when a discontinuity is detected. The search depth is adjustable
but defaults to 5.
If we are able to identify a short sequence of tail calls, update the
graph for those calls. In the case of ThinLTO, synthesize the necessary
CallsiteInfos for carrying the cloning information to the backends.
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|
#
bf5d96c9 |
| 14-Dec-2023 |
Nikita Popov <npopov@redhat.com> |
[IR] Add dead_on_unwind attribute (#74289)
Add the `dead_on_unwind` attribute, which states that the caller will
not read from this argument if the call unwinds. This allows eliding
stores that co
[IR] Add dead_on_unwind attribute (#74289)
Add the `dead_on_unwind` attribute, which states that the caller will
not read from this argument if the call unwinds. This allows eliding
stores that could otherwise be visible on the unwind path, for example:
```
declare void @may_unwind()
define void @src(ptr noalias dead_on_unwind %out) {
store i32 0, ptr %out
call void @may_unwind()
store i32 1, ptr %out
ret void
}
define void @tgt(ptr noalias dead_on_unwind %out) {
call void @may_unwind()
store i32 1, ptr %out
ret void
}
```
The optimization is not valid without `dead_on_unwind`, because the `i32
0` value might be read if `@may_unwind` unwinds.
This attribute is primarily intended to be used on sret arguments. In
fact, I previously wanted to change the semantics of sret to include
this "no read after unwind" property (see D116998), but based on the
feedback there it is better to keep these attributes orthogonal (sret is
an ABI attribute, dead_on_unwind is an optimization attribute). This is
a reboot of that change with a separate attribute.
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