This change implements support of metadata strings in operand bundle
values. It makes possible calls like:
call void @some_func(i32 %x) [ "foo"(i32 42, metadata !"abc") ]
It requires some extension of the bitcode serialization. As SSA values
and metadata are stored in different tables, there must be a way to
distinguish them during deserialization. It is implemented by putting a
special marker before the metadata index. The marker cannot be treated
as a reference to any SSA value, so it unambiguously identifies
metadata. It allows extending the bitcode serialization without breaking
compatibility.
Metadata as operand bundle values are intended to be used in
floating-point function calls. They would represent the same information
as now is passed by the constrained intrinsic arguments.
For the purpose of verifying proper arguments extensions per the target's ABI,
introduce the NoExt attribute that may be used by a target when neither sign-
or zeroextension is required (e.g. with a struct in register). The purpose of
doing so is to be able to verify that there is always one of these attributes
present and by this detecting cases where sign/zero extension is actually
missing.
As a first step, this patch has the verification step done for the SystemZ
backend only, but left off by default until all known issues have been
addressed.
Other targets/front-ends can now also add NoExt attribute where needed and do
this check in the backend.
This patch is the frontend implementation of the coroutine elide
improvement project detailed in this discourse post:
https://discourse.llvm.org/t/language-extension-for-better-more-deterministic-halo-for-c-coroutines/80044
This patch proposes a C++ struct/class attribute
`[[clang::coro_await_elidable]]`. This notion of await elidable task
gives developers and library authors a certainty that coroutine heap
elision happens in a predictable way.
Originally, after we lower a coroutine to LLVM IR, CoroElide is
responsible for analysis of whether an elision can happen. Take this as
an example:
```
Task foo();
Task bar() {
co_await foo();
}
```
For CoroElide to happen, the ramp function of `foo` must be inlined into
`bar`. This inlining happens after `foo` has been split but `bar` is
usually still a presplit coroutine. If `foo` is indeed a coroutine, the
inlined `coro.id` intrinsics of `foo` is visible within `bar`. CoroElide
then runs an analysis to figure out whether the SSA value of
`coro.begin()` of `foo` gets destroyed before `bar` terminates.
`Task` types are rarely simple enough for the destroy logic of the task
to reference the SSA value from `coro.begin()` directly. Hence, the pass
is very ineffective for even the most trivial C++ Task types. Improving
CoroElide by implementing more powerful analyses is possible, however it
doesn't give us the predictability when we expect elision to happen.
The approach we want to take with this language extension generally
originates from the philosophy that library implementations of `Task`
types has the control over the structured concurrency guarantees we
demand for elision to happen. That is, the lifetime for the callee's
frame is shorter to that of the caller.
The ``[[clang::coro_await_elidable]]`` is a class attribute which can be
applied to a coroutine return type.
When a coroutine function that returns such a type calls another
coroutine function, the compiler performs heap allocation elision when
the following conditions are all met:
- callee coroutine function returns a type that is annotated with
``[[clang::coro_await_elidable]]``.
- In caller coroutine, the return value of the callee is a prvalue that
is immediately `co_await`ed.
From the C++ perspective, it makes sense because we can ensure the
lifetime of elided callee cannot exceed that of the caller if we can
guarantee that the caller coroutine is never destroyed earlier than the
callee coroutine. This is not generally true for any C++ programs.
However, the library that implements `Task` types and executors may
provide this guarantee to the compiler, providing the user with
certainty that HALO will work on their programs.
After this patch, when compiling coroutines that return a type with such
attribute, the frontend checks that the type of the operand of
`co_await` expressions (not `operator co_await`). If it's also
attributed with `[[clang::coro_await_elidable]]`, the FE emits metadata
on the call or invoke instruction as a hint for a later middle end pass
to elide the elision.
The original patch version is
https://github.com/llvm/llvm-project/pull/94693 and as suggested, the
patch is split into frontend and middle end solutions into stacked PRs.
The middle end CoroSplit patch can be found at
https://github.com/llvm/llvm-project/pull/99283
The middle end transformation that performs the elide can be found at
https://github.com/llvm/llvm-project/pull/99285
The primary motivation is to remove `EntryCount` from `FunctionSummary`.
This frees 8 bytes out of `sizeof(FunctionSummary)` (136 bytes as of
64498c5483).
While I'm at it, this PR clean up {SummaryBasedOptimizations,
SyntheticCountsPropagation} since they were not used and there are no
plans to further invest on them.
With this patch, bitcode writer writes a placeholder 0 at the byte
offset of `EntryCount` and bitcode reader can parse the function entry
count at the correct byte offset. Added a TODO to stop writing
`EntryCount` and bump bitcode version
This reverts commit 178fc4779ece31392a2cd01472b0279e50b3a199.
This attribute was not needed now that we are using the lsan style
ScopedDisabler for disabling this sanitizer
See #106736#106125
For more discussion
This retries #90692 which was reverted previously due to issues with
lld-available being set, even if the copy of lld is not built from
source.
This does not change any code compared to #90692 to address the
lld-available issue.
The main change w.r.t, lld-available is xfailing tests in PR #99056
(until a longer term fix is available).
This patch introduces type alias ModuleToSummariesForIndexTy.
I'm planning to change the type slightly to allow heterogeneous lookup
(that is, std::map<K, V, std::less<>>) in a subsequent patch. The
problem is that changing the type affects many places. Using a type
alias reduces the impact.
DefOrUseGUIDs is used only for membership checking purposes. We don't
need std::set's strengths like iterators staying valid or the ability
to traverse in a sorted order.
While I am at it, this patch replaces count with contains for slightly
increased readability.
It is now translated to `<1 x i64>`, which allows the removal of a bunch
of special casing.
This _incompatibly_ changes the ABI of any LLVM IR function with
`x86_mmx` arguments or returns: instead of passing in mmx registers,
they will now be passed via integer registers. However, the real-world
incompatibility caused by this is expected to be minimal, because Clang
never uses the x86_mmx type -- it lowers `__m64` to either `<1 x i64>`
or `double`, depending on ABI.
This change does _not_ eliminate the SelectionDAG `MVT::x86mmx` type.
That type simply no longer corresponds to an IR type, and is used only
by MMX intrinsics and inline-asm operands.
Because SelectionDAGBuilder only knows how to generate the
operands/results of intrinsics based on the IR type, it thus now
generates the intrinsics with the type MVT::v1i64, instead of
MVT::x86mmx. We need to fix this before the DAG LegalizeTypes, and thus
have the X86 backend fix them up in DAGCombine. (This may be a
short-lived hack, if all the MMX intrinsics can be removed in upcoming
changes.)
Works towards issue #98272.
If requested, via the -memprof-report-hinted-sizes option, track the
total profiled size of each MIB through the thin link, then report on
the corresponding allocation coldness after all cloning is complete.
To save size, a different bitcode record type is used for the allocation
info when the option is specified, and the sizes are kept separate from
the MIBs in the index.
https://github.com/llvm/llvm-project/pull/87600 was reverted in order to
revert
6262763341.
Now https://github.com/llvm/llvm-project/pull/95482 is fix forward for
6262763341.
This patch is a reland for
https://github.com/llvm/llvm-project/pull/87600
**Changes on top of original patch**
In `llvm/include/llvm/IR/ModuleSummaryIndex.h`, make the type of
`GVSummaryPtrSet` an `unordered_set` which is more memory efficient when
the number of elements is smaller than 128 [1]
**Original commit message**
For distributed ThinLTO, the LTO indexing step generates combined
summary for each module, and postlink pipeline reads the combined
summary which stores the information for link-time optimization.
This patch populates the 'import type' of a summary in bitcode, and
updates bitcode reader to parse the bit correctly.
[1]
393eff4e02/llvm/lib/Support/SmallPtrSet.cpp (L43)
This patch augments the HIPAMD driver to allow it to target AMDGCN
flavoured SPIR-V compilation. It's mostly straightforward, as we re-use
some of the existing SPIRV infra, however there are a few notable
additions:
- we introduce an `amdgcnspirv` offload arch, rather than relying on
using `generic` (this is already fairly overloaded) or simply using
`spirv` or `spirv64` (we'll want to use these to denote unflavoured
SPIRV, once we bring up that capability)
- initially it is won't be possible to mix-in SPIR-V and concrete AMDGPU
targets, as it would require some relatively intrusive surgery in the
HIPAMD Toolchain and the Driver to deal with two triples
(`spirv64-amd-amdhsa` and `amdgcn-amd-amdhsa`, respectively)
- in order to retain user provided compiler flags and have them
available at JIT time, we rely on embedding the command line via
`-fembed-bitcode=marker`, which the bitcode writer had previously not
implemented for SPIRV; we only allow it conditionally for AMDGCN
flavoured SPIRV, and it is handled correctly by the Translator (it ends
up as a string literal)
Once the SPIRV BE is no longer experimental we'll switch to using that
rather than the translator. There's some additional work that'll come
via a separate PR around correctly piping through AMDGCN's
implementation of `printf`, for now we merely handle its flags
correctly.
Extend `DIBasicType` and `DISubroutineType` with additional field
`annotations`, e.g. as below:
```
!5 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed, annotations: !6)
!6 = !{!7}
!7 = !{!"btf:type_tag", !"tag1"}
```
The field would be used by BPF backend to generate DWARF attributes
corresponding to `btf_type_tag` type attributes, e.g.:
```
0x00000029: DW_TAG_base_type
DW_AT_name ("int")
DW_AT_encoding (DW_ATE_signed)
DW_AT_byte_size (0x04)
0x0000002d: DW_TAG_LLVM_annotation
DW_AT_name ("btf:type_tag")
DW_AT_const_value ("tag1")
```
Such DWARF entries would be used to generate BTF definitions by tools
like [pahole](https://github.com/acmel/dwarves).
Note: similar fields with similar purposes are already present in
DIDerivedType and DICompositeType.
Currently "btf_type_tag" attributes are represented in debug information
as 'annotations' fields in DIDerivedType with DW_TAG_pointer_type tag.
The annotation on a pointer corresponds to pointee having the attributes
in the final BTF.
The discussion in
[thread](https://lore.kernel.org/bpf/87r0w9jjoq.fsf@oracle.com/) came to
conclusion, that such annotations should apply to the annotated type
itself. Hence the necessity to extend `DIBasicType` & `DISubroutineType`
types with 'annotations' field to represent cases like below:
```
int __attribute__((btf_type_tag("foo"))) bar;
```
This was previously tracked as differential revision:
https://reviews.llvm.org/D143966
Remove support for the icmp and fcmp constant expressions.
This is part of:
https://discourse.llvm.org/t/rfc-remove-most-constant-expressions/63179
As usual, many of the updated tests will no longer test what they were
originally intended to -- this is hard to preserve when constant
expressions get removed, and in many cases just impossible as the
existence of a specific kind of constant expression was the cause of the
issue in the first place.
A cycle profile of a thin link showed a lot of time spent in sort called
from the BitcodeWriter, which was being used to compute the unique
references to stack ids in the summaries emitted for each backend in a
distributed thinlto build. We were also frequently invoking lower_bound
to locate stack id indices in the resulting vector when writing out the
referencing memprof records.
Change this to use a map to uniquify the references, and to hold the
index of the corresponding stack id in the StackIds vector, which is
now populated at the same time.
This reduced the time of a large thin link by about 10%.
PR #92983 accidentally changed the buffer allocation in
`llvm::WriteBitcodeToFile` to be allocated on the stack, which is
problematic given it's a large-ish buffer (256K)
- added unittests for the raw_fd_stream output case.
- the `BitstreamWriter` ctor was confusing, the relationship between the buffer and the file stream wasn't clear and in fact there was a potential bug in `BitcodeWriter` in the mach-o case, because that code assumed in-buffer only serialization. The incremental flushing behavior of flushing at end of block boundaries was an implementation detail that meant serializers not using blocks (for example) would need to know to check the buffer and flush. The bug was latent - in the sense that, today, because the stream being passed was not a `raw_fd_stream`, incremental buffering never kicked in.
The new design moves the responsibility of flushing to the `BitstreamWriter`, and makes it work with any `raw_ostream` (but incrementally flush only in the `raw_fd_stream` case). If the `raw_ostream` is over a buffer - i.e. a `raw_svector_stream` - then it's equivalent to today's buffer case. For all other `raw_ostream` cases, buffering is an implementation detail. In all cases, the buffer is flushed (well, in the buffer case, that's a moot statement).
This simplifies the state and state transitions the user has to track: you have a raw_ostream -> BitstreamWrite in it -> destroy the writer => the bitstream is completely written in your raw_ostream. The "buffer" case and the "raw_fd_stream" case become optimizations rather than imposing state transition concerns to the user.
This defines a new kind of IR Constant that represents a ptrauth signed
pointer, as used in AArch64 PAuth.
It allows representing most kinds of signed pointer constants used thus
far in the llvm ptrauth implementations, notably those used in the
Darwin and ELF ABIs being implemented for c/c++. These signed pointer
constants are then lowered to ELF/MachO relocations.
These can be simply thought of as a constant `llvm.ptrauth.sign`, with
the interesting addition of discriminator computation: the `ptrauth`
constant can also represent a combined blend, when both address and
integer discriminator operands are used. Both operands are otherwise
optional, with default values 0/null.
This implements the `nusw` and `nuw` flags for `getelementptr` as
proposed at
https://discourse.llvm.org/t/rfc-add-nusw-and-nuw-flags-for-getelementptr/78672.
The three possible flags are encapsulated in the new `GEPNoWrapFlags`
class. Currently this class has a ctor from bool, interpreted as the
InBounds flag. This ctor should be removed in the future, as code gets
migrated to handle all flags.
There are a few places annotated with `TODO(gep_nowrap)`, where I've had
to touch code but opted to not infer or precisely preserve the new
flags, so as to keep this as NFC as possible and make sure any changes
of that kind get test coverage when they are made.
For distributed ThinLTO, the LTO indexing step generates combined
summary for each module, and postlink pipeline reads the combined
summary which stores the information for link-time optimization.
This patch populates the 'import type' of a summary in bitcode, and
updates bitcode reader to parse the bit correctly.
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.
This reverts commit 2aabfc811670beb843074c765c056fff4a7b443b.
Add fixes to LLD and Gold tests missed in original change.
Co-authored-by: Jan Voung <jvoung@google.com>
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>
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] 3b337242ee/llvm/lib/Transforms/IPO/FunctionImport.cpp (L1608-L1764)
[3] 3b337242ee/llvm/lib/Transforms/IPO/FunctionImport.cpp (L856)
[4] 3b337242ee/llvm/lib/Linker/IRMover.cpp (L605)
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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
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.
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/`.
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.
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.
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>
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.
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.
