This patch does two things:
- During deserialization, we accept a function name for Frame as an
alternative to the usual GUID expressed as a hexadecimal number.
- During serialization, we print a GUID of Frame as a 16-digit
hexadecimal number prefixed with 0x in the usual way. (Without this
patch, we print a decimal number, which is not customary.)
The patch uses a machinery called "normalization" in YAML I/O, which
lets us serialize and deserialize into an alternative data structure.
For our use case, we have an alternative Frame data structure, which
is identical to "struct Frame" except that Function is of type
GUIDHex64 instead of GlobalValue::GUID. This alternative type
supports the two bullet points above without modifying "struct Frame"
at all.
This patch does two things:
- During deserialization, we accept a function name as an alternative
to the usual GUID represented as a hexadecimal number.
- During serialization, we print a GUID as a 16-digit hexadecimal
number prefixed with 0x in the usual way. (Without this patch, we
print a decimal number, which is not customary.)
In YAML, the MemProf profile is a vector of pairs of GUID and
MemProfRecord. This patch accepts a function name for the GUID, but
it does not accept a function name for the GUID used in Frames yet.
That will be addressed in a subsequent patch.
This patch adds YAML read/write support to llvm-profdata. The primary
intent is to accommodate MemProf profiles in test cases, thereby
avoiding the binary format.
The read support is via llvm-profdata merge. This is useful when we
want to verify that the compiler does the right thing on a given .ll
file and a MemProf profile in a test case. In the test case, we would
convert the MemProf profile in YAML to an indexed profile and invoke
the compiler on the .ll file along with the indexed profile.
The write support is via llvm-profdata show --memory. This is useful
when we wish to convert an indexed MemProf profile to YAML while
writing tests. We would compile a test case in C++, run it for an
indexed MemProf profile, and then convert it to the text format.
This patch removes MemProf format Version 0 now that version 2 and 3
seem to be working well.
I'm not touching version 1 for now because some tests still rely on
version 1.
Note that Version 0 is identical to Version 1 except that the MemProf
section of the indexed format has a MemProf version field.
The Lit in subject fails on z/OS since the input file
`Inputs/split-layout.profdata` is marked as ASCII even though it is
binary and the output file `Output/sample-split-layout.test.tmp-output`
is binary.
This PR removes the diff command which fails because it compares a
binary file and a text file. The rational is that this diff command
seems to be redundant to the `FileCheck` on the next command.
Using the flag `-split_layout` in llvm-profdata merge, the output
profile can write profiles with and without inlined function into two
different extbinary sections (and their FuncOffsetTable too). The
section without inlined functions are marked with `SecFlagFlat` and is
skipped by ThinLTO because it provides no useful info.
The split layout feature was already implemented in SampleProfWriter but
previously there is no way to use it from llvm-profdata.
PR 94264 had substantial increase in test binary size. This was due to
building LLVM and compiler-rt with GCC, implicitly causing the runtimes
to be built with full debuginfo. Rebuilding LLVM with
`-DCMAKE_CXX_COMPILER=/usr/bin/clang++` and regenerating .exe files with
script `update_memprof_inputs.sh` avoids this increase in test binary
size.
- The indexed iFDO profiles contains compressed vtable names for `llvm-profdata show --show-vtables` debugging
usage. An optimized build doesn't need it and doesn't decompress the blob now [1], since optimized binary has the
source code and IR to find vtable symbols.
- The motivation is to avoid increasing profile size when it's not necessary.
- This doesn't change the indexed profile format and thereby doesn't need a version change.
[1] eac925fb81/llvm/include/llvm/ProfileData/InstrProfReader.h (L696-L699)
Adds compile time flag -mllvm -memprof-histogram and runtime flag
histogram=true|false to turn Histogram collection on and off. The
-memprof-histogram flag relies on -memprof-use-callbacks=true to work.
Updates shadow mapping logic in histogram mode from having one 8 byte
counter for 64 bytes, to 1 byte for 8 bytes, capped at 255. Only
supports this granularity as of now.
Updates the RawMemprofReader and serializing MemoryInfoBlocks to binary
format, including changing to a new version of the raw binary format
from version 3 to version 4.
Updates creating MemoryInfoBlocks with and without Histograms. When two
MemoryInfoBlocks are merged, AccessCounts are summed up and the shorter
Histogram is removed.
Adds a memprof_histogram test case.
Initial commit for adding AccessCountHistograms up until RawProfile for
memprof
This patch adds Version 3 for development purposes. For now, this
patch adds V3 as a copy of V2.
For the most part, this patch adds "case Version3:" wherever "case
Version2:" appears. One exception is writeMemProfV3, which is copied
from writeMemProfV2 but updated to write out memprof::Version3 to the
MemProf header. We'll incrementally modify writeMemProfV3 in
subsequent patches.
The `llvm-profdata order` command is used to compute a function order
using traces from the input profile. Add the `--num-test-traces` flag to
keep aside N traces to evalute this order. These test traces are assumed
to be the actual function execution order in some experiment. The output
is a number that represents how many page faults we got. Lower is
better.
I tested on a large profile I already had.
```
llvm-profdata order default.profdata --num-test-traces=30
# Ordered 149103 functions
# Total area under the page fault curve: 2.271827e+09
...
```
I also improved `TemporalProfTraceTy::createBPFunctionNodes()` in a few
ways:
* Simplified how `UN`s are computed
* Change how the initial `Node` order is computed
* Filter out rare and common `UN`s
* Output vector is an aliased argument instead of a return
These changes slightly improved the evaluation in my test.
```
llvm-profdata order default.profdata --num-test-traces=30
# Ordered 149103 functions
# Total area under the page fault curve: 2.268586e+09
...
```
The `--temporal-profile-max-trace-length=0` flag in the `llvm-profdata
merge` command is used to remove traces from a profile. There was a bug
where traces would not be cleared if the profile was already sampled.
This patch fixes that.
Curently, the compiler only uses several fields of MemoryInfoBlock.
Serializing all fields into the indexed MemProf file simply wastes
storage.
This patch limits the schema down to four fields for Version2 by
default. It retains the old behavior of serializing all fields via:
llvm-profdata merge --memprof-version=2 --memprof-full-schema
This patch reduces the size of the indexed MemProf profile I have by
40% (1.6GB down to 1.0GB).
This patch adds Version2 of the indexed MemProf format. The new
format comes with a hash table from CallStackId to actual call stacks
llvm::SmallVector<FrameId>. The rest of the format refers to call
stacks with CallStackId. This "values + references" model effectively
deduplicates call stacks. Without this patch, a large indexed memprof
file of mine shrinks from 4.4GB to 1.6GB, a 64% reduction.
This patch does not make Version2 generally available yet as I am
planning to make a few more changes to the format.
(The profile format change is split into a standalone change into https://github.com/llvm/llvm-project/pull/81691)
* For InstrFDO value profiling, implement instrumentation and lowering for virtual table address.
* This is controlled by `-enable-vtable-value-profiling` and off by default.
* When the option is on, raw profiles will carry serialized `VTableProfData` structs and compressed vtables as payloads.
* Implement profile reader and writer support
* Raw profile reader is used by `llvm-profdata` but not compiler. Raw profile reader will construct InstrProfSymtab with symbol names, and map profiled runtime address to vtable symbols.
* Indexed profile reader is used by `llvm-profdata` and compiler. When initialized, the reader stores a pointer to the beginning of in-memory compressed vtable names and the length of string. When used in `llvm-profdata`, reader decompress the string to show symbols of a profiled site. When used in compiler, string decompression doesn't
happen since IR is used to construct InstrProfSymtab.
* Indexed profile writer collects the list of vtable names, and stores that to index profiles.
* Text profile reader and writer support are added but mostly follow the implementation for indirect-call value type.
* `llvm-profdata show -show-vtables <args> <profile>` is implemented.
rfc in
https://discourse.llvm.org/t/rfc-dynamic-type-profiling-and-optimizations-in-llvm/74600#pick-instrumentation-points-and-instrument-runtime-types-7
Enable temporary support to ease use of new llvm-profdata with slightly
older indexed profiles after 16e74fd48988ac95551d0f64e1b36f78a82a89a2,
which bumped the indexed format for type profiling.
Several profdata tests pass the byte 012 to printf. This causes these
tests to fail when using GnuWin32's version of printf because printf
will detect that 012 is the LF character and will prepend the byte 015
(CR) in front of LF.
This change is required after
https://github.com/llvm/llvm-project/pull/82711 which bumped the version
number.
New change on top of [reviewed
patch](https://github.com/llvm/llvm-project/pull/81691) are [in commits
after this
one](d0757f46b3).
Previous commits are restored from the remote branch with timestamps.
1. Fix build breakage for non-ELF platforms, by defining the missing
functions {`__llvm_profile_begin_vtables`, `__llvm_profile_end_vtables`,
`__llvm_profile_begin_vtabnames `, `__llvm_profile_end_vtabnames`}
everywhere.
* Tested on mac laptop (for darwins) and Windows. Specifically,
functions in `InstrProfilingPlatformWindows.c` returns `NULL` to make it
more explicit that type prof isn't supported; see comments for the
reason.
* For the rest (AIX, other), mostly follow existing examples (like this
[one](f95b2f1acf))
2. Rename `__llvm_prf_vtabnames` -> `__llvm_prf_vns` for shorter section
name, and make returned pointers
[const](a825d2a4ec (diff-4de780ce726d76b7abc9d3353aef95013e7b21e7bda01be8940cc6574fb0b5ffR120-R121))
**Original Description**
* Raw profile format
- Header: records the byte size of compressed vtable names, and the
number of profiled vtable entries (call it `VTableProfData`). Header
also records padded bytes of each section.
- Payload: adds a section for compressed vtable names, and a section to
store `VTableProfData`. Both sections are padded so the size is a
multiple of 8.
* Indexed profile format
- Header: records the byte offset of compressed vtable names.
- Payload: adds a section to store compressed vtable names. This section
is used by `llvm-profdata` to show the list of vtables profiled for an
instrumented site.
[The originally reviewed
patch](https://github.com/llvm/llvm-project/pull/66825) will have
profile reader/write change and llvm-profdata change.
- To ensure this PR has all the necessary profile format change along
with profile version bump, created a copy of the originally reviewed
patch in https://github.com/llvm/llvm-project/pull/80761. The copy
doesn't have profile format change, but it has the set of tests which
covers type profile generation, profile read and profile merge. Tests
pass there.
rfc in
https://discourse.llvm.org/t/rfc-dynamic-type-profiling-and-optimizations-in-llvm/74600
---------
Co-authored-by: modiking <modiking213@gmail.com>
* Raw profile format
- Header: records the byte size of compressed vtable names, and the
number of profiled vtable entries (call it `VTableProfData`). Header
also records padded bytes of each section.
- Payload: adds a section for compressed vtable names, and a section to
store `VTableProfData`. Both sections are padded so the size is a
multiple of 8.
* Indexed profile format
- Header: records the byte offset of compressed vtable names.
- Payload: adds a section to store compressed vtable names. This section
is used by `llvm-profdata` to show the list of vtables profiled for an
instrumented site.
[The originally reviewed
patch](https://github.com/llvm/llvm-project/pull/66825) will have
profile reader/write change and llvm-profdata change.
- To ensure this PR has all the necessary profile format change along
with profile version bump, created a copy of the originally reviewed
patch in https://github.com/llvm/llvm-project/pull/80761. The copy
doesn't have profile format change, but it has the set of tests which
covers type profile generation, profile read and profile merge. Tests
pass there.
rfc in
https://discourse.llvm.org/t/rfc-dynamic-type-profiling-and-optimizations-in-llvm/74600
---------
Co-authored-by: modiking <modiking213@gmail.com>
`--function=<regex>` Include functions matching regex in the output
`--no-function=<regex>` Exclude functions matching regex from the output
If both are specified, `--no-function` has a higher precedence if a
function name matches both filters
When merging instrFDO profiles with afdo profile as supplementary, instrFDO counters for static functions are stored with function's PGO name (with filename.cpp; prefix).
- This pull request fixes the delimiter used when a PGO function name is 'normalized' for AFDO look-up.
This patch splits a couple of lines of printf into four for
readability so that each corresponds to one field or padding. They
correspond to NumCounters, NumValueSites, NumBitmapBytes, and padding,
respectively.
This patch splits a couple of lines of printf into four for
readability so that each corresponds to one field or padding. They
correspond to NumCounters, NumValueSites, NumBitmapBytes, and padding,
respectively.
These tests generally use one printf for each field of
RawInstrProf::ProfileData except the lines being touched in this
patch. These lines print two fields, namely NumValueSites and
NumBitmapBytes, with one printf, which is very confusing. (Note that
the 4-byte printf at the end of the group is padding to make the
struct size a multiple of 8 bytes.)
This patch makes the tests a litle more readable by splitting
NumValueSites and NumBitmapBytes into two separate lines.
Part 1 of 3. This includes the LLVM back-end processing and profile
reading/writing components. compiler-rt changes are included.
Differential Revision: https://reviews.llvm.org/D138846
This seems to cause Clang to crash, see comments on the code review. Reverting
until the problem can be investigated.
> Part 1 of 3. This includes the LLVM back-end processing and profile
> reading/writing components. compiler-rt changes are included.
>
> Differential Revision: https://reviews.llvm.org/D138846
This reverts commit a50486fd736ab2fe03fcacaf8b98876db77217a7.
Part 1 of 3. This includes the LLVM back-end processing and profile
reading/writing components. compiler-rt changes are included.
Differential Revision: https://reviews.llvm.org/D138846
This is phase 1 of multiple planned improvements on the sample profile loader. The major change is to use MD5 hash code ((instead of the function itself) as the key to look up the function offset table and the profiles, which significantly reduce the time it takes to construct the map.
The optimization is based on the fact that many practical sample profiles are using MD5 values for function names to reduce profile size, so we shouldn't need to convert the MD5 to a string and then to a SampleContext and use it as the map's key, because it's extremely slow.
Several changes to note:
(1) For non-CS SampleContext, if it is already MD5 string, the hash value will be its integral value, instead of hashing the MD5 again. In phase 2 this is going to be optimized further using a union to represent MD5 function (without converting it to string) and regular function names.
(2) The SampleProfileMap is a wrapper to *map<uint64_t, FunctionSamples>, while providing interface allowing using SampleContext as key, so that existing code still work. It will check for MD5 collision (unlikely but not too unlikely, since we only takes the lower 64 bits) and handle it to at least guarantee compilation correctness (conflicting old profile is dropped, instead of returning an old profile with inconsistent context). Other code should not try to use MD5 as key to access the map directly, because it will not be able to handle MD5 collision at all. (see exception at (5) )
(3) Any SampleProfileMap::emplace() followed by SampleContext assignment if newly inserted, should be replaced with SampleProfileMap::Create(), which does the same thing.
(4) Previously we ensure an invariant that in SampleProfileMap, the key is equal to the Context of the value, for profile map that is eventually being used for output (as in llvm-profdata/llvm-profgen). Since the key became MD5 hash, only the value keeps the context now, in several places where an intermediate SampleProfileMap is created, each new FunctionSample's context is set immediately after insertion, which is necessary to "remember" the context otherwise irretrievable.
(5) When reading a profile, we cache the MD5 values of all functions, because they are used at least twice (one to index into FuncOffsetTable, the other into SampleProfileMap, more if there are additional sections), in this case the SampleProfileMap is directly accessed with MD5 value so that we don't recalculate it each time (expensive)
Performance impact:
When reading a ~1GB extbinary profile (fixed length MD5, not compressed) with 10 million function names and 2.5 million top level functions (non CS functions, each function has varying nesting level from 0 to 20), this patch improves the function offset table loading time by 20%, and improves full profile read by 5%.
Reviewed By: davidxl, snehasish
Differential Revision: https://reviews.llvm.org/D147740
This is phase 1 of multiple planned improvements on the sample profile loader. The major change is to use MD5 hash code ((instead of the function itself) as the key to look up the function offset table and the profiles, which significantly reduce the time it takes to construct the map.
The optimization is based on the fact that many practical sample profiles are using MD5 values for function names to reduce profile size, so we shouldn't need to convert the MD5 to a string and then to a SampleContext and use it as the map's key, because it's extremely slow.
Several changes to note:
(1) For non-CS SampleContext, if it is already MD5 string, the hash value will be its integral value, instead of hashing the MD5 again. In phase 2 this is going to be optimized further using a union to represent MD5 function (without converting it to string) and regular function names.
(2) The SampleProfileMap is a wrapper to *map<uint64_t, FunctionSamples>, while providing interface allowing using SampleContext as key, so that existing code still work. It will check for MD5 collision (unlikely but not too unlikely, since we only takes the lower 64 bits) and handle it to at least guarantee compilation correctness (conflicting old profile is dropped, instead of returning an old profile with inconsistent context). Other code should not try to use MD5 as key to access the map directly, because it will not be able to handle MD5 collision at all. (see exception at (5) )
(3) Any SampleProfileMap::emplace() followed by SampleContext assignment if newly inserted, should be replaced with SampleProfileMap::Create(), which does the same thing.
(4) Previously we ensure an invariant that in SampleProfileMap, the key is equal to the Context of the value, for profile map that is eventually being used for output (as in llvm-profdata/llvm-profgen). Since the key became MD5 hash, only the value keeps the context now, in several places where an intermediate SampleProfileMap is created, each new FunctionSample's context is set immediately after insertion, which is necessary to "remember" the context otherwise irretrievable.
(5) When reading a profile, we cache the MD5 values of all functions, because they are used at least twice (one to index into FuncOffsetTable, the other into SampleProfileMap, more if there are additional sections), in this case the SampleProfileMap is directly accessed with MD5 value so that we don't recalculate it each time (expensive)
Performance impact:
When reading a ~1GB extbinary profile (fixed length MD5, not compressed) with 10 million function names and 2.5 million top level functions (non CS functions, each function has varying nesting level from 0 to 20), this patch improves the function offset table loading time by 20%, and improves full profile read by 5%.
Reviewed By: davidxl, snehasish
Differential Revision: https://reviews.llvm.org/D147740
If two functions are inserted to the same bucket, their order in the
serialized profile is dependent on StringMap iteration order, which is
not guaranteed to be deterministic.
(https://llvm.org/docs/ProgrammersManual.html#llvm-adt-stringmap-h).
Use a sort like we do in writeText.
This is phase 1 of multiple planned improvements on the sample profile loader. The major change is to use MD5 hash code ((instead of the function itself) as the key to look up the function offset table and the profiles, which significantly reduce the time it takes to construct the map.
The optimization is based on the fact that many practical sample profiles are using MD5 values for function names to reduce profile size, so we shouldn't need to convert the MD5 to a string and then to a SampleContext and use it as the map's key, because it's extremely slow.
Several changes to note:
(1) For non-CS SampleContext, if it is already MD5 string, the hash value will be its integral value, instead of hashing the MD5 again. In phase 2 this is going to be optimized further using a union to represent MD5 function (without converting it to string) and regular function names.
(2) The SampleProfileMap is a wrapper to *map<uint64_t, FunctionSamples>, while providing interface allowing using SampleContext as key, so that existing code still work. It will check for MD5 collision (unlikely but not too unlikely, since we only takes the lower 64 bits) and handle it to at least guarantee compilation correctness (conflicting old profile is dropped, instead of returning an old profile with inconsistent context). Other code should not try to use MD5 as key to access the map directly, because it will not be able to handle MD5 collision at all. (see exception at (5) )
(3) Any SampleProfileMap::emplace() followed by SampleContext assignment if newly inserted, should be replaced with SampleProfileMap::Create(), which does the same thing.
(4) Previously we ensure an invariant that in SampleProfileMap, the key is equal to the Context of the value, for profile map that is eventually being used for output (as in llvm-profdata/llvm-profgen). Since the key became MD5 hash, only the value keeps the context now, in several places where an intermediate SampleProfileMap is created, each new FunctionSample's context is set immediately after insertion, which is necessary to "remember" the context otherwise irretrievable.
(5) When reading a profile, we cache the MD5 values of all functions, because they are used at least twice (one to index into FuncOffsetTable, the other into SampleProfileMap, more if there are additional sections), in this case the SampleProfileMap is directly accessed with MD5 value so that we don't recalculate it each time (expensive)
Performance impact:
When reading a ~1GB extbinary profile (fixed length MD5, not compressed) with 10 million function names and 2.5 million top level functions (non CS functions, each function has varying nesting level from 0 to 20), this patch improves the function offset table loading time by 20%, and improves full profile read by 5%.
Reviewed By: davidxl, snehasish
Differential Revision: https://reviews.llvm.org/D147740
This is phase 1 of multiple planned improvements on the sample profile loader. The major change is to use MD5 hash code ((instead of the function itself) as the key to look up the function offset table and the profiles, which significantly reduce the time it takes to construct the map.
The optimization is based on the fact that many practical sample profiles are using MD5 values for function names to reduce profile size, so we shouldn't need to convert the MD5 to a string and then to a SampleContext and use it as the map's key, because it's extremely slow.
Several changes to note:
(1) For non-CS SampleContext, if it is already MD5 string, the hash value will be its integral value, instead of hashing the MD5 again. In phase 2 this is going to be optimized further using a union to represent MD5 function (without converting it to string) and regular function names.
(2) The SampleProfileMap is a wrapper to *map<uint64_t, FunctionSamples>, while providing interface allowing using SampleContext as key, so that existing code still work. It will check for MD5 collision (unlikely but not too unlikely, since we only takes the lower 64 bits) and handle it to at least guarantee compilation correctness (conflicting old profile is dropped, instead of returning an old profile with inconsistent context). Other code should not try to use MD5 as key to access the map directly, because it will not be able to handle MD5 collision at all. (see exception at (5) )
(3) Any SampleProfileMap::emplace() followed by SampleContext assignment if newly inserted, should be replaced with SampleProfileMap::Create(), which does the same thing.
(4) Previously we ensure an invariant that in SampleProfileMap, the key is equal to the Context of the value, for profile map that is eventually being used for output (as in llvm-profdata/llvm-profgen). Since the key became MD5 hash, only the value keeps the context now, in several places where an intermediate SampleProfileMap is created, each new FunctionSample's context is set immediately after insertion, which is necessary to "remember" the context otherwise irretrievable.
(5) When reading a profile, we cache the MD5 values of all functions, because they are used at least twice (one to index into FuncOffsetTable, the other into SampleProfileMap, more if there are additional sections), in this case the SampleProfileMap is directly accessed with MD5 value so that we don't recalculate it each time (expensive)
Performance impact:
When reading a ~1GB extbinary profile (fixed length MD5, not compressed) with 10 million function names and 2.5 million top level functions (non CS functions, each function has varying nesting level from 0 to 20), this patch improves the function offset table loading time by 20%, and improves full profile read by 5%.
Reviewed By: davidxl, snehasish
Differential Revision: https://reviews.llvm.org/D147740
Balanced Partitioning tests, added by 1794532bb942, currently
hang on ARM, what causes check-all to never finish.
Issue #63168
Differential Revision: https://reviews.llvm.org/D147812
In [0] we described an algorithm called //BalancedPartitioning// (bp) to consume function traces [1] and compute a function order that reduces the number of page faults during startup.
This patch adds the `order` command to the `llvm-profdata` tool which uses bp to output a function order that can be passed to the linker via `--symbol-ordering-file=`.
Special thanks to Sergey Pupyrev and Julian Mestre for designing this balanced partitioning algorithm.
[0] https://discourse.llvm.org/t/rfc-temporal-profiling-extension-for-irpgo/68068
[1] https://reviews.llvm.org/D147287
Reviewed By: spupyrev
Differential Revision: https://reviews.llvm.org/D147812
The `llvm-profdata --version` output now looks like:
llvm-profdata
LLVM (http://llvm.org/):
LLVM version 17.0.0git
Optimized build with assertions.
This makes llvm-profdata more consistent with other tools.
Reviewed By: simon_tatham
Differential Revision: https://reviews.llvm.org/D150964
This is a follow-up to b71edfaa4ec3c998aadb35255ce2f60bba2940b0
since I forgot the lit.local.cfg files in that one.
Reformatting is done with `black`.
If you end up having problems merging this commit because you
have made changes to a python file, the best way to handle that
is to run git checkout --ours <yourfile> and then reformat it
with black.
If you run into any problems, post to discourse about it and
we will try to help.
RFC Thread below:
https://discourse.llvm.org/t/rfc-document-and-standardize-python-code-style
Reviewed By: barannikov88, kwk
Differential Revision: https://reviews.llvm.org/D150762
Cleanup profile reader classes to prepare for complex refactoring as propsed in D147740 (Use MD5 as key for profile map). Change is too complicated so I am cleaning up the reader implementation first with these goals.
- Reduce duplicated/similar logic
- Reduce virtual functions, changing them to non-virtual
- Reduce unnecessry checks, indirections, and dead writes.
This is patch 1/n. This patch refactors NameTable
Explaining several decisions here
1. useMD5() means whether names of the profiles (the ProfileMap) are represented as MD5. It is NOT whether the input profile format is MD5. This function is an interface for IPO passes to decide whether to match function names or function MD5. There are two motives here:
(a) Eventually we want to use MD5 to represent all function contexts because it is much faster to use it as a key for lookup tables (prototype implementation D147740), so in compilation mode we call setProfileUseMD5() to force use MD5. While in tools mode (llvm-profdata) we want to keep the function name info if it's in the input profile.
(b) We also propose to allow multiple name tables and profile sections in ExtBinary format, and it could consist of name tables with or without using MD5, in this case MD5 prevails and other name tables are converted to MD5.
2. MD5 handling logic is pushed up to BinaryReader base class, because this trades a non-devirtualized virtual function call with a predictable branch. ReadStringFromTable() accounts for >5% time when loading a full 1 GB profile, it should not be virtual.
Reviewed By: davidxl
Differential Revision: https://reviews.llvm.org/D148868
