Zhaoxuan Jiang 2738828c0e
[Reland] [CGData] Lazy loading support for stable function map (#154491)
This is an attempt to reland #151660 by including a missing STL header
found by a buildbot failure.

The stable function map could be huge for a large application. Fully
loading it is slow and consumes a significant amount of memory, which is
unnecessary and drastically slows down compilation especially for
non-LTO and distributed-ThinLTO setups. This patch introduces an opt-in
lazy loading support for the stable function map. The detailed changes
are:

- `StableFunctionMap`
- The map now stores entries in an `EntryStorage` struct, which includes
offsets for serialized entries and a `std::once_flag` for thread-safe
lazy loading.
- The underlying map type is changed from `DenseMap` to
`std::unordered_map` for compatibility with `std::once_flag`.
- `contains()`, `size()` and `at()` are implemented to only load
requested entries on demand.

- Lazy Loading Mechanism
- When reading indexed codegen data, if the newly-introduced
`-indexed-codegen-data-lazy-loading` flag is set, the stable function
map is not fully deserialized up front. The binary format for the stable
function map now includes offsets and sizes to support lazy loading.
- The safety of lazy loading is guarded by the once flag per function
hash. This guarantees that even in a multi-threaded environment, the
deserialization for a given function hash will happen exactly once. The
first thread to request it performs the load, and subsequent threads
will wait for it to complete before using the data. For single-threaded
builds, the overhead is negligible (a single check on the once flag).
For multi-threaded scenarios, users can omit the flag to retain the
previous eager-loading behavior.
2025-08-20 06:15:04 -07:00

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# Test no input file
RUN: not llvm-cgdata --convert --output - 2>&1 | FileCheck %s --check-prefix=NOFILE --ignore-case
NOFILE: error: No input file is specified.
# Test for empty cgdata file, which is invalid.
RUN: touch %t_emptyfile.cgtext
RUN: not llvm-cgdata --convert %t_emptyfile.cgtext --format text 2>&1 | FileCheck %s --check-prefix=EMPTY
EMPTY: {{.}}emptyfile.cgtext: empty codegen data
# Test for empty header in the text format. It can be converted to a valid binary file.
RUN: printf '#' > %t_emptyheader.cgtext
RUN: llvm-cgdata --convert %t_emptyheader.cgtext --format binary -o %t_emptyheader.cgdata
# Without any cgdata other than the header, no data shows by default.
RUN: llvm-cgdata --show %t_emptyheader.cgdata | count 0
# The version number appears when asked, as it's in the header
RUN: llvm-cgdata --show --cgdata-version %t_emptyheader.cgdata | FileCheck %s --check-prefix=VERSION
VERSION: Version: 4
# When converting a binary file (w/ the header only) to a text file, it's an empty file as the text format does not have an explicit header.
RUN: llvm-cgdata --convert %t_emptyheader.cgdata --format text | count 0
# Synthesize a header only cgdata.
# struct Header {
# uint64_t Magic;
# uint32_t Version;
# uint32_t DataKind;
# uint64_t OutlinedHashTreeOffset;
# uint64_t StableFunctionMapOffset;
# }
RUN: printf '\xffcgdata\x81' > %t_header.cgdata
RUN: printf '\x04\x00\x00\x00' >> %t_header.cgdata
RUN: printf '\x00\x00\x00\x00' >> %t_header.cgdata
RUN: printf '\x20\x00\x00\x00\x00\x00\x00\x00' >> %t_header.cgdata
RUN: printf '\x20\x00\x00\x00\x00\x00\x00\x00' >> %t_header.cgdata
RUN: diff %t_header.cgdata %t_emptyheader.cgdata