[all-commits] [llvm/llvm-project] 914d5a: [DTLTO] Overlap temporary file removal (#209423)

[Ben Dunbobbin via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 914d5a1841dedf2148e21bd6de3b92409fe79285
      https://github.com/llvm/llvm-project/commit/914d5a1841dedf2148e21bd6de3b92409fe79285
  Author: Ben Dunbobbin <Ben.Dunbobbin at sony.com>
  Date:   2026-07-21 (Tue, 21 Jul 2026)

  Changed paths:
    M lld/COFF/Driver.cpp
    M lld/COFF/LTO.cpp
    M lld/COFF/LTO.h
    M lld/COFF/SymbolTable.cpp
    M lld/COFF/SymbolTable.h
    M lld/ELF/Config.h
    M lld/ELF/Driver.cpp
    M lld/ELF/LTO.cpp
    M lld/ELF/LTO.h
    M llvm/include/llvm/DTLTO/DTLTO.h
    M llvm/include/llvm/LTO/LTO.h
    M llvm/lib/DTLTO/DTLTO.cpp
    M llvm/tools/llvm-lto2/llvm-lto2.cpp

  Log Message:
  -----------
  [DTLTO] Overlap temporary file removal (#209423)

Deleting the temporary files produced by the DTLTO pipeline can be
expensive on Windows hosts. For a Clang link (Debug build with
sanitizers and instrumentation) using an optimized toolchain (PGO
non-LTO, llvmorg-22.1.0) on a Windows 11 Pro (Build 26200), AMD Family
25 @ ~4.5 GHz, 16 cores/32 threads, 64 GB RAM machine, the mean duration
of the "Remove DTLTO temporary files" time trace scope was 1267.789 ms
(measured over 10 runs).

This patch performs the deletions on a background thread, allowing them
to overlap with the tail of the link to hide this cost.

This is a re-implementation of the asynchronous cleanup idea from
https://github.com/llvm/llvm-project/pull/186988, which had to be
reverted in https://github.com/llvm/llvm-project/pull/189043 because
cleanup was not guaranteed to complete before LLD invoked
timeTraceProfilerCleanup(). In certain cases timeTraceProfilerCleanup()
was called before temporary file deletion had completed in LLD, which
caused memory leaks that were flagged by sanitizer builds.

Note that the DTLTO implementation has been refactored heavily since
https://github.com/llvm/llvm-project/pull/186988, so this is a
re-implementation along the same lines.

To solve the ordering issue, LLD now calls a hook that defaults to a
no-op, and DTLTO overrides it to drain the background deletion work.
LLD calls this hook before time-trace write/cleanup.



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