[all-commits] [llvm/llvm-project] f1aa60: MCFragment: Use trailing data for fixed-size part

[Fangrui Song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: f1aa6050bd90f8ec4273da55d362e23905ad3a81
      https://github.com/llvm/llvm-project/commit/f1aa6050bd90f8ec4273da55d362e23905ad3a81
  Author: Fangrui Song <i at maskray.me>
  Date:   2025-08-02 (Sat, 02 Aug 2025)

  Changed paths:
    M llvm/include/llvm/MC/MCObjectStreamer.h
    M llvm/include/llvm/MC/MCSection.h
    M llvm/lib/MC/MCObjectStreamer.cpp
    M llvm/lib/MC/MCWin64EH.cpp
    M llvm/lib/MC/MCWinCOFFStreamer.cpp
    M llvm/lib/Target/Mips/MCTargetDesc/MipsTargetStreamer.cpp
    A llvm/test/MC/ELF/many-instructions.s

  Log Message:
  -----------
  MCFragment: Use trailing data for fixed-size part

Reapply after #151724 switched to `char *Data`, fixing a
-fsanitize=pointer-overflow issue in MCAssembler::layout.

---

The fixed-size content of the MCFragment object is now stored as
trailing data, replacing ContentStart/ContentEnd with ContentSize. The
available space for trailing data is tracked using `FragSpace`. If the
available space is insufficient, a new block is allocated within the
bump allocator `MCObjectStreamer::FragStorage`.

FragList::Tail cannot be reused when switching sections or subsections,
as it is not associated with the fragment space tracked by `FragSpace`.
Instead, allocate a new fragment, which becomes less expensive after #150574.

Data can only be appended to the tail fragment of a subsection, not to
fragments in the middle. Post-assembler-layout adjustments (such as
.llvm_addrsig and .llvm.call-graph-profile) have been updated to use the
variable-size part instead.

Pull Request: https://github.com/llvm/llvm-project/pull/150846



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