[all-commits] [llvm/llvm-project] 3a22cf: [CFIFixup] Fixup CFI for split functions with sync...

[Daniel Hoekwater via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 3a22cf9bd85f77b5274304eda6f90d758f0a6664
      https://github.com/llvm/llvm-project/commit/3a22cf9bd85f77b5274304eda6f90d758f0a6664
  Author: Daniel Hoekwater <hoekwater at google.com>
  Date:   2025-02-11 (Tue, 11 Feb 2025)

  Changed paths:
    M llvm/include/llvm/CodeGen/TargetFrameLowering.h
    M llvm/lib/CodeGen/CFIFixup.cpp
    M llvm/lib/CodeGen/TargetFrameLoweringImpl.cpp
    M llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
    M llvm/lib/Target/AArch64/AArch64FrameLowering.h
    M llvm/test/CodeGen/AArch64/cfi-fixup-multi-section.mir

  Log Message:
  -----------
  [CFIFixup] Fixup CFI for split functions with synchronous uwtables (#125299)

- **Precommit tests for synchronous uwtable CFI fixup**
- **[CFIFixup] Fixup CFI for split functions with synchronous uwtables**

Commit
https://github.com/llvm/llvm-project/commit/6e54fccede402c9ed0e8038aa258a99c5a2773e5
disables CFI fixup for
functions with synchronous tables, breaking CFI for split functions.
Instead, we can disable *block-level* CFI fixup for functions with
synchronous tables.

Unwind tables can be:
- N/A (not present)
- Asynchronous
- Synchronous

Functions without unwind tables don't need CFI fixup (since they don't
care about CFI).

Functions with asynchronous unwind tables must be accurate for each
basic block, so full CFI fixup is necessary.

Functions with synchronous unwind tables only need to be accurate for
each function (specifically, the portion of a function in a given
section). Disabling CFI fixup entirely for functions with synchronous
uwtables may break CFI for a function split between two sections. The
portion in the first section may have valid CFI, while the portion in
the second section is missing a call frame.

Ex:
```
(.text.hot)
Foo (BB1):
  <Call frame information>
  ...
BB2:
  ...

(.text.split)
BB3:
  ...
BB4:
  <epilogue>
```

Even if `Foo` has a synchronous unwind table, we still need to insert
call frame information into `BB3` so that unwinding the call stack from
`BB3` or `BB4` works properly.



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