[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.

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/TargetFrameLoweringImpl.cpp b/llvm/lib/CodeGen/TargetFrameLoweringImpl.cpp
index 08e86c7..5784974 100644
--- a/llvm/lib/CodeGen/TargetFrameLoweringImpl.cpp
+++ b/llvm/lib/CodeGen/TargetFrameLoweringImpl.cpp
@@ -35,7 +35,7 @@ bool TargetFrameLowering::enableCalleeSaveSkip(const MachineFunction &MF) const
   return false;
 }
 
-bool TargetFrameLowering::enableCFIFixup(MachineFunction &MF) const {
+bool TargetFrameLowering::enableCFIFixup(const MachineFunction &MF) const {
   return MF.needsFrameMoves() &&
          !MF.getTarget().getMCAsmInfo()->usesWindowsCFI();
 }