MC: Fix NOP insertion between fused instructions that breaks macro fusion (#155784)

In the
https://github.com/llvm/llvm-project/commit/39c8cfb70d203439e3296dfdfe3d41f1cb2ec551
patch, getOrCreateDataFragment was optimized by eagerly allocating an
empty fragment when adding a fragment with a variable-size tail. This
means that in this case the current MC fragment is no longer the one
where the instruction was inserted, and the check
`PendingBA && PendingBA->getNext() == OS.getCurrentFragment()` fails,
since CurrentFragment is now the empty fragment instead of the fragment
containing the instruction.

`PendingBA -> Fragment with a variable-size tail (contains previous
instruction) -> CurrentFragment (newly allocated empty fragment)`

This breaks the macro-fusion logic because it incorrectly assumes
another fragment has been inserted between the fused instructions.

Fixes https://github.com/llvm/llvm-project/issues/155045

#155316 Reland

0 files changed, 0 insertions, 0 deletions