tree d8abd7b0cd8cac503ed15aad02b55d25843443de
parent 75c8985876c0afa69377e4efd4c47224556a0052
author Aleksandr Popov <42888396+aleks-tmb@users.noreply.github.com> 1756368054 +0200
committer GitHub <noreply@github.com> 1756368054 +0200
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MC: Fix incorrect NOP insertion between fused instructions that breaks macro fusion (#155316)

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