intel/llvm

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Matthias Springer e6110cb339 [mlir][Transforms] Fix crash in -remove-dead-values on private functions (#169269 )

This commit fixes two crashes in the `-remove-dead-values` pass related
to private functions.

Private functions are considered entirely "dead" by the liveness
analysis, which drives the `-remove-dead-values` pass.

The `-remove-dead-values` pass removes dead block arguments from private
functions. Private functions are entirely dead, so all of their block
arguments are removed. However, the pass did not correctly update all
users of these dropped block arguments.

1. A side-effecting operation must be removed if one of its operands is
dead. Otherwise, the operation would end up with a NULL operand. Note:
The liveness analysis would not have marked an SSA value as "dead" if it
had a reachable side-effecting users. (Therefore, it is safe to erase
such side-effecting operations.)
2. A branch operation must be removed if one of its non-forwarded
operands is dead. (E.g., the condition value of a `cf.cond_br`.)
Whenever a terminator is removed, a `ub.unrechable` operation is
inserted. This fixes #158760.

2025-12-03 08:35:05 +01:00