llvm-project

b90a8d38 - [LoopInterchange] Add simplifyLCSSAPhis: remove phi from non-exit bb (#160889)

[LoopInterchange] Add simplifyLCSSAPhis: remove phi from non-exit bb (#160889) This deals with a corner case of LCSSA phi nodes in the outer loop latch block: the loop was in LCSSA form, some transformations can come along (e.g. unswitch) and create an empty block: BB4: br label %BB5 BB5: %old.cond.lcssa = phi i16 [ %cond, %BB4 ] br outer.header Interchange then brings it in LCSSA form again and we get: BB4: %new.cond.lcssa = phi i16 [ %cond, %BB3 ] br label %BB5 BB5: %old.cond.lcssa = phi i16 [ %new.cond.lcssa, %BB4 ] Which means that we have a chain of LCSSA phi nodes from %new.cond.lcssa to %old.cond.lcssa. The problem is that interchange can reoder blocks BB4 and BB5 placing the use before the def if we don't check this. The solution is to simplify lcssa phis, and remove them from non-exit blocks if they are 1-input phi nodes. Fixes #160068