Commit Graph

1 Commits

Author SHA1 Message Date
Matt Arsenault d886da042c RegisterCoalescer: Prune undef subranges from copy pairs in loops
If we had a pair of copies inside a loop which introduced new liveness
to a subregister which was undef before the loop, we would have a
dummy phi-only segment remaining across the loop body. Later, this
false segment would confuse RenameIndependentSubregs causing it to
introduce IMPLICIT_DEFs with broken value numbering.

It seems always adding the lanes to ShrinkMask is OK, so any
conditions should be purely a compile time filter.
2021-02-03 13:42:53 -05:00