[VectorCombine] foldShuffleOfShuffles - fold shuffle(shuffle(x,y),poison) length changing masks (#144690)

The shuffle merging code assumes that the shuffle sources are all the
same type, which fails if we've changed length and don't have 2 inner
shuffles. We already handle length-changing shuffles if we do have 2
inner shuffles.

This patch creates a fake "all poison" shuffle mask and reuses the other
shuffle's sources, which can be safely used with the existing merge
code.

The alternative was a considerable refactor of the merge code to account
for different vector widths......

Fixes #144656

0 files changed, 0 insertions, 0 deletions