[SystemZ] Make better use of VLLEZ
This patch fixes two deficiencies in current code that recognizes
the VLLEZ idiom:
- For the floating-point versions, we have ISel patterns that match
on a bitconvert as the top node. In more complex cases, that
bitconvert may already have been merged into something else.
Fix the patterns to match the inner nodes instead.
- For the 64-bit integer versions, depending on the surrounding code,
we may get either a DAG tree based on JOIN_DWORDS or one based on
INSERT_VECTOR_ELT. Use a PatFrags to simply match both variants.
llvm-svn: 349749