[AVX-512] Add a test case to show that we don't select masked vpermi2ps when...

[AVX-512] Add a test case to show that we don't select masked vpermi2ps when the index operand comes from a bitcast.

It doesn't work because we're looking for a bitcast from the v4i32 index operand to v4f32 for the passthru part of the DAG. But since the index is bitcasted from v2i64 and bitcasts fold, we actually have a bitcast from v2i64 to v4f32 in the passthru part of the DAG.

Taken from optimized output from clang's test case.

llvm-svn: 280695