AMD64 front end: translate AVX2 PMASKMOV load instructions (vector
conditional loads) using IR conditional load statements IRLoadG rather
than the previous rather ingenious hack.

AMD64 back end:
* Add instruction selection etc for 32- and 64-bit conditional loads (IRLoadG)
* Handle dirty helper calls that return a value and that are conditional.  These
  result from Memcheck's instrumentation of IRLoadGs.

No functional change.  This is a cleanup as part of supporting AVX2
PMASKMOV loads and stores by using the existing IR facilities for
conditional loads and stores.

git-svn-id: svn:// 8f6e269a-dfd6-0310-a8e1-e2731360e62c
4 files changed