[PATCH] [Review Request] A module pass "PromoteHalf"

[Wan, Xiaofei]

Hi, Tim, thanks for your reply:

1. This pass will be the first pass on IR before any other transformation passes, for sure it will change the module; it only use public interface in current code infrastructure. Could you please describe the main concern here? Thanks.
2. Half float is a special type since most CPU targets don't support it in native way, most target only use half as a storage type; this is why I don't want to handle it in DAGTypeLegalizer; it is more clear to handle it before any transformation passes.
3. Handling half in DAGTypeLegalizer will add the complexity of type legalizer, it is difficult to mask/disable it in target machine configuration. The PromoteHalf pass will not be configured as default pass, it has no impact to current code infrastructure. 

Thanks
Wan Xiaofei

http://reviews.llvm.org/D4926