Improve what can be promoted in LICM.

Summary:
In case of non-alloca pointers, we check for whether it is a pointer
from malloc-like calls and it is not captured. In such case, we can
promote the pointer, as the caller will have no way to access this pointer
even if there is unwinding in middle of the loop.

Reviewers: hfinkel, sanjoy, reames, eli.friedman

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D28834

llvm-svn: 292510