Teach instcombine to increase the alignment of memset/memcpy/memmove when the pointer is known to come from either a global variable, alloca or malloc.  This allows us to compile this:
Teach instcombine to increase the alignment of memset/memcpy/memmove when
the pointer is known to come from either a global variable, alloca or
malloc.  This allows us to compile this:

  P = malloc(28);
  memset(P, 0, 28);

into explicit stores on PPC instead of a memset call.


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@26577 91177308-0d34-0410-b5e6-96231b3b80d8

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