Clarify the description of the noalias attribute

The previous description of the noalias attribute did not accurately specify
the implemented semantics, and the terminology used differed unnecessarily
from that used by the C specification to define the semantics of restrict. For
the argument attribute, the semantics can be precisely specified in terms of
objects accessed through pointers based on the arguments, and this is now what
is done.

Saying that the semantics are 'slightly weaker' than that provided by C99
restrict is not really useful without further elaboration, so that has been
removed from the sentence.

noalias on a return value is really used to mean that the function is
malloc-like (and, in fact, we use this attribute to represent
__attribute__((malloc)) in Clang), and this is a stronger guarantee than that
provided by restrict (because it is a property of the pointed-to memory region,
not just a guarantee on object access). Clarifying this is relevant to fixing
(and was motivated by the discussion on) PR21556.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222497 91177308-0d34-0410-b5e6-96231b3b80d8
SROA: The alloca type isn't a candidate promotion type for vectors

The alloca's type is irrelevant, only those types which are used in a
load or store of the exact size of the slice should be considered.

This manifested as an assertion failure when we compared the various
types: we had a size mismatch.

This fixes PR21480.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222499 91177308-0d34-0410-b5e6-96231b3b80d8
This Reassociate change unintentionally slipped in r222499

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222500 91177308-0d34-0410-b5e6-96231b3b80d8
Add accessor marcos to ConstantPlaceHolder, similar to those in the base class.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222502 91177308-0d34-0410-b5e6-96231b3b80d8