[asan] Optimize accesses to global arrays with constant index

Summary:
Given a global array G[N], which is declared in this CU and has static initializer
avoid instrumenting accesses like G[i], where 'i' is a constant and 0<=i<N.
Also add a bit of stats.

This eliminates ~1% of instrumentations on SPEC2006
and also partially helps when asan is being run together with coverage.

Reviewers: samsonov

Reviewed By: samsonov

CC: llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1947

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192794 91177308-0d34-0410-b5e6-96231b3b80d8
DAGCombiner: Don't fold xor into not if getNOT would introduce an illegal constant.

This happens e.g. with <2 x i64> -1 on x86_32. It cannot be generated directly
because i64 is illegal. It would be nice if getNOT would handle this
transparently, but I don't see a way to generate a legal constant there right
now. Fixes PR17487.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192795 91177308-0d34-0410-b5e6-96231b3b80d8
Add more documentation about the TargetStreamer interface.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192796 91177308-0d34-0410-b5e6-96231b3b80d8