[llvm-mca] Do not assume that implicit reads cannot be associated with ReadAdvance entries.

Before, the instruction builder incorrectly assumed that only explicit reads
could have been associated with ReadAdvance entries.
This patch fixes the issue and adds a test to verify it.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@328972 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed