[ADT] fail-fast iterators for DenseMap
This patch was landed in r231035 and reverted because it was buggy.
This is fixed version of the same change.
Summary:
This patch is an attempt at making `DenseMapIterator`s "fail-fast".
Fail-fast iterators that have been invalidated due to insertion into
the host `DenseMap` deterministically trip an assert (in debug mode)
on access, instead of non-deterministically hitting memory corruption
issues.
Reviewers: dexonsmith, dberlin, ruiu, chandlerc
Reviewed By: chandlerc
Subscribers: yaron.keren, chandlerc, llvm-commits
Differential Revision: http://reviews.llvm.org/D7931
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231125
91177308-0d34-0410-b5e6-
96231b3b80d8