Revert r314579: "Recommi r314561 after fixing over-debug assertion".

Revert r314579: "Recommi r314561 after fixing over-debug assertion".

And follow-up r314585.
Leads to segfaults. I'll forward reproduction instructions to the patch
author.

Also, for a recommit, still add the original patch description.
Otherwise, it becomes really tedious to find out what a patch actually
does. The fact that it is a recommit with a fix is somewhat secondary.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@314622 91177308-0d34-0410-b5e6-96231b3b80d8