[llvm] [SCEV] Add implicit guard conditions when applying loop guards. (PR #84309)

[Philip Reames via llvm-commits]

preames wrote:

Happened to chat w/Craig, and he reminded me I hadn't replied here.

This patch is not unreasonable, but there's a couple things which need done.

First, you're modifying code which is not enabled by default.  The first step is assessing the compile time impact of enabling it.  If that is prohibitive, then the rest of this line of work is moot.

Second, you're actual change appears to be three independent pieces.  Each of these should be their own review with targeted tests for each case.  Two of them appear blocked on enabling the disabled piece of code, one you could maybe do in parallel.  

I don't plan on devoting any review time to this until the first item has been resolved.

https://github.com/llvm/llvm-project/pull/84309