[llvm] improve debug messages in delinearization and dependence analysis (PR #156339)

[Sjoerd Meijer via llvm-commits]

================
@@ -354,18 +354,27 @@ void llvm::computeAccessFunctions(ScalarEvolution &SE, const SCEV *Expr,
     if (!AR->isAffine())
       return;
 
+  // Clear output vector.
+  Subscripts.clear();
----------------
sjoerdmeijer wrote:

I was going to say that we should add NFC to the subject line, until I noticed this one here. 
That looks like it is fixing a bug? I see the same pattern of clearing `Subscripts` and `Sizes` in the other functions below. As a minimum, I think it is worth documenting this API change in the header file and comments?

https://github.com/llvm/llvm-project/pull/156339