[llvm] [DA] Check for overflow in strong SIV test (PR #166223)

[Ryotaro Kasuga via llvm-commits]

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@@ -512,3 +528,45 @@ for.body:                                         ; preds = %entry, %for.body
 for.end:                                          ; preds = %for.body
   ret void
 }
+
+
+;;  for (long unsigned i = 0; i < 9223372036854775806; i++)
+;;    for (long unsigned j = 0; j < 2147483640; j++)
+;;      if (i < 3000000000)
+;;        A[i] = 0;
+;
+; FIXME: DependenceAnalysis fails to detect the dependency between A[i] and
+; itself, while Strong SIV has been able to prove it.
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kasuga-fj wrote:

> In general you are correct. If a test returns false it just mean that it couldn't prove anything. But in this case it is different. Sometime when StrongSIV is providing a distance or direction, it actually means that StrongSIV has been able to prove a dependency by providing their difference or direction. More specifically, whenever we have `StrongSIVsuccesses++` in the StrongSIV test, it means that the test could successfully prove (returning false) or disprove a dependency (returning true).
> 
> This is something I had mentioned before on another discussion. When StrongSIV is successful to prove a dependency, DA does not need to check other tests anymore.

Hmm, I've reconsidered things a bit and now this looks reasonable to me. But...

> FIXME: DependenceAnalysis fails to detect the dependency between A[i] and itself, and Strong SIV is not the reason of this failure.

I'd prefer this one.

https://github.com/llvm/llvm-project/pull/166223