[llvm] [LV] Extend FindLastIV to unsigned case (PR #141752)

[Luke Lau via llvm-commits]

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@@ -843,66 +843,184 @@ exit:                                             ; preds = %for.body, %entry
 ; This test cannot be vectorized, even with a runtime check.
 ; The construct that are introduced by IndVarSimplify is:
 ;   %1 = trunc i64 %iv to i32
-; However, the loop exit condition is a constant that overflows i32:
+; The loop exit condition is a constant that overflows signed i32,
+; but not unsigned i32:
 ;   %exitcond.not = icmp eq i64 %inc, 4294967294
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lukel97 wrote:

Should we duplicate this test so we still have a negative test that overflows both signed and unsigned i32? It should also probably be moved out of the negative test section

https://github.com/llvm/llvm-project/pull/141752