[clang] [analyzer] Implement potential underflow warnings (PR #216077)

[Donát Nagy via cfe-commits]

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@@ -492,8 +491,7 @@ void ArrayBoundChecker::handleAccessExpr(const Expr *E,
         if (isTainted(State, ASE->getIdx(), C.getStackFrame()))
           OffsetName = "index";
 
-      BugDescription Desc =
-          describeTaintBug(RegName, OffsetName, Res.mayUnderflow());
+      BugDescription Desc = describeTaintBug(Res, RegName, OffsetName);
       reportOOB(C, State, Desc, ByteOffset, Extent, /*IsTaintBug=*/true);
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NagyDonat wrote:

Good point, corrected the behavior and added your regression test in https://github.com/llvm/llvm-project/pull/216077/commits/1d865c792e9b7a4663c7cc1c861aa1d50a1db0aa

By the way, IIRC something like this was already implemented in one of the earlier versions of the "split out the bounds checking library" change, but it was lost in the back and forth changes.

https://github.com/llvm/llvm-project/pull/216077