[clang] [clang][StaticAnalyzer] Fix crash in SimpleSValBuilder with unsigned __int128 and negative literals (PR #150225)

[Balazs Benics via cfe-commits]

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@@ -164,6 +170,11 @@ BuiltinFunctionChecker::checkOverflow(CheckerContext &C, SVal RetVal,
   SVal IsLeMax = SVB.evalBinOp(State, BO_LE, RetVal, MaxVal, Res);
   SVal IsGeMin = SVB.evalBinOp(State, BO_GE, RetVal, MinVal, Res);
 
+  // If the comparison results are unknown, be conservative
+  if (IsLeMax.isUnknown() || IsGeMin.isUnknown()) {
+    return {true, true};
+  }
+
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steakhal wrote:

I thought that `assume(x,z)` is `{true,true}` if either of `x` or `y` are `Unknown`.
This would suggest to me that `{MayOverflow || MayUnderflow, MayNotOverflow && MayNotUnderflow}` should also result in `{true,true}` if `x` or `y` was `Unknown`.

WDYT?

// of course checking it before the `assume` should do no harm, it's just unnecessary.

https://github.com/llvm/llvm-project/pull/150225