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

[Balazs Benics via cfe-commits]

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@@ -250,6 +250,19 @@ BasicValueFactory::evalAPSInt(BinaryOperator::Opcode Op, const llvm::APSInt &V1,
       llvm_unreachable("Invalid Opcode.");
 
     case BO_Mul:
+      // For large bit widths (like __int128), check for potential crashes
+      if (V1.getBitWidth() >= 128 || V2.getBitWidth() >= 128) {
+        // If either operand is zero, result is zero
+        if (V1 == 0 || V2 == 0) {
+          return getValue(llvm::APSInt(llvm::APInt::getZero(std::max(V1.getBitWidth(), V2.getBitWidth())),
+                                       V1.isUnsigned() && V2.isUnsigned()));
+        }
+
+        // For __int128 types, be conservative to avoid crashes in APInt multiplication
+        // This happens when multiplying unsigned __int128 with large values (like negative
+        // numbers converted to unsigned)
+        return std::nullopt;
+      }
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steakhal wrote:

This code does not seem convincing.
In theory, we should be able to evaluate a multiplication here regardless of the bitwidths.
Is there some safe APSInt operation that does this?
And what about the rest of the operations, like `BO_Div` and friends. There we would still crash if I understand this right.

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