[clang] [clang][analyzer] Correct SMT Layer for _BitInt cases refutations (PR #143310)

[Donát Nagy via cfe-commits]

================
@@ -570,23 +572,42 @@ class SMTConv {
   // TODO: Refactor to put elsewhere
   static inline QualType getAPSIntType(ASTContext &Ctx,
                                        const llvm::APSInt &Int) {
-    return Ctx.getIntTypeForBitwidth(Int.getBitWidth(), Int.isSigned());
+    QualType Ty = Ctx.getIntTypeForBitwidth(Int.getBitWidth(), Int.isSigned());
+    // If Ty is Null, could be because the original type was a _BitInt.
+    // Get the bit size and round up to next power of 2, max char size
+    if (Ty.isNull()) {
+      unsigned CharTypeSize = Ctx.getTypeSize(Ctx.CharTy);
+      unsigned pow2DestWidth =
+          std::max(llvm::bit_ceil(Int.getBitWidth()), CharTypeSize);
+      Ty = Ctx.getIntTypeForBitwidth(pow2DestWidth, Int.isSigned());
----------------
NagyDonat wrote:

```suggestion
      unsigned Pow2DestWidth =
          std::max(llvm::bit_ceil(Int.getBitWidth()), CharTypeSize);
      Ty = Ctx.getIntTypeForBitwidth(Pow2DestWidth, Int.isSigned());
```
Please follow the [LLVM Coding Standard](https://www.llvm.org/docs/CodingStandards.html#name-types-functions-variables-and-enumerators-properly).

https://github.com/llvm/llvm-project/pull/143310