[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());
+    }
+    return Ty;
+  }
+
+  static inline bool IsPower2(unsigned bits) {
+    return bits > 0 && (bits & (bits - 1)) == 0;
   }
 
   // Get the QualTy for the input APSInt, and fix it if it has a bitwidth of 1.
   static inline std::pair<llvm::APSInt, QualType>
   fixAPSInt(ASTContext &Ctx, const llvm::APSInt &Int) {
     llvm::APSInt NewInt;
+    unsigned APSIntBitwidth = Int.getBitWidth();
+    QualType Ty = getAPSIntType(Ctx, Int);
 
     // FIXME: This should be a cast from a 1-bit integer type to a boolean type,
     // but the former is not available in Clang. Instead, extend the APSInt
     // directly.
-    if (Int.getBitWidth() == 1 && getAPSIntType(Ctx, Int).isNull()) {
+    if (APSIntBitwidth == 1 && Ty.isNull()) {
       NewInt = Int.extend(Ctx.getTypeSize(Ctx.BoolTy));
+      Ty = getAPSIntType(Ctx, NewInt);
+    } else if (!IsPower2(APSIntBitwidth) && !getAPSIntType(Ctx, Int).isNull()) {
+      Ty = getAPSIntType(Ctx, Int);
----------------
NagyDonat wrote:

```suggestion
    } else if (!IsPower2(APSIntBitwidth) && !Ty.isNull()) {
```
You already introduce `Ty` above this.

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