[analyzer] Do not use APInt methods on _BitInt() Types

evalIntegralCast is using APInt method to get the value of _BitInt()
values after _BitInt() changes were introduced. Some of those methods
assume values are less than or equal to 64-bits, which is not true for
_BitInt() types. This change simply side steps that issue if the
_BitInt() type is greater than 64 bits.

This was caught with our internal randomized testing.

<src-root>/llvm/include/llvm/ADT/APInt.h:1510:
  int64_t llvm::APInt::getSExtValue() const: Assertion
  `getSignificantBits() <= 64 && "Too many bits for int64_t"' failed.a

...
 #9 <address> llvm::APInt::getSExtValue() const
  <src-root>/llvm/include/llvm/ADT/APInt.h:1510:5
  llvm::IntrusiveRefCntPtr<clang::ento::ProgramState const>,
  clang::ento::SVal, clang::QualType, clang::QualType)
  <src-root>/clang/lib/StaticAnalyzer/Core/SValBuilder.cpp:607:24
  clang::Expr const*, clang::ento::ExplodedNode*, clang::ento::ExplodedNodeSet&)
  <src-root>/clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp:413:61
...

 Fixes: llvm/llvm-project#61960

 Reviewed By: donat.nagy

Author: vabridgers

clang/lib/StaticAnalyzer/Core/SValBuilder.cpp

@@ -598,6 +598,12 @@ SVal SValBuilder::evalIntegralCast(ProgramStateRef state, SVal val,
   APSIntType ToType(getContext().getTypeSize(castTy),
                     castTy->isUnsignedIntegerType());
   llvm::APSInt ToTypeMax = ToType.getMaxValue();
+  // With the introduction of _BitInt(), integral types can be
+  // > 64 bits. So check for this and skip the size checks
+  // falling back to making a non loc return type.
+  if (ToTypeMax.getSignificantBits() > 64) {
+    return makeNonLoc(se, originalTy, castTy);
+  }
   NonLoc ToTypeMaxVal =
       makeIntVal(ToTypeMax.isUnsigned() ? ToTypeMax.getZExtValue()
                                         : ToTypeMax.getSExtValue(),

clang/test/Analysis/bitint-no-crash.c

@@ -0,0 +1,11 @@
+ // RUN: %clang_analyze_cc1 -analyzer-checker=core \
+ // RUN:   -analyzer-checker=debug.ExprInspection \
+ // RUN:   -verify %s
+
+// Don't crash when using _BitInt()
+// expected-no-diagnostics
+_BitInt(256) a;
+_BitInt(129) b;
+void c() {
+  b = a;
+}