[analyzer] Fix crash analyzing _BitInt() in evalIntegralCast (llvm#65887)

evalIntegralCast was using makeIntVal, and when _BitInt() types were
introduced this exposed a crash in evalIntegralCast as a result.

Improve evalIntegralCast to use makeIntVal more efficiently to avoid the
crash exposed by use of _BitInt.

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

...
 llvm#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#61960

 Reviewed By: donat.nagy

Author: vabridgers

clang/lib/StaticAnalyzer/Core/SValBuilder.cpp

@@ -598,11 +598,9 @@ SVal SValBuilder::evalIntegralCast(ProgramStateRef state, SVal val,
   APSIntType ToType(getContext().getTypeSize(castTy),
                     castTy->isUnsignedIntegerType());
   llvm::APSInt ToTypeMax = ToType.getMaxValue();
-  NonLoc ToTypeMaxVal =
-      makeIntVal(ToTypeMax.isUnsigned() ? ToTypeMax.getZExtValue()
-                                        : ToTypeMax.getSExtValue(),
-                 castTy)
-          .castAs<NonLoc>();
+
+  NonLoc ToTypeMaxVal = makeIntVal(ToTypeMax);
+
   // Check the range of the symbol being casted against the maximum value of the
   // target type.
   NonLoc FromVal = val.castAs<NonLoc>();

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;
+}