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.

/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

Fixes: #61960

Reviewed By: donat.nagy

Full diff: https://github.com/llvm/llvm-project/pull/65887.diff

2 Files Affected:

• (modified) clang/lib/StaticAnalyzer/Core/SValBuilder.cpp (+6)
• (added) clang/test/Analysis/bitint-no-crash.c (+11)

diff --git a/clang/lib/StaticAnalyzer/Core/SValBuilder.cpp b/clang/lib/StaticAnalyzer/Core/SValBuilder.cpp
index 4fe828bdf7681fc..c9765e3a653e30a 100644
--- a/clang/lib/StaticAnalyzer/Core/SValBuilder.cpp
+++ b/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(),
diff --git a/clang/test/Analysis/bitint-no-crash.c b/clang/test/Analysis/bitint-no-crash.c
new file mode 100644
index 000000000000000..6fa041974a3c981
--- /dev/null
+++ b/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;
+}