[clang] [compiler-rt] [ubsan] Display correct runtime messages for negative _BitInt (PR #96240)

[Fangrui Song via cfe-commits]

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@@ -125,6 +137,26 @@ class TypeDescriptor {
     return 1 << (TypeInfo >> 1);
   }
 
+  const char *getBitIntBitCountPointer() const {
+    CHECK(isBitIntTy());
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MaskRay wrote:

CHECK unconditionally compiles to additional code. perhaps DCHECK 

https://github.com/llvm/llvm-project/pull/96240