[clang] [clang][CodeGen] Fix shift-exponent ubsan check for signed _BitInt (PR #88004)

[Björn Pettersson via cfe-commits]

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@@ -146,6 +146,15 @@ struct BinOpInfo {
       return UnOp->getSubExpr()->getType()->isFixedPointType();
     return false;
   }
+
+  /// Check if the RHS has a signed integer representation.
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bjope wrote:

This is a Doxygen style comment (like the ones for other functions above). So there should be three '/'.

https://github.com/llvm/llvm-project/pull/88004