[clang] [Clang][CodeGen] Check `isUnderlyingBasePointerConstantNull` in `emitPointerArithmetic` (PR #137849)

[Yingwei Zheng via cfe-commits]

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@@ -4238,7 +4238,8 @@ static Value *emitPointerArithmetic(CodeGenFunction &CGF,
   else
     elemTy = CGF.ConvertTypeForMem(elementType);
 
-  if (CGF.getLangOpts().PointerOverflowDefined)
+  if (CGF.getLangOpts().PointerOverflowDefined ||
+      CGF.isUnderlyingBasePointerConstantNull(pointerOperand))
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dtcxzyw wrote:

`BinaryOperator::isNullPointerArithmeticExtension` only allows the pointer operand to be a constant null. But `isUnderlyingBasePointerConstantNull` also catches `((struct S*)0)->field`.
I think it is safe to remove this workaround and fall through to the `isUnderlyingBasePointerConstantNull` check.


https://github.com/llvm/llvm-project/pull/137849