[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:

> while this case only drops the inbounds, but still keeps the gep null, resulting in a pointer with nullary provenance, so any loads/stores on it are UB.

Unfortunately, the result of `__PTR_ALIGN` will be used to perform memory access :(
https://github.com/gcc-mirror/gcc/blob/79aa2a283a8d3327ff4d6dca77e81d5b1ac3a01e/libiberty/obstack.c#L213-L218

So this workaround doesn't address the real issue...


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