Re: Undefined behavior detected by new clang's ubsan

As for the rest of the proposed fixes, most seem okay, but I have some nits:

Thank you for spending time on this!
I agree with all of your changes (except for one noted below) -- didn't
mean to propose committable changes, just wanted to show the fixes that
allowed check-world to pass.

heaptoast.c     memcpy(VARDATA(result) +
-         (curchunk * TOAST_MAX_CHUNK_SIZE - sliceoffset) + chcpystrt,
+         (int)(curchunk * TOAST_MAX_CHUNK_SIZE - sliceoffset) + chcpystrt,

Not sure about this one. It would be better if we reversing the
operands allowed us to avoid overflow in the first place:

-         (curchunk * TOAST_MAX_CHUNK_SIZE - sliceoffset) + chcpystrt,
+         chcpystrt + (curchunk * TOAST_MAX_CHUNK_SIZE - sliceoffset)

Does that silence the warning?

Unfortunately, no -- I still got:
heaptoast.c:771:17: runtime error: addition of unsigned offset to 0x78120673fac6 overflowed to 0x78120673fa04
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior heaptoast.c:771:17


Best regards,
Alexander