[llvm] [SDAG] Introduce inbounds flag for ISD::PTRADD (PR #162477)

[Eli Friedman via llvm-commits]

https://github.com/efriedma-quic commented:

Probably the header should have a warning that this is implicitly an inttoptr of the "pointer" operand, so the set of optimizations that apply is restricted.  As we discussed in #131862, a lot of obvious optimizations don't work because it's hard to prove anything about the provenance of the pointer value.

Otherwise, I think this is reasonable.

https://github.com/llvm/llvm-project/pull/162477