[llvm] [InferAddressSpaces] apply InferAddressSpaces to inttoptr-zext-ptrtoint address expression. (PR #79108)

[via llvm-commits]

yujc9 wrote:

The reason for implementing this patch is to eliminate the cast for the pattern inttoptr - zext - ptrtoint. 
```
define void @zext_ptrint_conversion(ptr addrspace(3) %x) {
  %tmp1 = ptrtoint ptr addrspace(3) %x to i32
  %tmp2 = zext i32 %tmp1 to i64
  %tmp3 = inttoptr i64 %tmp2 to ptr
  store i32 0, ptr %tmp3
  ret void
}
```
For instance, if we try to store a value to a generic pointer `%tmp3` which is converted from a pointer `%x` with address space 3. If these two pointers have different size, an `zext` operation may be inserted. Since `zext` does not introduce any information, storing a value to the generic pointer `%tmp3` should be equivalent to storing to ptr addrspace(3) `%x` directly.
To keep the transformation safe, the `ptrtoint` and `inttoptr` operation should be no-op cast. In addition, we require these two pointers in different address spaces and different size so that no extra information is added by `zext` operation.
Not sure other possibilities to make this conversion unsafe.

https://github.com/llvm/llvm-project/pull/79108