[llvm] [DA] do not handle array accesses of different offsets (PR #123436)

[Sebastian Pop via llvm-commits]

sebpop wrote:

> I don't fully understand this component yet, but not sure if "the offset is `%N` and `%N % 4 == 0"` and "the offset is `4 * %n` where `%N == 4 * %n` are equivalent. For example, if we have the following IR
> 
> ```
> %arrayidx0 = getelementptr inbounds i8, ptr %A, i64 %N
> store i32 42, ptr %arrayidx0, align 1
> 
> %arrayidx1 = getelementptr inbounds i32, ptr %A, i64 %M
> store i32 42, ptr %arrayidx1, align 4
> ```

I added this as a testcase in 480ceff.

> 
> Under the assumption `%N % 4 == 0`, the former means like `A[N/4] = 42`, and the later is `A[M] = 42`. It seems that the current implementation doesn't perform such explicit division. 

DA sees the following access functions:
```
    subscript 0
	src = (%n + %A)
	dst = ((4 * %m)<nsw> + %A)
```
The compile time check for `4 * %m modulo 4 == 0` is trivial, only a runtime check for `%n modulo 4 == 0` is recorded. 


https://github.com/llvm/llvm-project/pull/123436