[InstCombine] Range check comparing alloca with non-aliasing ptr not eliminated

```llvm
define i1 @src(ptr %base, i64 %len) {
%2 = alloca i64, align 8
%12 = getelementptr inbounds i8, ptr %base, i64 %len
%13 = icmp uge ptr %2, %base
%14 = icmp ult ptr %2, %12
%15 = and i1 %13, %14
ret i1 %15
}

define i1 @tgt(ptr %base, i64 %len) {
ret i1 false
}
```

https://alive2.llvm.org/ce/z/u_8tT7

This pattern occurs very often with SmallVector, which on push_back of large (>16B) structs first checks whether the reference is inside the vector's storage, and is never eliminated. Probably something that InstCombine (or maybe even InstSimplify?) should eliminate.

Start with the InstCombine code path for pointer range comparisons and compare it with the possible InstSimplify path. Reproduce the LLVM IR example from the issue and use the linked Alive2 result as the behavioral reference; done means the check involving the alloca and non-aliasing pointer range is eliminated to false.

Written by the indexing model from the issue text.