[PATCH] D158069: [clang][Interp] Fix getIndex() for composite array elements

[Timm Bäder via Phabricator via cfe-commits]

tbaeder added inline comments.


================
Comment at: clang/lib/AST/Interp/Context.h:88
+  /// Returns the program. This is only needed for unittests.
+  Program &getProgram() const { return *P.get(); }
+
----------------
cor3ntin wrote:
> This should return a const ref
Things like `getGlobal()` aren't const so that doesn't work.


================
Comment at: clang/lib/AST/Interp/Pointer.h:342
+
+    // narrow()ed element in a composite array.
+    if (Base > 0 && Base == Offset)
----------------
cor3ntin wrote:
> Can you be a bit more verbose here? I can't figure out what is happening from the comment!
For primitive arrays, the elements don't have inline descriptors:

```
                     Offset
                     │
                     ▼
┌────────┬───┬───┬───┬───┬───┬─────┐
│InitMap │ 1 │ 2 │ 3 │ 4 │ 5 │ ... │
└────────┴───┴───┴───┴───┴───┴─────┘
▲
│
Base
```

If the array elements are composite elements themselves however, we can have a pointer that refers to the array element:

```
               Offset
               │
               ▼
┌──────────┬───┬──────────┬───┐
│InlineDesc│'a'│InlineDesc│'b'│
└──────────┴───┴──────────┴───┘
▲
│
Base
```

(so things like `isArrayElement()` return `true`) as well as a pointer that _only_ refers to the composite element (after a call to `narrow()`:

```
               Offset
               │
               ▼
┌──────────┬───┬──────────┬───┐
│InlineDesc│'a'│InlineDesc│'b'│
└──────────┴───┴──────────┴───┘
               ▲
               │
               Base
```

For the latter, the expected value of `getIndex()` is `0`, since it is (as far as the pointer knows) _not_ an array element.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D158069/new/

https://reviews.llvm.org/D158069