[PATCH] D135920: [clang][Sema] Use correct array size for diagnostic

[Bill Wendling via Phabricator via cfe-commits]

void added inline comments.


================
Comment at: clang/test/SemaCXX/array-bounds.cpp:240
 
-    ((char*)foo)[sizeof(foo)] = '\0';  // expected-warning {{array index 32768 is past the end of the array (which contains 32768 elements)}}
+    ((char*)foo)[sizeof(foo)] = '\0';  // expected-warning {{array index 32768 is past the end of the array (which contains 4096 elements)}}
 
----------------
aaron.ballman wrote:
> void wrote:
> > serge-sans-paille wrote:
> > > kees wrote:
> > > > serge-sans-paille wrote:
> > > > > I find this new message quite confusing, because the array index is given in terms of char elements, while the array size is given in terms of double elements. I actually find the original message more consistent to that respect.
> > > > Perhaps show both element count and byte offset?
> > > > 
> > > > `array index $count is $(bytes - end_of_array_in_bytes) past the end of the array (which contains $end_of_array_in_bytes bytes of $array_max_index elements)`
> > > if we have no cast, I find the version without the patch  just fine.
> > > 
> > > If we have a cast, I suggest we just express the result in bytes, something along those lines (inspired by your suggestion):
> > > 
> > >     array index $count is $(bytes - end_of_array_in_bytes) bytes past the end of the allocated memory for that array (which contains $end_of_array_in_bytes bytes)
> > I so far have this. It looks not too bad even for the non-cast. Thoughts?
> > 
> > ```
> > $ cat ab.c
> > void test_pr10771() {
> >     double foo[4096];  // expected-note {{array 'foo' declared here}}
> > 
> >     ((char*)foo)[sizeof(foo)] = '\0';  // expected-warning {{array index 32768 is past the end of the array (which contains 4096 elements of type 'double[4096])}}
> >     foo[4098] = '\0';  // expected-warning {{array index 32768 is past the end of the array (which contains 4096 elements of type 'double[4096])}}
> > }
> > $ clang++ -x c++ -o /dev/null -S -std=c++14 ~/llvm/ab.c
> > /home/morbo/llvm/ab.c:4:13: warning: array index 32768 is 0 bytes past the end of the array (that has type 'double[4096]') [-Warray-bounds]
> >     ((char*)foo)[sizeof(foo)] = '\0';  // expected-warning {{array index 32768 is past the end of the array (which contains 4096 elements of type 'double[4096])}}
> >             ^    ~~~~~~~~~~~
> > /home/morbo/llvm/ab.c:2:5: note: array 'foo' declared here
> >     double foo[4096];  // expected-note {{array 'foo' declared here}}
> >     ^
> > /home/morbo/llvm/ab.c:5:5: warning: array index 4098 is 16 bytes past the end of the array (that has type 'double[4096]') [-Warray-bounds]
> >     foo[4098] = '\0';  // expected-warning {{array index 32768 is past the end of the array (which contains 4096 elements of type 'double[4096])}}
> >     ^   ~~~~
> > /home/morbo/llvm/ab.c:2:5: note: array 'foo' declared here
> >     double foo[4096];  // expected-note {{array 'foo' declared here}}
> >     ^
> > 2 warnings generated.
> > ```
> The part I struggle with is the "is 0 bytes past the end of the array" -- that reads as if it's not past the end of the array at all because it's saying "You've accessed right up to the end of the array; congratulations on your very careful use!".
Okay. How about this then?

```
Typical diagnostic:

  warning: array index %{index} is past the end of the array (that has type %{type})

Diagnostic if the array is cast to something else:

  warning: array index %{index} is past the end of the array (that has type %{type}, cast to ${cast_type})
```


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D135920/new/

https://reviews.llvm.org/D135920