[PATCH] D151148: [clang][ExprConstant] fix __builtin_object_size for compound literal

[Eli Friedman via Phabricator via cfe-commits]

efriedma added inline comments.


================
Comment at: clang/lib/AST/ExprConstant.cpp:11737
     bool Ret = HandleSizeof(Info, ExprLoc, Ty, Result);
     if (Ty->isStructureType() &&
         Ty->getAsStructureType()->getDecl()->hasFlexibleArrayMember()) {
----------------
nickdesaulniers wrote:
> efriedma wrote:
> > For the second call to CheckHandleSizeof (line 11791), is the type of consistent with the type of the variable?  If Ty refers to a field, I'm not sure it makes sense to call getFlexibleArrayInitChars().  Something along the lines of "struct Z { struct A { int x, y[]; } z; int a; };"
> Can such an object even be initialized?
> ```
> cat /tmp/x.c
> struct Z { struct A { int x, y[]; } z; int a; };
> 
> static struct Z my_z = {
>   .z = {
>     .x = 42,
>     .y = {
>       0, 1, 2,
>     },
>   },
>   .a = 42,
> };
> 
> unsigned long foo (void) {
>   return __builtin_object_size(&my_z, 1);
> }
> $ clang -O2 /tmp/x.c -S -o -
> /tmp/x.c:1:37: warning: field 'z' with variable sized type 'struct A' not at the end of a struct or class is a GNU extension [-Wgnu-variable-sized-type-not-at-end]
> struct Z { struct A { int x, y[]; } z; int a; };
>                                     ^
> /tmp/x.c:6:10: error: initialization of flexible array member is not allowed
>     .y = {
>          ^
> /tmp/x.c:1:30: note: initialized flexible array member 'y' is here
> struct Z { struct A { int x, y[]; } z; int a; };
>                              ^
> 1 warning and 1 error generated.
> ```
> or did you have something else in mind?
I was thinking something more along the lines of

```
struct Z { struct A { int x, y[]; } z; int a; int b[]; };

static struct Z my_z = { .b = {1,2,3} };

unsigned long foo (void) {
  return __builtin_object_size(&my_z.z, 1);
}
```

The idea being that you're adding the length of the flexible member even though the caller isn't trying to ask about it.


Repository:
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  https://reviews.llvm.org/D151148/new/

https://reviews.llvm.org/D151148