[PATCH] D123649: Allow flexible array initialization in C++.

[Eli Friedman via Phabricator via cfe-commits]

efriedma added inline comments.


================
Comment at: clang/lib/CodeGen/CodeGenModule.cpp:4639
+          getDataLayout().getTypeAllocSize(Init->getType()));
+      assert(VarSize == CstSize && "Emitted constant has unexpected size");
+#endif
----------------
ahatanak wrote:
> efriedma wrote:
> > ahatanak wrote:
> > > This assertion fails when the following code is compiled:
> > > 
> > > 
> > > ```
> > > typedef unsigned char uint8_t;
> > > typedef uint8_t uint8_a16 __attribute__((aligned(16)));
> > > 
> > > void foo1() {
> > >   static const uint8_a16 array1[] = { 1 };
> > > }
> > > ```
> > `sizeof(uint8_a16[1])` is 16, but we currently emit a one-byte global.  So it seems like there's an underlying bug exposed by the assertion.
> > 
> > gcc thinks this is nonsense, and just prints an error.
> It seems to me that we should disallow arrays that have an element whose alignment is larger than its size, just as gcc does.
> 
> But I see arrays like that declared in a couple of clang's regression tests (e.g., `Sema/attr-aligned.c`). I'm not sure whether there was a reason for not rejecting it or it was just an oversight.
I'd guess oversight; it's originally a gcc extension, and using it to insert padding into arrays doesn't really make sense.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D123649/new/

https://reviews.llvm.org/D123649