kees added inline comments.
================ Comment at: clang/lib/CodeGen/CGExpr.cpp:906 // member, only a T[0] or T[] member gets that treatment. + // Under StrictFlexArraysLevel, obey c99+ that disallows FAM in union, see + // C11 6.7.2.1 ยง18 ---------------- jyknight wrote: > serge-sans-paille wrote: > > jyknight wrote: > > > I believe this bit is incorrect -- it should just go back to 'return > > > true;'. The StrictFlexArraysLevel check above already eliminates the > > > cases we want to eliminate (size==1 in strictness-level 2.) > > Well, if we are in strictness-level 2, with an undefined size or size = 0, > > we can still reach that path, and don't want to return 'true' because FAM > > in union are in invalid per the standard. > Yes, we can reach this path, which is why the change is incorrect. We should > not be changing the FAMness of undefined size, or size == 0, in any of the > modes. To be more specific -- > > `union X { int x[0]; };` should still be a FAM in all strictness modes. (if > you don't want zero-length-arrays, use `-Werror=zero-length-array`). > > For `union X { int x[]; };`: this ought to be a compiler error. It's likely > just an oversight that we currently accept it; I'd be OK with a (separate) > patch to fix that. (GCC emits an error, so there's unlikely to be > compatibility issues with such a change.) > `union X { int x[0]; };` should still be a FAM in all strictness modes. (if > you don't want zero-length-arrays, use `-Werror=zero-length-array`). The Linux kernel cannot use `-Wzero-length-array` because we have cases of userspace APIs being stuck with them. (i.e. they are part of the struct declaration, even though the kernel code doesn't use them.) For example: ``` In file included from ../kernel/bounds.c:13: In file included from ../include/linux/log2.h:12: In file included from ../include/linux/bitops.h:9: In file included from ../include/uapi/linux/kernel.h:5: ../include/uapi/linux/sysinfo.h:22:10: error: zero size arrays are an extension [-Werror,-Wzero-length-array] char _f[20-2*sizeof(__kernel_ulong_t)-sizeof(__u32)]; /* Padding: libc5 uses this.. */ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ``` Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D126864/new/ https://reviews.llvm.org/D126864 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits