-Wuninitialized warning on empty struct

[hjl-tools]

Bugzilla Link	26468
Version	trunk
OS	Linux

Extended Description

[hjl@gnu-6 empty-2]$ cat x.c
struct empty {};

struct empty
foo (void)
{
struct empty s;
return s;
}
[hjl@gnu-6 empty-2]$ make
/export/build/gnu/llvm-clang-bootstrap/stage1/build-x86_64-linux/bin/clang -m32 -S -O -Wall x.c
x.c:7:10: warning: variable 's' is uninitialized when used here
[-Wuninitialized]
return s;
^
x.c:6:3: note: variable 's' is declared here
struct empty s;
^
1 warning generated.
[hjl@gnu-6 empty-2]$

Shouldn't empty struct be a special case here?

[llvmbot]

@llvm/issue-subscribers-c

[AaronBallman]

We're also diagnosing the case where all the fields are unnamed bit-fields or zero-length bit-fields when we shouldn't be. GCC warns on none of:

struct One {};
struct Two { int : 0; };
struct Three { int : 12 };

https://godbolt.org/z/4E771zM5Y