dblaikie added a comment.
In D77611#1965824 <https://reviews.llvm.org/D77611#1965824>, @nickdesaulniers
wrote:
> ah, using this to build a Linux kernel triggers tons of warnings. So the
> behavior of GCC is even more subtle than captured in the test cases here.
At least one thing I noticed - GCC only warns about the first unused statement
in a statement expression (whether or not it's in a macro):
$ g++-tot warn.cpp -Wunused-value -c
In file included from warn.cpp:1:
warn.cpp: In function ‘int main()’:
warn.cpp:2:14: warning: statement has no effect [-Wunused-value]
2 | #define X ({ y; z; })
| ^
warn.cpp:6:15: note: in expansion of macro ‘X’
6 | assert(4 == X);
| ^
warn.cpp:7:3: warning: statement has no effect [-Wunused-value]
7 | y;
| ^
warn.cpp:8:3: warning: statement has no effect [-Wunused-value]
8 | z;
| ^
warn.cpp:9:4: warning: statement has no effect [-Wunused-value]
9 | ({ y; z; });
| ^
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