[PATCH] D77611: [Sema] fix -Wunused-result in StmtExpr

[David Blaikie via Phabricator via cfe-commits]

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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