Suppress all -Wunused-value warnings from macro body expansions.

This is inspired by a number of false positives in real code, including
PR14968. I've added test cases reduced from these false positives to
test/Sema/unused-expr.c, as well as corresponding test cases that pass the
offending expressions as arguments to a no-op macro to ensure that we do warn
there.

This also removes my previous tweak from r166522/r166534, so that we warn on
unused cast expressions in macro arguments.

There were several test cases that were using -Wunused-value to test general
diagnostic emission features; I changed those to use other warnings or warn on
a macro argument expression. I stared at the test case for PR14399 for a while
with Richard Smith and we believe the new test case exercises the same
codepaths as before.

llvm-svn: 172696

1 files changed, 20 insertions, 3 deletions

diff --git a/clang/test/Sema/unused-expr.c b/clang/test/Sema/unused-expr.c
index aa81febdbbd..0786ede6763 100644
--- a/clang/test/Sema/unused-expr.c
+++ b/clang/test/Sema/unused-expr.c
@@ -123,13 +123,30 @@ void f(int i, ...) {
 // PR8371
 int fn5() __attribute__ ((__const));
 
-// OpenSSL has some macros like this; we shouldn't warn on the cast.
+// Don't warn for unused expressions in macro bodies; however, do warn for
+// unused expressions in macro arguments. Macros below are reduced from code
+// found in the wild.
+#define NOP(a) (a)
 #define M1(a, b) (long)foo((a), (b))
-// But, we should still warn on other subexpressions of casts in macros.
 #define M2 (long)0;
+#define M3(a) (t3(a), fn2())
+#define M4(a, b) (foo((a), (b)) ? 0 : t3(a), 1)
+#define M5(a, b) (foo((a), (b)), 1)
 void t11(int i, int j) {
   M1(i, j);  // no warning
-  M2;  // expected-warning {{expression result unused}}
+  NOP((long)foo(i, j)); // expected-warning {{expression result unused}}
+  M2;  // no warning
+  NOP((long)0); // expected-warning {{expression result unused}}
+  M3(i); // no warning
+  NOP((t3(i), fn2())); // expected-warning {{ignoring return value}}
+  M4(i, j); // no warning
+  NOP((foo(i, j) ? 0 : t3(i), 1)); // expected-warning {{expression result unused}}
+  M5(i, j); // no warning
+  NOP((foo(i, j), 1)); // expected-warning {{expression result unused}}
 }
+#undef NOP
 #undef M1
 #undef M2
+#undef M3
+#undef M4
+#undef M5