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, 3 insertions, 2 deletions

diff --git a/clang/test/Preprocessor/pragma_microsoft.c b/clang/test/Preprocessor/pragma_microsoft.c
index 156d05243b1..c0ddf74340c 100644
--- a/clang/test/Preprocessor/pragma_microsoft.c
+++ b/clang/test/Preprocessor/pragma_microsoft.c
@@ -26,7 +26,7 @@ __pragma(comment(linker," bar=" BAR))
 #define MACRO_WITH__PRAGMA { \
   __pragma(warning(push)); \
   __pragma(warning(disable: 10000)); \
-  2+2; \
+  1 + (2 > 3) ? 4 : 5; \
   __pragma(warning(pop)); \
 }
 
@@ -36,7 +36,8 @@ void f()
 
   // If we ever actually *support* __pragma(warning(disable: x)),
   // this warning should go away.
-  MACRO_WITH__PRAGMA // expected-warning {{expression result unused}}
+  MACRO_WITH__PRAGMA // expected-warning {{lower precedence}} \
+                     // expected-note 2 {{place parentheses}}
 }