don't warn about unused values when the unused value is a statement expression expanded from a macro. This is of dubious utility in general, but is specifically a major issue for the linux kernel. This resolves PR13747.

llvm-svn: 163034

1 files changed, 7 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index c885d484e71..76410e20aca 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -160,6 +160,13 @@ void Sema::DiagnoseUnusedExprResult(const Stmt *S) {
       !E->isUnusedResultAWarning(WarnExpr, Loc, R1, R2, Context))
     return;
 
+  // If this is a GNU statement expression expanded from a macro, it is probably
+  // unused because it is a function-like macro that can be used as either an
+  // expression or statement.  Don't warn, because it is almost certainly a
+  // false positive.
+  if (isa<StmtExpr>(E) && Loc.isMacroID())
+    return;
+
   // Okay, we have an unused result.  Depending on what the base expression is,
   // we might want to make a more specific diagnostic.  Check for one of these
   // cases now.