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.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172696 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 5 insertions, 2 deletions

diff --git a/lib/Sema/SemaStmt.cpp b/lib/Sema/SemaStmt.cpp
index db314fa50c..a2daa18d45 100644
--- a/lib/Sema/SemaStmt.cpp
+++ b/lib/Sema/SemaStmt.cpp
@@ -157,12 +157,15 @@ void Sema::DiagnoseUnusedExprResult(const Stmt *S) {
   const Expr *E = dyn_cast_or_null<Expr>(S);
   if (!E)
     return;
+  SourceLocation ExprLoc = E->IgnoreParens()->getExprLoc();
+  if (SourceMgr.isInSystemMacro(ExprLoc) ||
+      SourceMgr.isMacroBodyExpansion(ExprLoc))
+    return;
 
   const Expr *WarnExpr;
   SourceLocation Loc;
   SourceRange R1, R2;
-  if (SourceMgr.isInSystemMacro(E->getExprLoc()) ||
-      !E->isUnusedResultAWarning(WarnExpr, Loc, R1, R2, Context))
+  if (!E->isUnusedResultAWarning(WarnExpr, Loc, R1, R2, Context))
     return;
 
   // If this is a GNU statement expression expanded from a macro, it is probably