From ce0e3f8a0920b72703b13a032a1809fae65423ee Mon Sep 17 00:00:00 2001
From: Ted Kremenek <kremenek@apple.com>
Date: Thu, 9 Jan 2014 20:19:45 +0000
Subject: [PATCH] Have attribute 'objc_precise_lifetime' suppress -Wunused.

Fixes <rdar://problem/15596883>

In ARC, __attribute__((objc_precise_lifetime)) guarantees that the
object stored in it will survive to the end of the variable's formal
lifetime.  It is therefore useful even if it completely unused.

llvm-svn: 198888
---
 clang/lib/Sema/SemaDecl.cpp  | 3 ++-
 clang/test/SemaObjC/unused.m | 9 +++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index fb041ed..78ead1e 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -1268,7 +1268,8 @@ static bool ShouldDiagnoseUnusedDecl(const NamedDecl *D) {
   if (D->isInvalidDecl())
     return false;
 
-  if (D->isReferenced() || D->isUsed() || D->hasAttr<UnusedAttr>())
+  if (D->isReferenced() || D->isUsed() || D->hasAttr<UnusedAttr>() ||
+      D->hasAttr<ObjCPreciseLifetimeAttr>())
     return false;
 
   if (isa<LabelDecl>(D))
diff --git a/clang/test/SemaObjC/unused.m b/clang/test/SemaObjC/unused.m
index 3fd1cf0..16a3899 100644
--- a/clang/test/SemaObjC/unused.m
+++ b/clang/test/SemaObjC/unused.m
@@ -72,3 +72,12 @@ static NSString *x = @"hi"; // expected-warning {{unused variable 'x'}}
 - (void) b {}
 - (void) a { [self b]; }
 @end
+
+// Test that objc_precise_lifetime suppresses
+// unused variable warnings.
+extern void rdar15596883_foo(void);
+void rdar15596883(id x) {
+  __attribute__((objc_precise_lifetime)) id y = x; // no-warning
+  rdar15596883_foo();
+}
+
-- 
2.7.4