r198888 - Have attribute 'objc_precise_lifetime' suppress -Wunused.

[Ted Kremenek]

Author: kremenek
Date: Thu Jan  9 14:19:45 2014
New Revision: 198888

URL: http://llvm.org/viewvc/llvm-project?rev=198888&view=rev
Log:
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.

Modified:
    cfe/trunk/lib/Sema/SemaDecl.cpp
    cfe/trunk/test/SemaObjC/unused.m

Modified: cfe/trunk/lib/Sema/SemaDecl.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDecl.cpp?rev=198888&r1=198887&r2=198888&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaDecl.cpp (original)
+++ cfe/trunk/lib/Sema/SemaDecl.cpp Thu Jan  9 14:19:45 2014
@@ -1268,7 +1268,8 @@ static bool ShouldDiagnoseUnusedDecl(con
   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))

Modified: cfe/trunk/test/SemaObjC/unused.m
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaObjC/unused.m?rev=198888&r1=198887&r2=198888&view=diff
==============================================================================
--- cfe/trunk/test/SemaObjC/unused.m (original)
+++ cfe/trunk/test/SemaObjC/unused.m Thu Jan  9 14:19:45 2014
@@ -72,3 +72,12 @@ static NSString *x = @"hi"; // expected-
 - (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();
+}
+