Don't emit 'dead initialization' warnings for variables marked 'unused'.

This fixes PR 2573: http://llvm.org/bugs/show_bug.cgi?id=2573


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@54009 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/CheckDeadStores.cpp

@@ -164,11 +164,16 @@ public:
       for (ScopedDecl* SD = DS->getDecl(); SD; SD = SD->getNextDeclarator()) {
         
         VarDecl* V = dyn_cast<VarDecl>(SD);
-        if (!V) continue;
+
+        if (!V)
+          continue;
         
         if (V->hasLocalStorage())
-          if (Expr* E = V->getInit())
-            if (!Live(V, AD)) {
+          if (Expr* E = V->getInit()) {
+            // A dead initialization is a variable that is dead after it
+            // is initialized.  We don't flag warnings for those variables
+            // marked 'unused'.
+            if (!Live(V, AD) && V->getAttr<UnusedAttr>() == 0) {
               // Special case: check for initializations with constants.
               //
               //  e.g. : int x = 0;
@@ -179,6 +184,7 @@ public:
               if (!E->isConstantExpr(Ctx,NULL))
                 Report(V, DeadInit, V->getLocation(), E->getSourceRange());
             }
+          }
       }
   }
 };

test/Analysis/dead-stores.c

@@ -77,5 +77,12 @@ int f11() {
   return ++x; // expected-warning{{never read}}
 }
 
-
+int f12a(int y) {
+  int x = y;  // expected-warning{{never read}}
+  return 1;
+}
+int f12b(int y) {
+  int x __attribute__((unused)) = y;  // no-warning
+  return 1;
+}