fix PR4633: cast to void should silence the 'unused expression' warning.

llvm-svn: 77344

clang/lib/AST/Expr.cpp

@@ -593,11 +593,10 @@ bool Expr::isUnusedResultAWarning(SourceLocation &Loc, SourceRange &R1,
     return true;
   }
   case CStyleCastExprClass:
-    // If this is a cast to void, check the operand.  Otherwise, the result of
-    // the cast is unused.
+    // If this is an explicit cast to void, allow it.  People do this when they
+    // think they know what they're doing :).
     if (getType()->isVoidType())
-      return cast<CastExpr>(this)->getSubExpr()
-               ->isUnusedResultAWarning(Loc, R1, R2);
+      return false;
     Loc = cast<CStyleCastExpr>(this)->getLParenLoc();
     R1 = cast<CStyleCastExpr>(this)->getSubExpr()->getSourceRange();
     return true;

clang/test/Sema/unused-expr.c

@@ -43,4 +43,11 @@ void nowarn(unsigned char* a, unsigned char* b)
 {
   unsigned char c = 1;
   *a |= c, *b += c;
+
+
+  // PR4633
+  int y, x;
+  ((void)0), y = x;
 }
+
+