Add a warning to diagnose statements in C++ like "*(volatile int*)x;". Conceptually, this is part of -Wunused-value, but I added a separate flag -Wunused-volatile-lvalue so it doesn't get turned off by accident with -Wno-unused-value. I also made a few minor improvements to existing unused value warnings in the process. <rdar://problem/11516811>.

llvm-svn: 157362

2 files changed, 10 insertions, 4 deletions

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 67b60fad519..ce4234b7b06 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -7412,8 +7412,6 @@ QualType Sema::CheckAssignmentOperands(Expr *LHSExpr, ExprResult &RHS,
 // C99 6.5.17
 static QualType CheckCommaOperands(Sema &S, ExprResult &LHS, ExprResult &RHS,
                                    SourceLocation Loc) {
-  S.DiagnoseUnusedExprResult(LHS.get());
-
   LHS = S.CheckPlaceholderExpr(LHS.take());
   RHS = S.CheckPlaceholderExpr(RHS.take());
   if (LHS.isInvalid() || RHS.isInvalid())
@@ -7429,6 +7427,8 @@ static QualType CheckCommaOperands(Sema &S, ExprResult &LHS, ExprResult &RHS,
   if (LHS.isInvalid())
     return QualType();
 
+  S.DiagnoseUnusedExprResult(LHS.get());
+
   if (!S.getLangOpts().CPlusPlus) {
     RHS = S.DefaultFunctionArrayLvalueConversion(RHS.take());
     if (RHS.isInvalid())
diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index f64fc96c0ec..a342cbd6cc1 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -153,10 +153,11 @@ void Sema::DiagnoseUnusedExprResult(const Stmt *S) {
   if (!E)
     return;
 
+  const Expr *WarnExpr;
   SourceLocation Loc;
   SourceRange R1, R2;
   if (SourceMgr.isInSystemMacro(E->getExprLoc()) ||
-      !E->isUnusedResultAWarning(Loc, R1, R2, Context))
+      !E->isUnusedResultAWarning(WarnExpr, Loc, R1, R2, Context))
     return;
 
   // Okay, we have an unused result.  Depending on what the base expression is,
@@ -171,7 +172,7 @@ void Sema::DiagnoseUnusedExprResult(const Stmt *S) {
   if (DiagnoseUnusedComparison(*this, E))
     return;
 
-  E = E->IgnoreParenImpCasts();
+  E = WarnExpr;
   if (const CallExpr *CE = dyn_cast<CallExpr>(E)) {
     if (E->getType()->isVoidType())
       return;
@@ -229,6 +230,11 @@ void Sema::DiagnoseUnusedExprResult(const Stmt *S) {
     }
   }
 
+  if (E->isGLValue() && E->getType().isVolatileQualified()) {
+    Diag(Loc, diag::warn_unused_volatile) << R1 << R2;
+    return;
+  }
+
   DiagRuntimeBehavior(Loc, 0, PDiag(DiagID) << R1 << R2);
 }