make the diagnostic in the 'unused result' warning more precise

about the reason, rdar://7186119.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@83940 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 33 insertions, 13 deletions

diff --git a/lib/AST/Expr.cpp b/lib/AST/Expr.cpp
index 98348d6efc..6da11c1cab 100644
--- a/lib/AST/Expr.cpp
+++ b/lib/AST/Expr.cpp
@@ -692,21 +692,22 @@ bool Expr::isUnusedResultAWarning(SourceLocation &Loc, SourceRange &R1,
   case CXXMemberCallExprClass: {
     // If this is a direct call, get the callee.
     const CallExpr *CE = cast<CallExpr>(this);
-    const Expr *CalleeExpr = CE->getCallee()->IgnoreParenCasts();
-    if (const DeclRefExpr *CalleeDRE = dyn_cast<DeclRefExpr>(CalleeExpr)) {
+    if (const FunctionDecl *FD = CE->getDirectCallee()) {
       // If the callee has attribute pure, const, or warn_unused_result, warn
       // about it. void foo() { strlen("bar"); } should warn.
-      if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(CalleeDRE->getDecl()))
-        if (FD->getAttr<WarnUnusedResultAttr>() ||
-            FD->getAttr<PureAttr>() || FD->getAttr<ConstAttr>()) {
-          Loc = CE->getCallee()->getLocStart();
-          R1 = CE->getCallee()->getSourceRange();
-
-          if (unsigned NumArgs = CE->getNumArgs())
-            R2 = SourceRange(CE->getArg(0)->getLocStart(),
-                             CE->getArg(NumArgs-1)->getLocEnd());
-          return true;
-        }
+      //
+      // Note: If new cases are added here, DiagnoseUnusedExprResult should be
+      // updated to match for QoI.
+      if (FD->getAttr<WarnUnusedResultAttr>() ||
+          FD->getAttr<PureAttr>() || FD->getAttr<ConstAttr>()) {
+        Loc = CE->getCallee()->getLocStart();
+        R1 = CE->getCallee()->getSourceRange();
+
+        if (unsigned NumArgs = CE->getNumArgs())
+          R2 = SourceRange(CE->getArg(0)->getLocStart(),
+                           CE->getArg(NumArgs-1)->getLocEnd());
+        return true;
+      }
     }
     return false;
   }
diff --git a/lib/Sema/SemaStmt.cpp b/lib/Sema/SemaStmt.cpp
index 2a3b9eeea8..e8cd6b081d 100644
--- a/lib/Sema/SemaStmt.cpp
+++ b/lib/Sema/SemaStmt.cpp
@@ -80,6 +80,25 @@ void Sema::DiagnoseUnusedExprResult(const Stmt *S) {
   E = E->IgnoreParens();
   if (isa<ObjCImplicitSetterGetterRefExpr>(E))
     DiagID = diag::warn_unused_property_expr;
+  
+  if (const CallExpr *CE = dyn_cast<CallExpr>(E)) {
+    // If the callee has attribute pure, const, or warn_unused_result, warn with
+    // a more specific message to make it clear what is happening.
+    if (const FunctionDecl *FD = CE->getDirectCallee()) {
+      if (FD->getAttr<WarnUnusedResultAttr>()) {
+        Diag(Loc, diag::warn_unused_call) << R1 << R2 << "warn_unused_result";
+        return;
+      }
+      if (FD->getAttr<PureAttr>()) {
+        Diag(Loc, diag::warn_unused_call) << R1 << R2 << "pure";
+        return;
+      }
+      if (FD->getAttr<ConstAttr>()) {
+        Diag(Loc, diag::warn_unused_call) << R1 << R2 << "const";
+        return;
+      }
+    }        
+  }
 
   Diag(Loc, DiagID) << R1 << R2;
 }