Add warning group -Woverloaded-shift-op-parentheses to -Wparentheses. This

will fire on code such as:

  cout << x == 0;

which the compiler will intrepret as

  (cout << x) == 0;

This warning comes with two fixits attached to notes, one for parentheses to
silence the warning, and another to evaluate the comparison first.

llvm-svn: 179662

1 files changed, 32 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index cdfdc09e06e..ce60f9171fd 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -8877,6 +8877,33 @@ static void DiagnoseAdditionInShift(Sema &S, SourceLocation OpLoc,
   }
 }
 
+static void DiagnoseShiftCompare(Sema &S, SourceLocation OpLoc,
+                                 Expr *LHSExpr, Expr *RHSExpr) {
+  CXXOperatorCallExpr *OCE = dyn_cast<CXXOperatorCallExpr>(LHSExpr);
+  if (!OCE)
+    return;
+
+  FunctionDecl *FD = OCE->getDirectCallee();
+  if (!FD || !FD->isOverloadedOperator())
+    return;
+
+  OverloadedOperatorKind Kind = FD->getOverloadedOperator();
+  if (Kind != OO_LessLess && Kind != OO_GreaterGreater)
+    return;
+
+  S.Diag(OpLoc, diag::warn_overloaded_shift_in_comparison)
+      << LHSExpr->getSourceRange() << RHSExpr->getSourceRange()
+      << (Kind == OO_LessLess);
+  SuggestParentheses(S, OpLoc,
+                     S.PDiag(diag::note_evaluate_comparison_first),
+                     SourceRange(OCE->getArg(1)->getLocStart(),
+                                 RHSExpr->getLocEnd()));
+  SuggestParentheses(S, OCE->getOperatorLoc(),
+                     S.PDiag(diag::note_precedence_silence)
+                         << (Kind == OO_LessLess ? "<<" : ">>"),
+                     OCE->getSourceRange());
+}
+
 /// DiagnoseBinOpPrecedence - Emit warnings for expressions with tricky
 /// precedence.
 static void DiagnoseBinOpPrecedence(Sema &Self, BinaryOperatorKind Opc,
@@ -8905,6 +8932,11 @@ static void DiagnoseBinOpPrecedence(Sema &Self, BinaryOperatorKind Opc,
     DiagnoseAdditionInShift(Self, OpLoc, LHSExpr, Shift);
     DiagnoseAdditionInShift(Self, OpLoc, RHSExpr, Shift);
   }
+
+  // Warn on overloaded shift operators and comparisons, such as:
+  // cout << 5 == 4;
+  if (BinaryOperator::isComparisonOp(Opc))
+    DiagnoseShiftCompare(Self, OpLoc, LHSExpr, RHSExpr);
 }
 
 // Binary Operators.  'Tok' is the token for the operator.