Implement -Wshift-op-parentheses for: a << b + c

This appears to be consistent with GCC's implementation of the same warning
under -Wparentheses. Suppressing a << b + c for cases where 'a' is a user
defined type for compatibility with C++ stream IO. Otherwise suggest
parentheses around the addition or subtraction subexpression.

(this came up when MSVC was complaining (incorrectly, so far as I can tell)
about a perceived violation of this within the LLVM codebase, PR14001)

llvm-svn: 165283

1 files changed, 21 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index bbae55b5980..d40818b83b0 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -8570,6 +8570,20 @@ static void DiagnoseBitwiseAndInBitwiseOr(Sema &S, SourceLocation OpLoc,
   }
 }
 
+static void DiagnoseAdditionInShift(Sema &S, SourceLocation OpLoc,
+                                    Expr *SubExpr, StringRef shift) {
+  if (BinaryOperator *Bop = dyn_cast<BinaryOperator>(SubExpr)) {
+    if (Bop->getOpcode() == BO_Add || Bop->getOpcode() == BO_Sub) {
+      StringRef op = Bop->getOpcode() == BO_Add ? "+" : "-";
+      S.Diag(Bop->getOperatorLoc(), diag::warn_addition_in_bitshift)
+          << Bop->getSourceRange() << OpLoc << op << shift;
+      SuggestParentheses(S, Bop->getOperatorLoc(),
+          S.PDiag(diag::note_addition_in_bitshift_silence) << op,
+          Bop->getSourceRange());
+    }
+  }
+}
+
 /// DiagnoseBinOpPrecedence - Emit warnings for expressions with tricky
 /// precedence.
 static void DiagnoseBinOpPrecedence(Sema &Self, BinaryOperatorKind Opc,
@@ -8591,6 +8605,13 @@ static void DiagnoseBinOpPrecedence(Sema &Self, BinaryOperatorKind Opc,
     DiagnoseLogicalAndInLogicalOrLHS(Self, OpLoc, LHSExpr, RHSExpr);
     DiagnoseLogicalAndInLogicalOrRHS(Self, OpLoc, LHSExpr, RHSExpr);
   }
+
+  if ((Opc == BO_Shl && LHSExpr->getType()->isIntegralType(Self.getASTContext()))
+      || Opc == BO_Shr) {
+    StringRef shift = Opc == BO_Shl ? "<<" : ">>";
+    DiagnoseAdditionInShift(Self, OpLoc, LHSExpr, shift);
+    DiagnoseAdditionInShift(Self, OpLoc, RHSExpr, shift);
+  }
 }
 
 // Binary Operators.  'Tok' is the token for the operator.