[c++20] P1152R4: warn on any simple-assignment to a volatile lvalue

whose value is not ignored.

We don't warn on all the cases that are deprecated: specifically, we
choose to not warn for now if there are parentheses around the
assignment but its value is not actually used. This seems like a more
defensible rule, particularly for cases like sizeof(v = a), where the
parens are part of the operand rather than the sizeof syntax.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@374135 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 11 insertions, 0 deletions

diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index 9d1475d201..bcd059be91 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -6654,6 +6654,9 @@ def err_increment_decrement_enum : Error<
 def warn_deprecated_increment_decrement_volatile : Warning<
   "%select{decrement|increment}0 of object of volatile-qualified type %1 "
   "is deprecated">, InGroup<DeprecatedVolatile>;
+def warn_deprecated_simple_assign_volatile : Warning<
+  "use of result of assignment to object of volatile-qualified type %0 "
+  "is deprecated">, InGroup<DeprecatedVolatile>;
 def warn_deprecated_compound_assign_volatile : Warning<
   "compound assignment to object of volatile-qualified type %0 is deprecated">,
   InGroup<DeprecatedVolatile>;
diff --git a/include/clang/Sema/Sema.h b/include/clang/Sema/Sema.h
index d5d91e31f5..c9211eb700 100644
--- a/include/clang/Sema/Sema.h
+++ b/include/clang/Sema/Sema.h
@@ -1062,6 +1062,11 @@ public:
 
     llvm::SmallPtrSet<const Expr *, 8> PossibleDerefs;
 
+    /// Expressions appearing as the LHS of a volatile assignment in this
+    /// context. We produce a warning for these when popping the context if
+    /// they are not discarded-value expressions nor unevaluated operands.
+    SmallVector<Expr*, 2> VolatileAssignmentLHSs;
+
     /// \brief Describes whether we are in an expression constext which we have
     /// to handle differently.
     enum ExpressionKind {
@@ -4248,6 +4253,9 @@ public:
   ExprResult TransformToPotentiallyEvaluated(Expr *E);
   ExprResult HandleExprEvaluationContextForTypeof(Expr *E);
 
+  ExprResult CheckUnevaluatedOperand(Expr *E);
+  void CheckUnusedVolatileAssignment(Expr *E);
+
   ExprResult ActOnConstantExpression(ExprResult Res);
 
   // Functions for marking a declaration referenced.  These functions also