Address review comments

Author: tbaederr

clang/include/clang/Basic/DiagnosticASTKinds.td

@@ -90,16 +90,18 @@ def note_constexpr_pointer_subtraction_not_same_array : Note<
 def note_constexpr_pointer_subtraction_zero_size : Note<
   "subtraction of pointers to type %0 of zero size">;
 def note_constexpr_pointer_comparison_unspecified : Note<
-  "comparison between '%0' and '%1' has unspecified value">;
+  "comparison between pointers to unrelated objects '%0' and '%1' has unspecified value">;
 def note_constexpr_pointer_arith_unspecified : Note<
-  "arithmetic involving '%0' and '%1' has unspecified value">;
+  "arithmetic involving unrelated objects '%0' and '%1' has unspecified value">;
 def note_constexpr_pointer_constant_comparison : Note<
   "comparison of numeric address '%0' with pointer '%1' can only be performed "
   "at runtime">;
 def note_constexpr_literal_comparison : Note<
-  "comparison of addresses of literals has unspecified value">;
+  "comparison of addresses of potentially overlapping literals has unspecified value">;
 def note_constexpr_literal_arith : Note<
-  "arithmetic on addresses of literals has unspecified value">;
+  "arithmetic on addresses of potentially overlapping literals has unspecified value">;
+def note_constexpr_repeated_literal_eval : Note<
+  "repeated evaluation of the same literal expression can produce different objects">;
 def note_constexpr_opaque_call_comparison : Note<
   "comparison against opaque constant address '%0' can only be performed at "
   "runtime">;

clang/lib/AST/ExprConstant.cpp

@@ -14588,20 +14588,23 @@ bool IntExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) {
         return Error(E);
       const Expr *LHSExpr = LHSValue.Base.dyn_cast<const Expr *>();
       const Expr *RHSExpr = RHSValue.Base.dyn_cast<const Expr *>();
-      if (!LHSExpr || !RHSExpr) {
-        std::string LHS = LHSValue.toString(Info.Ctx, E->getLHS()->getType());
-        std::string RHS = RHSValue.toString(Info.Ctx, E->getRHS()->getType());
-        Info.FFDiag(E, diag::note_constexpr_pointer_arith_unspecified)
-            << LHS << RHS;
-        return false;
-      }
 
-      if (ArePotentiallyOverlappingStringLiterals(Info, LHSValue, RHSValue)) {
-        std::string LHS = LHSValue.toString(Info.Ctx, E->getLHS()->getType());
-        std::string RHS = RHSValue.toString(Info.Ctx, E->getRHS()->getType());
-        Info.FFDiag(E, diag::note_constexpr_literal_arith) << LHS << RHS;
+      auto DiagArith = [&](unsigned DiagID) {
+        std::string LHS = LHSValue.toString(Info.Ctx, LHSExpr->getType());
+        std::string RHS = RHSValue.toString(Info.Ctx, RHSExpr->getType());
+        Info.FFDiag(E, DiagID) << LHS << RHS;
+        if (LHSExpr && LHSExpr == RHSExpr)
+          Info.Note(LHSExpr->getExprLoc(),
+                    diag::note_constexpr_repeated_literal_eval)
+              << LHSExpr->getSourceRange();
         return false;
-      }
+      };
+
+      if (!LHSExpr || !RHSExpr)
+        return DiagArith(diag::note_constexpr_pointer_arith_unspecified);
+
+      if (ArePotentiallyOverlappingStringLiterals(Info, LHSValue, RHSValue))
+        return DiagArith(diag::note_constexpr_literal_arith);
 
       const AddrLabelExpr *LHSAddrExpr = dyn_cast<AddrLabelExpr>(LHSExpr);
       const AddrLabelExpr *RHSAddrExpr = dyn_cast<AddrLabelExpr>(RHSExpr);