From: David Majnemer <david.majnemer@gmail.com>
Date: Fri, 26 Feb 2016 04:23:19 +0000 (+0000)
Subject: [MSVC Compat] Don't evaluate member base expressions w/o side effects
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=e466b31f6a9358b49b2836e319cdc1ad5317d24f;p=clang

[MSVC Compat] Don't evaluate member base expressions w/o side effects

A member expression's base doesn't always have an impact on what the
member decl would evaluate to.  In such a case, the base is used as a
poor man's scope qualifier.

This fixes PR26738.

Differential Revision: http://reviews.llvm.org/D17619

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@261975 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/AST/ExprConstant.cpp b/lib/AST/ExprConstant.cpp
index 4089a20e58..89a21acc84 100644
--- a/lib/AST/ExprConstant.cpp
+++ b/lib/AST/ExprConstant.cpp
@@ -4427,6 +4427,15 @@ public:
   void VisitIgnoredValue(const Expr *E) {
     EvaluateIgnoredValue(Info, E);
   }
+
+  /// Potentially visit a MemberExpr's base expression.
+  void VisitIgnoredBaseExpression(const Expr *E) {
+    // While MSVC doesn't evaluate the base expression, it does diagnose the
+    // presence of side-effecting behavior.
+    if (Info.getLangOpts().MSVCCompat && !E->HasSideEffects(Info.Ctx))
+      return;
+    VisitIgnoredValue(E);
+  }
 };
 
 }
@@ -4750,14 +4759,14 @@ bool LValueExprEvaluator::VisitCXXUuidofExpr(const CXXUuidofExpr *E) {
 bool LValueExprEvaluator::VisitMemberExpr(const MemberExpr *E) {
   // Handle static data members.
   if (const VarDecl *VD = dyn_cast<VarDecl>(E->getMemberDecl())) {
-    VisitIgnoredValue(E->getBase());
+    VisitIgnoredBaseExpression(E->getBase());
     return VisitVarDecl(E, VD);
   }
 
   // Handle static member functions.
   if (const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(E->getMemberDecl())) {
     if (MD->isStatic()) {
-      VisitIgnoredValue(E->getBase());
+      VisitIgnoredBaseExpression(E->getBase());
       return Success(MD);
     }
   }
@@ -6078,7 +6087,7 @@ public:
   }
   bool VisitMemberExpr(const MemberExpr *E) {
     if (CheckReferencedDecl(E, E->getMemberDecl())) {
-      VisitIgnoredValue(E->getBase());
+      VisitIgnoredBaseExpression(E->getBase());
       return true;
     }
 
diff --git a/test/SemaCXX/ms-const-member-expr.cpp b/test/SemaCXX/ms-const-member-expr.cpp
new file mode 100644
index 0000000000..72cfe76fbe
--- /dev/null
+++ b/test/SemaCXX/ms-const-member-expr.cpp
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 %s -std=c++11 -fms-compatibility -fsyntax-only -verify
+
+struct S {
+  enum { E = 1 };
+  static const int sdm = 1;
+};
+
+void f(S *s) {
+  char array[s->E] = { 0 };
+}
+
+extern S *s;
+constexpr int e1 = s->E;
+
+S *side_effect();  // expected-note{{declared here}}
+constexpr int e2 = // expected-error{{must be initialized by a constant expression}}
+    side_effect()->E; // expected-note{{cannot be used in a constant expression}}
+
+constexpr int e4 = s->sdm;