From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Tue, 8 Apr 2014 12:19:28 +0000 (+0000)
Subject: PR19346: Adding 0 to a null pointer has defined behavior in C++. Allow it in constant... 
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=aee470d9302c5ec5eb3bd21c495c795db1c8de63;p=clang

PR19346: Adding 0 to a null pointer has defined behavior in C++. Allow it in constant expressions.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@205757 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/AST/ExprConstant.cpp b/lib/AST/ExprConstant.cpp
index 9c69080652..16c5a5214d 100644
--- a/lib/AST/ExprConstant.cpp
+++ b/lib/AST/ExprConstant.cpp
@@ -968,7 +968,7 @@ namespace {
       // any object: we won't use such a designator for anything.
       if (!Info.getLangOpts().CPlusPlus11)
         Designator.setInvalid();
-      return checkNullPointer(Info, E, CSK) &&
+      return (CSK == CSK_ArrayToPointer || checkNullPointer(Info, E, CSK)) &&
              Designator.checkSubobject(Info, E, CSK);
     }
 
@@ -986,7 +986,7 @@ namespace {
         Designator.addComplexUnchecked(EltTy, Imag);
     }
     void adjustIndex(EvalInfo &Info, const Expr *E, uint64_t N) {
-      if (checkNullPointer(Info, E, CSK_ArrayIndex))
+      if (N && checkNullPointer(Info, E, CSK_ArrayIndex))
         Designator.adjustIndex(Info, E, N);
     }
   };
diff --git a/test/CXX/expr/expr.const/p2-0x.cpp b/test/CXX/expr/expr.const/p2-0x.cpp
index 84688278f0..bcf45a0c05 100644
--- a/test/CXX/expr/expr.const/p2-0x.cpp
+++ b/test/CXX/expr/expr.const/p2-0x.cpp
@@ -202,7 +202,9 @@ namespace UndefinedBehavior {
     static_assert((A*)nb == 0, "");
     static_assert((B*)na == 0, "");
     constexpr const int &nf = nb->n; // expected-error {{constant expression}} expected-note {{cannot access field of null pointer}}
-    constexpr const int &np = (*(int(*)[4])nullptr)[2]; // expected-error {{constant expression}} expected-note {{cannot access array element of null pointer}}
+    constexpr const int *np1 = (int*)nullptr + 0; // ok
+    constexpr const int *np2 = &(*(int(*)[4])nullptr)[0]; // ok
+    constexpr const int *np3 = &(*(int(*)[4])nullptr)[2]; // expected-error {{constant expression}} expected-note {{cannot perform pointer arithmetic on null pointer}}
 
     struct C {
       constexpr int f() const { return 0; }