[clang] [clang][ExprConst] Reject field access with nullptr base (PR #113885)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/113885

Reject them if the base is null, not only if the entire pointer is null.

>From 66d42412ddd22e0e4da293990d16a4d7692f973c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Mon, 28 Oct 2024 10:04:46 +0100
Subject: [PATCH] [clang][ExprConst] Reject field access with nullptr base

---
 clang/lib/AST/ExprConstant.cpp           | 2 +-
 clang/test/CXX/expr/expr.const/p2-0x.cpp | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 8e36cad2d2c6e7..a6694bc0641508 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -1703,7 +1703,7 @@ namespace {
     bool checkNullPointerDiagnosingWith(const GenDiagType &GenDiag) {
       if (Designator.Invalid)
         return false;
-      if (IsNullPtr) {
+      if (getLValueBase().isNull()) {
         GenDiag();
         Designator.setInvalid();
         return false;
diff --git a/clang/test/CXX/expr/expr.const/p2-0x.cpp b/clang/test/CXX/expr/expr.const/p2-0x.cpp
index 767eee1c74f054..67160ba571f33c 100644
--- a/clang/test/CXX/expr/expr.const/p2-0x.cpp
+++ b/clang/test/CXX/expr/expr.const/p2-0x.cpp
@@ -188,7 +188,7 @@ namespace UndefinedBehavior {
 
   namespace Ptr {
     struct A {};
-    struct B : A { int n; };
+    struct B : A { int n; int m; };
     B a[3][3];
     constexpr B *p = a[0] + 4; // expected-error {{constant expression}} expected-note {{element 4 of array of 3 elements}}
     B b = {};
@@ -204,6 +204,7 @@ 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 &mf = nb->m; // expected-error {{constant expression}} expected-note {{cannot access field 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}}