[PATCH] D158601: [Clang] Always constant-evaluate operands of comparisons to nullptr

[Corentin Jabot via Phabricator via cfe-commits]

cor3ntin updated this revision to Diff 553038.
cor3ntin added a comment.

Rebase


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D158601/new/

https://reviews.llvm.org/D158601

Files:
  clang/docs/ReleaseNotes.rst
  clang/lib/AST/ExprConstant.cpp
  clang/test/SemaCXX/compare-cxx2a.cpp


Index: clang/test/SemaCXX/compare-cxx2a.cpp
===================================================================
--- clang/test/SemaCXX/compare-cxx2a.cpp
+++ clang/test/SemaCXX/compare-cxx2a.cpp
@@ -461,3 +461,21 @@
   template<typename T> bool f6() { return 0 < y6; } // expected-note {{instantiation of}}
   void g6() { f6<int>(); } // expected-note {{instantiation of}}
 }
+
+
+namespace GH64923 {
+using nullptr_t = decltype(nullptr);
+struct MyTask{};
+constexpr MyTask DoAnotherThing() {
+    return {};
+}
+
+constexpr nullptr_t operator++(MyTask &&T); // expected-note 2{{declared here}}
+void DoSomething() {
+  if constexpr (++DoAnotherThing() != nullptr) {} // expected-error {{constexpr if condition is not a constant expression}} \
+                                                  // expected-note  {{undefined function 'operator++' cannot be used in a constant expression}}
+
+  if constexpr (nullptr == ++DoAnotherThing()) {} // expected-error {{constexpr if condition is not a constant expression}} \
+                                                  // expected-note  {{undefined function 'operator++' cannot be used in a constant expression}}
+}
+}
Index: clang/lib/AST/ExprConstant.cpp
===================================================================
--- clang/lib/AST/ExprConstant.cpp
+++ clang/lib/AST/ExprConstant.cpp
@@ -13310,6 +13310,10 @@
     // C++11 [expr.rel]p4, [expr.eq]p3: If two operands of type std::nullptr_t
     // are compared, the result is true of the operator is <=, >= or ==, and
     // false otherwise.
+    LValue Res;
+    if (!EvaluatePointer(E->getLHS(), Res, Info) ||
+        !EvaluatePointer(E->getRHS(), Res, Info))
+      return false;
     return Success(CmpResult::Equal, E);
   }
 
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -198,6 +198,11 @@
 - Update ``FunctionDeclBitfields.NumFunctionDeclBits``. This fixes:
   (`#64171 <https://github.com/llvm/llvm-project/issues/64171>`_).
 
+- Expressions producing ``nullptr`` are correctly evaluated
+  by the constant interpreter when appearing as the operand
+  of a binary comparision.
+  (`#64923 <https://github.com/llvm/llvm-project/issues/64923>_``)
+
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 - Fixed an import failure of recursive friend class template.


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