[PATCH] D114903: [clang] Support array placement new in constant expressions

[Louis Dionne via Phabricator via cfe-commits]

ldionne created this revision.
ldionne added a reviewer: rsmith.
ldionne requested review of this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

This is necessary for std::construct_at to work on arrays inside a
constant expression.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D114903

Files:
  clang/lib/AST/ExprConstant.cpp
  clang/test/SemaCXX/cxx2a-constexpr-dynalloc.cpp


Index: clang/test/SemaCXX/cxx2a-constexpr-dynalloc.cpp
===================================================================
--- clang/test/SemaCXX/cxx2a-constexpr-dynalloc.cpp
+++ clang/test/SemaCXX/cxx2a-constexpr-dynalloc.cpp
@@ -96,14 +96,28 @@
   return a == 42;
 }
 
+void *operator new[](std::size_t, void *p) { return p; }
+constexpr bool no_array_placement_new_in_user_code() { // expected-error {{never produces a constant expression}}
+  int a[3];
+  new (&a) int[3](); // expected-note {{call to placement 'operator new[]'}}
+  return a[0] == 0 && a[1] == 0 && a[2] == 0;
+}
+
 namespace std {
   constexpr bool placement_new_in_stdlib() {
     int a;
     new (&a) int(42);
     return a == 42;
   }
+
+  constexpr bool array_placement_new_in_stdlib() {
+    int a[3];
+    new (&a) int[3]{42, 43, 44};
+    return a[0] == 42 && a[1] == 43 && a[2] == 44;
+  }
 }
 static_assert(std::placement_new_in_stdlib());
+static_assert(std::array_placement_new_in_stdlib());
 
 namespace std {
   template<typename T, typename ...Args>
Index: clang/lib/AST/ExprConstant.cpp
===================================================================
--- clang/lib/AST/ExprConstant.cpp
+++ clang/lib/AST/ExprConstant.cpp
@@ -9358,8 +9358,7 @@
   bool IsNothrow = false;
   bool IsPlacement = false;
   if (OperatorNew->isReservedGlobalPlacementOperator() &&
-      Info.CurrentCall->isStdFunction() && !E->isArray()) {
-    // FIXME Support array placement new.
+      Info.CurrentCall->isStdFunction()) {
     assert(E->getNumPlacementArgs() == 1);
     if (!EvaluatePointer(E->getPlacementArg(0), Result, Info))
       return false;


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