P0217R3: Constant expression evaluation for decomposition declarations.

llvm-svn: 278447

4 files changed, 60 insertions, 6 deletions

diff --git a/clang/test/CXX/dcl.decl/dcl.decomp/p2.cpp b/clang/test/CXX/dcl.decl/dcl.decomp/p2.cpp
index cd0518bfc59..639aff64dfc 100644
--- a/clang/test/CXX/dcl.decl/dcl.decomp/p2.cpp
+++ b/clang/test/CXX/dcl.decl/dcl.decomp/p2.cpp
@@ -1,7 +1,7 @@
 // RUN: %clang_cc1 -std=c++1z -verify %s
 
 int array() {
-  int arr[3] = {};
+  static int arr[3] = {};
   // FIXME: We are supposed to create an array object here and perform elementwise initialization.
   auto [a, b, c] = arr; // expected-error {{cannot decompose non-class, non-array}}
 
@@ -11,8 +11,9 @@ int array() {
   auto &[r0, r1, r2] = arr;
   const auto &[cr0, cr1, cr2] = arr;
 
-  //static_assert(&arr[0] == &r0);
-  //static_assert(&arr[0] == &cr0);
+  static_assert(&arr[0] == &r0);
+  static_assert(&arr[0] == &cr0);
+
   using T = int;
   using T = decltype(r0);
   using U = const int;
diff --git a/clang/test/CXX/dcl.decl/dcl.decomp/p3.cpp b/clang/test/CXX/dcl.decl/dcl.decomp/p3.cpp
index 1acf391c9f3..e4a7a6c4f98 100644
--- a/clang/test/CXX/dcl.decl/dcl.decomp/p3.cpp
+++ b/clang/test/CXX/dcl.decl/dcl.decomp/p3.cpp
@@ -201,3 +201,32 @@ void test_value_category() {
   { auto [a] = wrap<const int, void, float&>(); } // ok, const int &a can bind to float
   { auto [a] = wrap<int, void, float>(); } // ok, int &&a can bind to float
 }
+
+namespace constant {
+  struct Q {};
+  template<int N> constexpr int get(Q &&) { return N * N; }
+}
+template<> struct std::tuple_size<constant::Q> { static const int value = 3; };
+template<int N> struct std::tuple_element<N, constant::Q> { typedef int type; };
+namespace constant {
+  Q q;
+  // This creates and lifetime-extends a temporary to hold the result of each get() call.
+  auto [a, b, c] = q;    // expected-note {{temporary}}
+  static_assert(a == 0); // expected-error {{constant expression}} expected-note {{temporary}}
+
+  constexpr bool f() {
+    auto [a, b, c] = q;
+    return a == 0 && b == 1 && c == 4;
+  }
+  static_assert(f());
+
+  constexpr int g() {
+    int *p = nullptr;
+    {
+      auto [a, b, c] = q;
+      p = &c;
+    }
+    return *p; // expected-note {{read of object outside its lifetime}}
+  }
+  static_assert(g() == 4); // expected-error {{constant}} expected-note {{in call to 'g()'}}
+}
diff --git a/clang/test/CXX/dcl.decl/dcl.decomp/p4.cpp b/clang/test/CXX/dcl.decl/dcl.decomp/p4.cpp
index 3a72ae0e33a..ea225cbf9ab 100644
--- a/clang/test/CXX/dcl.decl/dcl.decomp/p4.cpp
+++ b/clang/test/CXX/dcl.decl/dcl.decomp/p4.cpp
@@ -163,6 +163,14 @@ namespace Bitfield {
   }
 }
 
+namespace Constexpr {
+  struct Q { int a, b; constexpr Q() : a(1), b(2) {} };
+  constexpr Q q;
+  auto &[qa, qb] = q;
+  static_assert(&qa == &q.a && &qb == &q.b);
+  static_assert(qa == 1 && qb == 2);
+}
+
 namespace std_example {
   struct S { int x1 : 2; volatile double y1; };
   S f();
diff --git a/clang/test/SemaCXX/cxx1z-decomposition.cpp b/clang/test/SemaCXX/cxx1z-decomposition.cpp
index 6541476a67b..3b1e49cb078 100644
--- a/clang/test/SemaCXX/cxx1z-decomposition.cpp
+++ b/clang/test/SemaCXX/cxx1z-decomposition.cpp
@@ -6,9 +6,13 @@ void use_from_own_init() {
 
 // As a Clang extension, _Complex can be decomposed.
 float decompose_complex(_Complex float cf) {
+  static _Complex float scf;
+  auto &[sre, sim] = scf;
+  // ok, this is references initialized by constant expressions all the way down
+  static_assert(&sre == &__real scf);
+  static_assert(&sim == &__imag scf);
+
   auto [re, im] = cf;
-  //static_assert(&re == &__real cf);
-  //static_assert(&im == &__imag cf);
   return re*re + im*im;
 }
 
@@ -20,8 +24,20 @@ float decompose_vector(vf3 v) {
   return x + y + z;
 }
 
+struct S { int a, b; };
+constexpr int f(S s) {
+  auto &[a, b] = s;
+  return a * 10 + b;
+}
+static_assert(f({1, 2}) == 12);
+
+constexpr bool g(S &&s) { 
+  auto &[a, b] = s;
+  return &a == &s.a && &b == &s.b && &a != &b;
+}
+static_assert(g({1, 2}));
+
 // FIXME: by-value array copies
 // FIXME: template instantiation
 // FIXME: ast file support
 // FIXME: code generation
-// FIXME: constant expression evaluation