[constexpr][c++2a] Try-catch blocks in constexpr functions

Implement support for try-catch blocks in constexpr functions, as
proposed in http://wg21.link/P1002 and voted in San Diego for c++20.

The idea is that we can still never throw inside constexpr, so the catch
block is never entered. A try-catch block like this:

try { f(); } catch (...) { }

is then morally equivalent to just

{ f(); }

Same idea should apply for function/constructor try blocks.

rdar://problem/45530773

Differential Revision: https://reviews.llvm.org/D55097

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@348789 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 40 insertions, 8 deletions

diff --git a/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p3.cpp b/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p3.cpp
index 3986dc9565..ffc408cddb 100644
--- a/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p3.cpp
+++ b/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p3.cpp
@@ -1,5 +1,6 @@
-// RUN: %clang_cc1 -verify -fcxx-exceptions -triple=x86_64-linux-gnu -std=c++11 -Werror=c++1y-extensions %s
-// RUN: %clang_cc1 -verify -fcxx-exceptions -triple=x86_64-linux-gnu -std=c++1y -DCXX1Y %s
+// RUN: %clang_cc1 -verify -fcxx-exceptions -triple=x86_64-linux-gnu -std=c++11 -Werror=c++1y-extensions -Werror=c++2a-extensions %s
+// RUN: %clang_cc1 -verify -fcxx-exceptions -triple=x86_64-linux-gnu -std=c++1y -DCXX1Y -Werror=c++2a-extensions %s
+// RUN: %clang_cc1 -verify -fcxx-exceptions -triple=x86_64-linux-gnu -std=c++2a -DCXX1Y -DCXX2A %s
 
 namespace N {
   typedef char C;
@@ -78,7 +79,12 @@ struct T2 {
 };
 struct T3 {
   constexpr T3 &operator=(const T3&) const = default;
-  // expected-error@-1 {{an explicitly-defaulted copy assignment operator may not have 'const' or 'volatile' qualifiers}}
+#ifndef CXX2A
+  // expected-error@-2 {{an explicitly-defaulted copy assignment operator may not have 'const' or 'volatile' qualifiers}}
+#else
+  // expected-warning@-4 {{explicitly defaulted copy assignment operator is implicitly deleted}}
+  // expected-note@-5 {{function is implicitly deleted because its declared type does not match the type of an implicit copy assignment operator}}
+#endif
 };
 #endif
 struct U {
@@ -129,9 +135,22 @@ constexpr int DisallowedStmtsCXX1Y_2() {
 x:
   return 0;
 }
+constexpr int DisallowedStmtsCXX1Y_2_1() {
+  try {
+    return 0;
+  } catch (...) {
+  merp: goto merp; // expected-error {{statement not allowed in constexpr function}}
+  }
+}
 constexpr int DisallowedStmtsCXX1Y_3() {
   //  - a try-block,
-  try {} catch (...) {} // expected-error {{statement not allowed in constexpr function}}
+  try {} catch (...) {}
+#ifndef CXX2A
+  // expected-error@-2 {{use of this statement in a constexpr function is a C++2a extension}}
+#ifndef CXX1Y
+  // expected-error@-4 {{use of this statement in a constexpr function is a C++14 extension}}
+#endif
+#endif
   return 0;
 }
 constexpr int DisallowedStmtsCXX1Y_4() {
diff --git a/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p4.cpp b/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p4.cpp
index 9c1cab54b6..54aabe6ef3 100644
--- a/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p4.cpp
+++ b/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p4.cpp
@@ -1,5 +1,6 @@
-// RUN: %clang_cc1 -verify -std=c++11 -fcxx-exceptions -Werror=c++1y-extensions %s
-// RUN: %clang_cc1 -verify -std=c++1y -fcxx-exceptions -DCXX1Y %s
+// RUN: %clang_cc1 -verify -std=c++11 -fcxx-exceptions -Werror=c++1y-extensions -Werror=c++2a-extensions %s
+// RUN: %clang_cc1 -verify -std=c++1y -fcxx-exceptions -DCXX1Y -Werror=c++2a-extensions %s
+// RUN: %clang_cc1 -verify -std=c++2a -fcxx-exceptions -DCXX1Y -DCXX2A %s
 
 namespace N {
   typedef char C;
@@ -49,8 +50,14 @@ namespace IndirectVBase {
 // - its function-body shall not be a function-try-block;
 struct U {
   constexpr U()
-    try // expected-error {{function try block not allowed in constexpr constructor}}
+    try
+#ifndef CXX2A
+  // expected-error@-2 {{function try block in constexpr constructor is a C++2a extension}}
+#endif
     : u() {
+#ifndef CXX1Y
+  // expected-error@-2 {{use of this statement in a constexpr constructor is a C++14 extension}}
+#endif
   } catch (...) {
     throw;
   }
diff --git a/test/CXX/drs/dr6xx.cpp b/test/CXX/drs/dr6xx.cpp
index 0f072268ab..f4eccfead2 100644
--- a/test/CXX/drs/dr6xx.cpp
+++ b/test/CXX/drs/dr6xx.cpp
@@ -492,7 +492,13 @@ namespace dr647 { // dr647: yes
   struct C {
     constexpr C(NonLiteral);
     constexpr C(NonLiteral, int) {} // expected-error {{not a literal type}}
-    constexpr C() try {} catch (...) {} // expected-error {{function try block}}
+    constexpr C() try {} catch (...) {}
+#if __cplusplus <= 201703L
+    // expected-error@-2 {{function try block in constexpr constructor is a C++2a extension}}
+#endif
+#if __cplusplus < 201402L
+    // expected-error@-5 {{use of this statement in a constexpr constructor is a C++14 extension}}
+#endif
   };
 
   struct D {