[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

llvm-svn: 348789

1 files changed, 3 insertions, 0 deletions

diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 4150a2454a5..eb690dcfabc 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -4279,6 +4279,9 @@ static EvalStmtResult EvaluateStmt(StmtResult &Result, EvalInfo &Info,
   case Stmt::CaseStmtClass:
   case Stmt::DefaultStmtClass:
     return EvaluateStmt(Result, Info, cast<SwitchCase>(S)->getSubStmt(), Case);
+  case Stmt::CXXTryStmtClass:
+    // Evaluate try blocks by evaluating all sub statements.
+    return EvaluateStmt(Result, Info, cast<CXXTryStmt>(S)->getTryBlock(), Case);
   }
 }