[WebAssembly] Use Windows EH instructions for Wasm EH

Summary:
Because wasm control flow needs to be structured, using WinEH
instructions to support wasm EH brings several benefits. This patch
makes wasm EH uses Windows EH instructions, with some changes:
1. Because wasm uses a single catch block to catch all C++ exceptions,
   this merges all catch clauses into a single catchpad, within which we
   test the EH selector as in Itanium EH.
2. Generates a call to `__clang_call_terminate` in case a cleanup
   throws. Wasm does not have a runtime to handle this.
3. In case there is no catch-all clause, inserts a call to
   `__cxa_rethrow` at the end of a catchpad in order to unwind to an
   enclosing EH scope.

Reviewers: majnemer, dschuff

Subscribers: jfb, sbc100, jgravelle-google, sunfish, cfe-commits

Differential Revision: https://reviews.llvm.org/D44931

llvm-svn: 333703

1 files changed, 6 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CGCleanup.h b/clang/lib/CodeGen/CGCleanup.h
index 105c5629d50..5530350b9b7 100644
--- a/clang/lib/CodeGen/CGCleanup.h
+++ b/clang/lib/CodeGen/CGCleanup.h
@@ -627,16 +627,21 @@ struct EHPersonality {
   static const EHPersonality MSVC_except_handler;
   static const EHPersonality MSVC_C_specific_handler;
   static const EHPersonality MSVC_CxxFrameHandler3;
+  static const EHPersonality GNU_Wasm_CPlusPlus;
 
   /// Does this personality use landingpads or the family of pad instructions
   /// designed to form funclets?
-  bool usesFuncletPads() const { return isMSVCPersonality(); }
+  bool usesFuncletPads() const {
+    return isMSVCPersonality() || isWasmPersonality();
+  }
 
   bool isMSVCPersonality() const {
     return this == &MSVC_except_handler || this == &MSVC_C_specific_handler ||
            this == &MSVC_CxxFrameHandler3;
   }
 
+  bool isWasmPersonality() const { return this == &GNU_Wasm_CPlusPlus; }
+
   bool isMSVCXXPersonality() const { return this == &MSVC_CxxFrameHandler3; }
 };
 }