[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, 0 insertions, 14 deletions

diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index a8260b49ed9..a58982bd0c9 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -859,20 +859,6 @@ void MicrosoftCXXABI::emitRethrow(CodeGenFunction &CGF, bool isNoReturn) {
     CGF.EmitRuntimeCallOrInvoke(Fn, Args);
 }
 
-namespace {
-struct CatchRetScope final : EHScopeStack::Cleanup {
-  llvm::CatchPadInst *CPI;
-
-  CatchRetScope(llvm::CatchPadInst *CPI) : CPI(CPI) {}
-
-  void Emit(CodeGenFunction &CGF, Flags flags) override {
-    llvm::BasicBlock *BB = CGF.createBasicBlock("catchret.dest");
-    CGF.Builder.CreateCatchRet(CPI, BB);
-    CGF.EmitBlock(BB);
-  }
-};
-}
-
 void MicrosoftCXXABI::emitBeginCatch(CodeGenFunction &CGF,
                                      const CXXCatchStmt *S) {
   // In the MS ABI, the runtime handles the copy, and the catch handler is