[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

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@333703 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 11 insertions, 0 deletions

diff --git a/lib/CodeGen/CGCXXABI.h b/lib/CodeGen/CGCXXABI.h
index a1158d926c..65b50e14f4 100644
--- a/lib/CodeGen/CGCXXABI.h
+++ b/lib/CodeGen/CGCXXABI.h
@@ -607,6 +607,17 @@ CGCXXABI *CreateItaniumCXXABI(CodeGenModule &CGM);
 /// Creates a Microsoft-family ABI.
 CGCXXABI *CreateMicrosoftCXXABI(CodeGenModule &CGM);
 
+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);
+  }
+};
 }
 }