[WebAssembly] Add throw/rethrow builtins for exception handling

[aheejin]

Summary

Add new builtins for throw/rethrow instructions. This follows exception handling
handling proposal in
https://github.com/WebAssembly/exception-handling/blob/master/proposals/Exceptions.md

[aheejin]

Reverted non-relevant changes

[dschuff]

This looks good. I guess we need to land the intrinsics on the LLVM side first though.

[aheejin]

Uploaded LLVM side patch: https://reviews.llvm.org/D34826

include/clang/Basic/BuiltinsWebAssembly.def

 
 // The format of this database matches clang/Basic/Builtins.def.
 
 // Note that current_memory is not "c" (readnone) because it must be sequenced
 // with respect to grow_memory calls.
 BUILTIN(__builtin_wasm_current_memory, "z", "n")
 BUILTIN(__builtin_wasm_grow_memory, "zz", "n")
 
+// Exception handling builtins.
+BUILTIN(__builtin_wasm_throw, "vUiv*", "r")
+BUILTIN(__builtin_wasm_rethrow, "v", "r")
+
 #undef BUILTIN

lib/CodeGen/CGBuiltin.cpp

case WebAssembly::BI__builtin_wasm_current_memory: {
     Value *Callee = CGM.getIntrinsic(Intrinsic::wasm_current_memory, ResultType);
     return Builder.CreateCall(Callee);
   }
   case WebAssembly::BI__builtin_wasm_grow_memory: {
     Value *X = EmitScalarExpr(E->getArg(0));
     Value *Callee = CGM.getIntrinsic(Intrinsic::wasm_grow_memory, X->getType());
     return Builder.CreateCall(Callee, X);
   }
+  case WebAssembly::BI__builtin_wasm_throw: {
+    Value *Tag = EmitScalarExpr(E->getArg(0));
+    Value *Obj = EmitScalarExpr(E->getArg(1));
+    Value *Callee = CGM.getIntrinsic(Intrinsic::wasm_throw);
+    return Builder.CreateCall(Callee, {Tag, Obj});
+  }
+  case WebAssembly::BI__builtin_wasm_rethrow: {
+    Value *Callee = CGM.getIntrinsic(Intrinsic::wasm_rethrow);
+    return Builder.CreateCall(Callee);
+  }
 
   default:
     return nullptr;
   }
 }

test/CodeGen/builtins-wasm.c

 // RUN: %clang_cc1 -triple wasm32-unknown-unknown -O3 -emit-llvm -o - %s \
 // RUN:   | FileCheck %s -check-prefix=WEBASSEMBLY32
 // RUN: %clang_cc1 -triple wasm64-unknown-unknown -O3 -emit-llvm -o - %s \
 // RUN:   | FileCheck %s -check-prefix=WEBASSEMBLY64
 
 __SIZE_TYPE__ f1(void) {
   return __builtin_wasm_current_memory();
 // WEBASSEMBLY32: call {{i.*}} @llvm.wasm.current.memory.i32()
 // WEBASSEMBLY64: call {{i.*}} @llvm.wasm.current.memory.i64()
 }
 
 __SIZE_TYPE__ f2(__SIZE_TYPE__ delta) {
   return __builtin_wasm_grow_memory(delta);
 // WEBASSEMBLY32: call i32 @llvm.wasm.grow.memory.i32(i32 %{{.*}})
 // WEBASSEMBLY64: call i64 @llvm.wasm.grow.memory.i64(i64 %{{.*}})
 }
+
+void f3(unsigned int tag, void *obj) {
+  return __builtin_wasm_throw(tag, obj);
+// WEBASSEMBLY32: call void @llvm.wasm.throw(i32 %{{.*}}, i8* %{{.*}})
+// WEBASSEMBLY64: call void @llvm.wasm.throw(i32 %{{.*}}, i8* %{{.*}})
+}
+
+void f4() {
+  return __builtin_wasm_rethrow();
+// WEBASSEMBLY32: call void @llvm.wasm.rethrow()
+// WEBASSEMBLY64: call void @llvm.wasm.rethrow()
+}