[WebAssembly] Change wasm.throw's first argument to an immediate

[aheejin]

Summary

wasm.throw builtin's first 'tag' argument should be an immediate index
into the event section.

[dschuff]

LGTM; I wonder if it makes sense to have predefined macro for the C++ tag (or perhaps just a regular macro for use in libcxxabi?)

[craig.topper]

Shouldn't the definition in BuiltinsWebAssembly.def be updated to include an 'I' in the type string so that this will be properly diagnosed in the frontend?

[aheejin]

In D59448#1433607, @dschuff wrote:

LGTM; I wonder if it makes sense to have predefined macro for the C++ tag (or perhaps just a regular macro for use in libcxxabi?)

The only place the throw builtin will be used in within __cxa_throw function in libcxxabi, so I guess some regular macro in libcxxabi would be fine.

[aheejin]

• Add I to wasm.throw builtin's tag argument

[aheejin]

In D59448#1433622, @craig.topper wrote:

Shouldn't the definition in BuiltinsWebAssembly.def be updated to include an 'I' in the type string so that this will be properly diagnosed in the frontend?

Done. Thank you for checking!

test/CodeGen/builtins-wasm.c

 }
 
 void data_drop() {
   __builtin_wasm_data_drop(3);
   // WEBASSEMBLY32: call void @llvm.wasm.data.drop(i32 3)
   // WEBASSEMBLY64: call void @llvm.wasm.data.drop(i32 3)
 }
 
-void throw(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 throw(void *obj) {
+  return __builtin_wasm_throw(0, obj);
+  // WEBASSEMBLY32: call void @llvm.wasm.throw(i32 0, i8* %{{.*}})
+  // WEBASSEMBLY64: call void @llvm.wasm.throw(i32 0, i8* %{{.*}})
 }
 
 void rethrow_in_catch(void) {
   return __builtin_wasm_rethrow_in_catch();
   // WEBASSEMBLY32: call void @llvm.wasm.rethrow.in.catch()
   // WEBASSEMBLY64: call void @llvm.wasm.rethrow.in.catch()
 }