[WebAssembly] Add -wasm-enable-exnref option (#93597)

This adds `-wasm-enable-exnref`, which will enable the new EH
instructions using `exnref` (adopted in Oct 2023 CG meeting):
https://github.com/WebAssembly/exception-handling/blob/main/proposals/exception-handling/Exceptions.md
This option should be used with `-wasm-enable-eh`.

Author: aheejin

llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCTargetDesc.cpp

@@ -54,6 +54,13 @@ cl::opt<bool>
 // setjmp/longjmp handling using wasm EH instrutions
 cl::opt<bool> WebAssembly::WasmEnableSjLj(
     "wasm-enable-sjlj", cl::desc("WebAssembly setjmp/longjmp handling"));
+// Whether we use the new exnref Wasm EH proposal adopted on Oct 2023.
+// Should be used with -wasm-enable-eh.
+// Currently set to false by default, but will later change to true and then
+// later can be removed after the legacy WAsm EH instructions are removed.
+cl::opt<bool> WebAssembly::WasmEnableExnref(
+    "wasm-enable-exnref", cl::desc("WebAssembly exception handling (exnref)"),
+    cl::init(false));
 
 static MCAsmInfo *createMCAsmInfo(const MCRegisterInfo & /*MRI*/,
                                   const Triple &TT,

llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCTargetDesc.h

@@ -44,6 +44,7 @@ extern cl::opt<bool> WasmEnableEmEH;   // asm.js-style EH
 extern cl::opt<bool> WasmEnableEmSjLj; // asm.js-style SjLJ
 extern cl::opt<bool> WasmEnableEH;     // EH using Wasm EH instructions
 extern cl::opt<bool> WasmEnableSjLj;   // SjLj using Wasm EH instructions
+extern cl::opt<bool> WasmEnableExnref; // EH using new Wasm EH (exnref)
 
 enum OperandType {
   /// Basic block label in a branch construct.

llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp

@@ -385,6 +385,7 @@ FunctionPass *WebAssemblyPassConfig::createTargetRegisterAllocator(bool) {
 using WebAssembly::WasmEnableEH;
 using WebAssembly::WasmEnableEmEH;
 using WebAssembly::WasmEnableEmSjLj;
+using WebAssembly::WasmEnableExnref;
 using WebAssembly::WasmEnableSjLj;
 
 static void basicCheckForEHAndSjLj(TargetMachine *TM) {
@@ -401,6 +402,9 @@ static void basicCheckForEHAndSjLj(TargetMachine *TM) {
   if (WasmEnableEmEH && WasmEnableSjLj)
     report_fatal_error(
         "-enable-emscripten-cxx-exceptions not allowed with -wasm-enable-sjlj");
+  if (WasmEnableExnref && !WasmEnableEH)
+    report_fatal_error(
+        "-wasm-enable-exnref should be used with -wasm-enable-eh");
 
   // Here we make sure TargetOptions.ExceptionModel is the same as
   // MCAsmInfo.ExceptionsType. Normally these have to be the same, because clang

llvm/test/CodeGen/WebAssembly/eh-option-errors.ll

@@ -9,6 +9,9 @@ target triple = "wasm32-unknown-unknown"
 ; RUN: not --crash llc < %s -enable-emscripten-cxx-exceptions -wasm-enable-sjlj 2>&1 | FileCheck %s --check-prefix=EM_EH_W_WASM_SJLJ
 ; EM_EH_W_WASM_SJLJ: LLVM ERROR: -enable-emscripten-cxx-exceptions not allowed with -wasm-enable-sjlj
 
+; RUN: not --crash llc < %s -wasm-enable-exnref 2>&1 | FileCheck %s --check-prefix=WASM_EXNREF_ONLY
+; WASM_EXNREF_ONLY: LLVM ERROR: -wasm-enable-exnref should be used with -wasm-enable-eh
+
 ; RUN: not --crash llc < %s -wasm-enable-eh -exception-model=dwarf 2>&1 | FileCheck %s --check-prefix=EH_MODEL_DWARF
 ; EH_MODEL_DWARF: LLVM ERROR: -exception-model should be either 'none' or 'wasm'