[wasm] Add testing opcode to test unsupported opcodes in Liftoff

Liftoff is not fully feature complete yet. To test that Liftoff can
bailout to TurboFan also for debugging, this CL adds
* an opcode that is only implemented in TurboFan
* a flag that allows that opcode to be compiled with TurboFan
* a bailout for this opcode to Liftoff.

R=clemensb@chromium.org

Bug: v8:7581
Change-Id: Ie4b4654d0d36ab937a7dfe9b1bb6a187b17615fb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2629284
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72113}

src/flags/flag-definitions.h

@@ -824,6 +824,9 @@ DEFINE_NEG_IMPLICATION(liftoff_only, wasm_tier_up)
 DEFINE_NEG_IMPLICATION(fuzzing, liftoff_only)
 DEFINE_BOOL(experimental_liftoff_extern_ref, false,
             "enable support for externref in Liftoff")
+DEFINE_DEBUG_BOOL(
+    enable_testing_opcode_in_wasm, false,
+    "enables a testing opcode in wasm that is only implemented in TurboFan")
 // We can't tier up (from Liftoff to TurboFan) in single-threaded mode, hence
 // disable tier up in that configuration for now.
 DEFINE_NEG_IMPLICATION(single_threaded, wasm_tier_up)

src/wasm/baseline/liftoff-compiler.cc

@@ -1997,6 +1997,10 @@ class LiftoffCompiler {
     __ AssertUnreachable(AbortReason::kUnexpectedReturnFromWasmTrap);
   }
 
+  void NopForTestingUnsupportedInLiftoff(FullDecoder* decoder) {
+    unsupported(decoder, kOtherReason, "testing opcode");
+  }
+
   void Select(FullDecoder* decoder, const Value& cond, const Value& fval,
               const Value& tval, Value* result) {
     LiftoffRegList pinned;

src/wasm/function-body-decoder-impl.h

@@ -1008,6 +1008,7 @@ struct ControlBase : public PcForErrors<validate> {
   F(TableSet, const Value& index, const Value& value,                          \
     const TableIndexImmediate<validate>& imm)                                  \
   F(Unreachable)                                                               \
+  F(NopForTestingUnsupportedInLiftoff)                                         \
   F(Select, const Value& cond, const Value& fval, const Value& tval,           \
     Value* result)                                                             \
   F(BrOrRet, uint32_t depth)                                                   \
@@ -1620,6 +1621,7 @@ class WasmDecoder : public Decoder {
       /********** Control opcodes **********/
       case kExprUnreachable:
       case kExprNop:
+      case kExprNopForTestingUnsupportedInLiftoff:
       case kExprElse:
       case kExprEnd:
       case kExprReturn:
@@ -2016,6 +2018,7 @@ class WasmDecoder : public Decoder {
       case kExprTry:
       case kExprCatch:
       case kExprNop:
+      case kExprNopForTestingUnsupportedInLiftoff:
       case kExprReturn:
       case kExprReturnCall:
       case kExprReturnCallIndirect:
@@ -2384,6 +2387,15 @@ class WasmFullDecoder : public WasmDecoder<validate> {
 
   DECODE(Nop) { return 1; }
 
+  DECODE(NopForTestingUnsupportedInLiftoff) {
+    if (!VALIDATE(FLAG_enable_testing_opcode_in_wasm)) {
+      this->DecodeError("Invalid opcode 0x%x", opcode);
+      return 0;
+    }
+    CALL_INTERFACE_IF_REACHABLE(NopForTestingUnsupportedInLiftoff);
+    return 1;
+  }
+
 #define BUILD_SIMPLE_OPCODE(op, _, sig) \
   DECODE(op) { return BuildSimpleOperator_##sig(kExpr##op); }
   FOREACH_SIMPLE_OPCODE(BUILD_SIMPLE_OPCODE)
@@ -3237,6 +3249,7 @@ class WasmFullDecoder : public WasmDecoder<validate> {
     DECODE_IMPL(BrTable);
     DECODE_IMPL(Return);
     DECODE_IMPL(Unreachable);
+    DECODE_IMPL(NopForTestingUnsupportedInLiftoff);
     DECODE_IMPL(I32Const);
     DECODE_IMPL(I64Const);
     DECODE_IMPL(F32Const);

src/wasm/graph-builder-interface.cc

@@ -439,6 +439,8 @@ class WasmGraphBuildingInterface {
     BUILD(Trap, wasm::TrapReason::kTrapUnreachable, decoder->position());
   }
 
+  void NopForTestingUnsupportedInLiftoff(FullDecoder* decoder) {}
+
   void Select(FullDecoder* decoder, const Value& cond, const Value& fval,
               const Value& tval, Value* result) {
     TFNode* controls[2];

src/wasm/wasm-opcodes-inl.h

@@ -138,6 +138,7 @@ constexpr const char* WasmOpcodes::OpcodeName(WasmOpcode opcode) {
     CASE_I64_OP(SExtendI32, "extend32_s")
     CASE_OP(Unreachable, "unreachable")
     CASE_OP(Nop, "nop")
+    CASE_OP(NopForTestingUnsupportedInLiftoff, "nop_for_testing")
     CASE_OP(Block, "block")
     CASE_OP(Loop, "loop")
     CASE_OP(If, "if")

src/wasm/wasm-opcodes.h

@@ -46,7 +46,8 @@ bool V8_EXPORT_PRIVATE IsJSCompatibleSignature(const FunctionSig* sig,
   V(Return, 0x0f, _)                            \
   V(Delegate, 0x16, _ /* eh_prototype */)       \
   V(Let, 0x17, _ /* typed_funcref prototype */) \
-  V(BrOnNull, 0xd4, _ /* gc prototype */)
+  V(BrOnNull, 0xd4, _ /* gc prototype */)       \
+  V(NopForTestingUnsupportedInLiftoff, 0x18, _)
 
 // Constants, locals, globals, and calls.
 #define FOREACH_MISC_OPCODE(V)                            \

test/debugger/debug/wasm/debug-enabled-tier-down-wasm-unsupported-liftoff.js

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --experimental-wasm-reftypes
+// Flags: --enable-testing-opcode-in-wasm
 
 // Test that tiering up and tiering down works even if functions cannot be
 // compiled with Liftoff.
@@ -11,11 +11,12 @@ load('test/mjsunit/wasm/wasm-module-builder.js');
 
 // Create a simple Wasm module.
 function create_builder(i) {
+  const kExprNopForTestingUnsupportedInLiftoff = 0x18;
   const builder = new WasmModuleBuilder();
-  builder.addFunction('main', kSig_i_r)
+  builder.addFunction('main', kSig_i_i)
       .addBody([
-        kExprLocalGet, 0, kExprRefIsNull, ...wasmI32Const(i),
-        kExprI32Add
+        kExprLocalGet, 0, kExprNopForTestingUnsupportedInLiftoff,
+        ...wasmI32Const(i), kExprI32Add
       ])
       .exportFunc();
   return builder;

test/debugger/debugger.status

@@ -117,6 +117,10 @@
   'debug/debug-stepout-scope-part8': [SKIP],
 }],  # 'arch == arm and mode == debug'
 
+['mode != debug', {
+  # Test uses a flag only available in debug mode
+  'debug/wasm/debug-enabled-tier-down-wasm-unsupported-liftoff': [SKIP],
+}],
 ##############################################################################
 ['arch == s390 or arch == s390x', {