[wasm] Do not generate a loop stack check upon a decoder error.

src/wasm/ast-decoder.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/signature.h"
 
 #include "src/bit-vector.h"
 #include "src/flags.h"
 #include "src/handles.h"
 #include "src/zone/zone-containers.h"
@@ skipping 1609 matching lines @@
   SsaEnv* PrepareForLoop(const byte* pc, SsaEnv* env) {
     if (!builder_) return Split(env);
     if (!env->go()) return Split(env);
     env->state = SsaEnv::kMerged;
 
     env->control = builder_->Loop(env->control);
     env->effect = builder_->EffectPhi(1, &env->effect, env->control);
     builder_->Terminate(env->effect, env->control);
     if (FLAG_wasm_loop_assignment_analysis) {
       BitVector* assigned = AnalyzeLoopAssignment(pc);
+      if (failed()) return env;
       if (assigned != nullptr) {
         // Only introduce phis for variables assigned in this loop.
         for (int i = EnvironmentCount() - 1; i >= 0; i--) {
           if (!assigned->Contains(i)) continue;
           env->locals[i] = builder_->Phi(local_type_vec_[i], 1, &env->locals[i],
                                          env->control);
         }
         SsaEnv* loop_body_env = Split(env);
         builder_->StackCheck(position(), &(loop_body_env->effect),
                              &(loop_body_env->control));
@@ skipping 310 matching lines @@
 BitVector* AnalyzeLoopAssignmentForTesting(Zone* zone, size_t num_locals,
                                            const byte* start, const byte* end) {
   FunctionBody body = {nullptr, nullptr, nullptr, start, end};
   WasmFullDecoder decoder(zone, nullptr, body);
   return decoder.AnalyzeLoopAssignmentForTesting(start, num_locals);
 }
 
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8