[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 1617 matching lines @@
     if (FLAG_wasm_loop_assignment_analysis) {
       BitVector* assigned = AnalyzeLoopAssignment(pc);
       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);
+        if (failed()) return loop_body_env;

[titzer, 2016/10/13 13:24:42]

I think you should move this up to just after the loop assignment analysis.

[ahaas, 2016/10/13 13:31:55]

Done.

         builder_->StackCheck(position(), &(loop_body_env->effect),
                              &(loop_body_env->control));
         return loop_body_env;
       }
     }
 
     // Conservatively introduce phis for all local variables.
     for (int i = EnvironmentCount() - 1; i >= 0; i--) {
       env->locals[i] =
           builder_->Phi(local_type_vec_[i], 1, &env->locals[i], env->control);
     }
 
     SsaEnv* loop_body_env = Split(env);
+    if (failed()) return loop_body_env;

[titzer, 2016/10/13 13:24:42]

I don't think this check is necessary, since we have one at the beginning of the
function, and the only thing that can make decoding fail until then is the loop
assignment analysis.

[ahaas, 2016/10/13 13:31:55]

Done.

     builder_->StackCheck(position(), &(loop_body_env->effect),
                          &(loop_body_env->control));
     return loop_body_env;
   }
 
   // Create a complete copy of the {from}.
   SsaEnv* Split(SsaEnv* from) {
     DCHECK_NOT_NULL(from);
     SsaEnv* result = reinterpret_cast<SsaEnv*>(zone_->New(sizeof(SsaEnv)));
     size_t size = sizeof(TFNode*) * EnvironmentCount();
@@ skipping 289 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