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

src/wasm/ast-decoder.cc

Index: src/wasm/ast-decoder.cc
diff --git a/src/wasm/ast-decoder.cc b/src/wasm/ast-decoder.cc
index d596610eb53bc4b89488d60d724449ec49ff99d6..4b6c86c646713d662c0fc2264cd6dd441fce6083 100644
--- a/src/wasm/ast-decoder.cc
+++ b/src/wasm/ast-decoder.cc
@@ -1635,6 +1635,7 @@ class WasmFullDecoder : public WasmDecoder {
                                          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;
@@ -1648,6 +1649,7 @@ class WasmFullDecoder : public WasmDecoder {
     }
 
     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;