[wasm] Add stack checks to loops.

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 025ccdf1d7bfc0d2c159e511600b0d313cf0fa9b..86a5e652af04060f08339d8ad4a58953f9aba331 100644
--- a/src/wasm/ast-decoder.cc
+++ b/src/wasm/ast-decoder.cc
@@ -684,8 +684,7 @@ class WasmFullDecoder : public WasmDecoder {
             BlockTypeOperand operand(this, pc_);
             SsaEnv* finish_try_env = Steal(ssa_env_);
             // The continue environment is the inner environment.
-            PrepareForLoop(pc_, finish_try_env);
-            SetEnv("loop:start", Split(finish_try_env));
+            SetEnv("loop:start", PrepareForLoop(pc_, finish_try_env));

[titzer, 2016/10/12 19:16:25]

Please introduce a local variable here to make it clear that the environment
returned by PrepareForLoop is the body environment.

[ahaas, 2016/10/13 10:51:55]

Done.

             ssa_env_->SetNotMerged();
             PushLoop(finish_try_env);
             SetBlockType(&control_.back(), operand);
@@ -1611,10 +1610,15 @@ class WasmFullDecoder : public WasmDecoder {
     return tnode;
   }
 
-  void PrepareForLoop(const byte* pc, SsaEnv* env) {
-    if (!env->go()) return;
+  SsaEnv* BuildLoopStackCheck(SsaEnv* env) {

[titzer, 2016/10/12 19:16:25]

You can inline this.

[ahaas, 2016/10/13 10:51:55]

Done.

+    builder_->StackCheck(position(), &(env->effect), &(env->control));
+    return env;
+  }
+
+  SsaEnv* PrepareForLoop(const byte* pc, SsaEnv* env) {
+    if (!builder_) return Split(env);
+    if (!env->go()) return BuildLoopStackCheck(Split(env));

[titzer, 2016/10/12 19:16:25]

You shouldn't build the stack check if the ssa environment isn't reachable.

[ahaas, 2016/10/13 10:51:55]

Done.

     env->state = SsaEnv::kMerged;
-    if (!builder_) return;
 
     env->control = builder_->Loop(env->control);
     env->effect = builder_->EffectPhi(1, &env->effect, env->control);
@@ -1628,7 +1632,7 @@ class WasmFullDecoder : public WasmDecoder {
           env->locals[i] = builder_->Phi(local_type_vec_[i], 1, &env->locals[i],
                                          env->control);
         }
-        return;
+        return BuildLoopStackCheck(Split(env));
       }
     }
 
@@ -1637,6 +1641,8 @@ class WasmFullDecoder : public WasmDecoder {
       env->locals[i] =
           builder_->Phi(local_type_vec_[i], 1, &env->locals[i], env->control);
     }
+
+    return BuildLoopStackCheck(Split(env));
   }
 
   // Create a complete copy of the {from}.