Revert of [wasm] Enforce that function bodies end with the \"end\" opcode.

src/wasm/function-body-decoder.cc

Index: src/wasm/function-body-decoder.cc
diff --git a/src/wasm/function-body-decoder.cc b/src/wasm/function-body-decoder.cc
index 152fba1ffe92a42b9cd27c05f1180134cde89ef9..b50d97eb3d01602dfa4d73ab31da186f755db5b1 100644
--- a/src/wasm/function-body-decoder.cc
+++ b/src/wasm/function-body-decoder.cc
@@ -39,6 +39,8 @@
     error("Invalid opcode (enable with --" #flag ")");         \
     break;                                                     \
   }
+// TODO(titzer): this is only for intermediate migration.
+#define IMPLICIT_FUNCTION_END 1
 
 // An SsaEnv environment carries the current local variable renaming
 // as well as the current effect and control dependency in the TF graph.
@@ -491,14 +493,41 @@
 
     if (failed()) return TraceFailed();
 
+#if IMPLICIT_FUNCTION_END
+    // With implicit end support (old style), the function block
+    // remains on the stack. Other control blocks are an error.
+    if (control_.size() > 1) {
+      error(pc_, control_.back().pc, "unterminated control structure");
+      return TraceFailed();
+    }
+
+    // Assume an implicit end to the function body block.
+    if (control_.size() == 1) {
+      Control* c = &control_.back();
+      if (ssa_env_->go()) {
+        FallThruTo(c);
+      }
+
+      if (c->end_env->go()) {
+        // Push the end values onto the stack.
+        stack_.resize(c->stack_depth);
+        if (c->merge.arity == 1) {
+          stack_.push_back(c->merge.vals.first);
+        } else {
+          for (unsigned i = 0; i < c->merge.arity; i++) {
+            stack_.push_back(c->merge.vals.array[i]);
+          }
+        }
+
+        TRACE("  @%-8d #xx:%-20s|", startrel(pc_), "ImplicitReturn");
+        SetEnv("function:end", c->end_env);
+        DoReturn();
+        TRACE("\n");
+      }
+    }
+#else
     if (!control_.empty()) {
-      // Generate a better error message whether the unterminated control
-      // structure is the function body block or an innner structure.
-      if (control_.size() > 1) {
-        error(pc_, control_.back().pc, "unterminated control structure");
-      } else {
-        error("function body must end with \"end\" opcode.");
-      }
+      error(pc_, control_.back().pc, "unterminated control structure");
       return TraceFailed();
     }
 
@@ -506,6 +535,7 @@
       error("function body must end with \"end\" opcode.");
       return false;
     }
+#endif
 
     if (FLAG_trace_wasm_decode_time) {
       double ms = decode_timer.Elapsed().InMillisecondsF();