[asm.js] [wasm] Store function start position for stack check

src/wasm/function-body-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 533 matching lines @@
                local_type_vec_[index] == type) {
           // Do a whole run of like-typed locals at a time.
           ssa_env->locals[index++] = node;
         }
       }
     }
     ssa_env->control = start;
     ssa_env->effect = start;
     SetEnv("initial", ssa_env);
     if (builder_) {
-      builder_->StackCheck(position());
+      // The function-prologue stack check is associated with position 0, which
+      // is never a position of any instruction in the function.
+      builder_->StackCheck(0);
     }
   }
 
   TFNode* DefaultValue(ValueType type) {
     switch (type) {
       case kWasmI32:
         return builder_->Int32Constant(0);
       case kWasmI64:
         return builder_->Int64Constant(0);
       case kWasmF32:
@@ skipping 1506 matching lines @@
 BitVector* AnalyzeLoopAssignmentForTesting(Zone* zone, size_t num_locals,
                                            const byte* start, const byte* end) {
   FunctionBody body = {nullptr, nullptr, start, end};
   WasmFullDecoder decoder(zone, body);
   return decoder.AnalyzeLoopAssignmentForTesting(start, num_locals);
 }
 
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8