[wasm] Allocate a single script per wasm module

src/objects.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/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <memory>
 #include <sstream>
@@ skipping 13403 matching lines @@
     Handle<FixedArray> array = String::CalculateLineEnds(src, true);
     script->set_line_ends(*array);
   }
 
   DCHECK(script->line_ends()->IsFixedArray());
 }
 
 #define SMI_VALUE(x) (Smi::cast(x)->value())
 bool Script::GetPositionInfo(int position, PositionInfo* info,
                              OffsetFlag offset_flag) {
+  // For wasm, we do not create an artificial line_ends array, but do the
+  // translation directly.
+  if (type() == Script::TYPE_WASM) {

[Yang, 2016/11/15 07:42:25]

InitLineEnds is called from a number of places, which then expect the line_ends
array to hold a FixedArray. Does that work correctly with wasm scripts?

By having the logic for position computation for wasm functions in a separate
place, we duplicate some code (the binary search below, for example). Would it
make sense to somehow unify the line_ends array with wasm's function offset
table?

[Clemens Hammacher, 2016/11/15 15:04:06]

I would like to keep wasm's function offset table "internal" to wasm, and not
expose it to the script. Generating a line_ends array and reusing the existing
logic is problematic, since it makes several assumptions, e.g. that function N
starts one character after the end of function N-1. We would also have to encode
a negative column offset of the script in order to account for the offset of
function 0.
So I think keeping the translation at wasm makes more sense.

With this CL
https://codereview.chromium.org/2451853002
all other usages of InitLineEnds are gone.
I added a DCHECK to InitLineEnds to ensure (and document) that it is never
called for wasm scripts.

+    Handle<wasm::WasmCompiledModule> compiled_module(
+        wasm::WasmCompiledModule::cast(wasm_compiled_module()));
+    DCHECK_LE(0, position);
+    return wasm::GetPositionInfo(compiled_module,
+                                 static_cast<uint32_t>(position), info);
+  }
+
   Handle<Script> script(this);
   InitLineEnds(script);
 
   DisallowHeapAllocation no_allocation;
 
   DCHECK(script->line_ends()->IsFixedArray());
   FixedArray* ends = FixedArray::cast(script->line_ends());
 
   const int ends_len = ends->length();
   if (ends_len == 0) return false;
@@ skipping 6906 matching lines @@
     // Check if the accessor uses a cached property.
     if (!fti->cached_property_name()->IsTheHole(isolate)) {
       return handle(Name::cast(fti->cached_property_name()));
     }
   }
   return MaybeHandle<Name>();
 }
 
 }  // namespace internal
 }  // namespace v8