[wasm] Allocate a single script per wasm module

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 89c40c1022b9046b3e31692270cdb01d414cd7fd..c11facb603f6014a2aaa2c2284ea71fe51e160d7 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -13421,6 +13421,16 @@ void Script::InitLineEnds(Handle<Script> script) {
 #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);