[wasm] Instantiate the interpreter on demand

If a breakpoint is set on a wasm function, compile an interpreter entry
stub for it, and replace all calls to the original function by calls to
this interpreter entry.
Also, instantiate a wasm interpreter object on demand and set the
breakpoint there.

R=titzer@chromium.org
BUG=v8:5822

Review-Url: https://codereview.chromium.org/2625093004
Cr-Commit-Position: refs/heads/master@{#42309}

src/compiler/wasm-compiler.cc

@@ -2949,7 +2949,9 @@ void WasmGraphBuilder::BuildWasmInterpreterEntry(
   }
 
   // The return value is also passed via this buffer:
-  DCHECK_GE(1, sig->return_count());
+  DCHECK_GE(wasm::kV8MaxWasmFunctionReturns, sig->return_count());
+  // TODO(wasm): Handle multi-value returns.
+  DCHECK_EQ(1, wasm::kV8MaxWasmFunctionReturns);
   int return_size_bytes =
       sig->return_count() == 0 ? 0 : 1 << ElementSizeLog2Of(sig->GetReturn(0));
 

src/wasm/wasm-module.cc

@@ -1319,7 +1319,7 @@ class WasmInstanceBuilder {
     //--------------------------------------------------------------------------
     // Set up the exports object for the new instance.
     //--------------------------------------------------------------------------
-    ProcessExports(code_table, instance);
+    ProcessExports(code_table, instance, compiled_module_);
 
     //--------------------------------------------------------------------------
     // Add instance to Memory object
@@ -1781,24 +1781,23 @@ class WasmInstanceBuilder {
     return mem_buffer;
   }
 
-  // Process the exports, creating wrappers for functions, tables, memories,
-  // and globals.
-  void ProcessExports(Handle<FixedArray> code_table,
-                      Handle<WasmInstanceObject> instance) {
-    bool needs_wrappers = module_->num_exported_functions > 0;
+  bool NeedsWrappers() {
+    if (module_->num_exported_functions > 0) return true;
     for (auto table_instance : table_instances_) {
-      if (!table_instance.js_wrappers.is_null()) {
-        needs_wrappers = true;
-        break;
-      }
+      if (!table_instance.js_wrappers.is_null()) return true;
     }
     for (auto table : module_->function_tables) {
-      if (table.exported) {
-        needs_wrappers = true;
-        break;
+      if (table.exported) return true;
     }
+    return false;
   }
-    if (needs_wrappers) {
+
+  // Process the exports, creating wrappers for functions, tables, memories,
+  // and globals.
+  void ProcessExports(Handle<FixedArray> code_table,
+                      Handle<WasmInstanceObject> instance,
+                      Handle<WasmCompiledModule> compiled_module) {
+    if (NeedsWrappers()) {
       // Fill the table to cache the exported JSFunction wrappers.
       js_wrappers_.insert(js_wrappers_.begin(), module_->functions.size(),
                           Handle<JSFunction>::null());
@@ -1826,6 +1825,18 @@ class WasmInstanceBuilder {
         ++export_index;
       }
     }
+
+    // Store weak references to all exported functions.
+    Handle<FixedArray> weak_exported_functions;
+    if (compiled_module->has_weak_exported_functions()) {
+      weak_exported_functions = compiled_module->weak_exported_functions();
+    } else {
+      weak_exported_functions =
+          isolate_->factory()->NewFixedArray(export_index);
+      compiled_module->set_weak_exported_functions(weak_exported_functions);
+    }
+    DCHECK_EQ(export_index, weak_exported_functions->length());
+
     // Process each export in the export table (go in reverse so asm.js
     // can skip duplicates).
     for (auto exp : base::Reversed(module_->export_table)) {
@@ -1858,6 +1869,10 @@ class WasmInstanceBuilder {
             js_wrappers_[exp.index] = js_function;
           }
           desc.set_value(js_function);
+          Handle<WeakCell> weak_export =
+              isolate_->factory()->NewWeakCell(js_function);
+          DCHECK_GT(weak_exported_functions->length(), export_index);
+          weak_exported_functions->set(export_index, *weak_export);
           break;
         }
         case kExternalTable: {

src/wasm/wasm-objects.h

@@ -239,6 +239,7 @@ class WasmCompiledModule : public FixedArray {
   MACRO(WASM_OBJECT, WasmSharedModuleData, shared)    \
   MACRO(OBJECT, Context, native_context)              \
   MACRO(OBJECT, FixedArray, code_table)               \
+  MACRO(OBJECT, FixedArray, weak_exported_functions)  \
   MACRO(OBJECT, FixedArray, function_tables)          \
   MACRO(OBJECT, FixedArray, signature_tables)         \
   MACRO(OBJECT, FixedArray, empty_function_tables)    \
@@ -280,6 +281,7 @@ class WasmCompiledModule : public FixedArray {
     ret->reset_weak_owning_instance();
     ret->reset_weak_next_instance();
     ret->reset_weak_prev_instance();
+    ret->reset_weak_exported_functions();
     return ret;
   }
 
@@ -373,17 +375,22 @@ class WasmCompiledModule : public FixedArray {
   DISALLOW_IMPLICIT_CONSTRUCTORS(WasmCompiledModule);
 };
 
-// TODO(clemensh): Extend this object for breakpoint support, or remove it.
-// TODO(clemensh): Exclude this object from serialization.
 class WasmDebugInfo : public FixedArray {
-  enum Fields { kInstance, kFieldCount };
-
  public:
+  enum Fields {
+    kInstance,
+    kInterpreterHandle,
+    kInterpretedFunctions,
+    kFieldCount
+  };
+
   static Handle<WasmDebugInfo> New(Handle<WasmInstanceObject>);
 
   static bool IsDebugInfo(Object*);
   static WasmDebugInfo* cast(Object*);
 
+  static void SetBreakpoint(Handle<WasmDebugInfo>, int func_index, int offset);
+
   static void RunInterpreter(Handle<WasmDebugInfo>, int func_index,
                              uint8_t* arg_buffer);