[wasm] Add --trace-wasm-ast-start and --trace-wasm-ast-end options and improve tracing.

src/compiler/wasm-compiler.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/compiler/wasm-compiler.h"
 
 #include "src/isolate-inl.h"
 
 #include "src/base/platform/elapsed-timer.h"
 #include "src/base/platform/platform.h"
@@ skipping 2576 matching lines @@
     // Add the function as another context for the exception
     ScopedVector<char> buffer(128);
     wasm::WasmName name =
         module_env->module->GetName(function.name_offset, function.name_length);
     SNPrintF(buffer, "Compiling WASM function #%d:%.*s failed:",
              function.func_index, name.length, name.name);
     thrower.Failed(buffer.start(), result);
     return Handle<Code>::null();
   }
 
+  int index = static_cast<int>(function.func_index);
+  if (index >= FLAG_trace_wasm_ast_start && index < FLAG_trace_wasm_ast_end) {
+    PrintAst(body);
+  }
+
   if (FLAG_trace_wasm_decode_time) {
     decode_ms = decode_timer.Elapsed().InMillisecondsF();
   }
 
   base::ElapsedTimer compile_timer;
   if (FLAG_trace_wasm_decode_time) {
     compile_timer.Start();
   }
   // Run the compiler pipeline to generate machine code.
   CallDescriptor* descriptor =
@@ skipping 41 matching lines @@
         static_cast<int>(function.code_end_offset - function.code_start_offset),
         decode_ms, static_cast<int>(graph.NodeCount()), compile_ms);
   }
   return code;
 }
 
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8