VM: Avoid allocating strings when disassembling code.

runtime/vm/disassembler.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/disassembler.h"
 
 #include "vm/assembler.h"
 #include "vm/deopt_instructions.h"
 #include "vm/globals.h"
 #include "vm/il_printer.h"
@@ skipping 87 matching lines @@
   jsarr_.AddValue(p);
   jsarr_.AddValueNull();
   free(p);
 }
 
 
 void Disassembler::Disassemble(uword start,
                                uword end,
                                DisassemblyFormatter* formatter,
                                const Code& code) {
+  NoSafepointScope no_safepoint;
   const Code::Comments& comments =
       code.IsNull() ? Code::Comments::New(0) : code.comments();
   ASSERT(formatter != NULL);
   char hex_buffer[kHexadecimalBufferSize];  // Instruction in hexadecimal form.
   char human_buffer[kUserReadableBufferSize];  // Human-readable instruction.
   uword pc = start;
   intptr_t comment_finger = 0;
   GrowableArray<Function*> inlined_functions;
   while (pc < end) {
     const intptr_t offset = pc - start;
@@ skipping 40 matching lines @@
                                   sizeof(human_buffer),
                                   object,
                                   pc);
     pc += instruction_length;
   }
 }
 
 
 void Disassembler::DisassembleCodeHelper(
     const char* function_fullname, const Code& code, bool optimized) {
+  LocalVarDescriptors& var_descriptors = LocalVarDescriptors::Handle();
+  if (FLAG_print_variable_descriptors) {
+    // This flag is not on by default, and for debugging purposes only.
+    // Since this may allocate, do it outside the NoSafepointScope.
+    var_descriptors = code.GetLocalVarDescriptors();
+  }
+  NoSafepointScope no_safepoint;
   THR_Print("Code for %sfunction '%s' {\n",
             optimized ? "optimized " : "",
             function_fullname);
   code.Disassemble();
   THR_Print("}\n");
 
 #if defined(TARGET_ARCH_IA32)
   THR_Print("Pointer offsets for function: {\n");
   // Pointer offsets are stored in descending order.
   Object& obj = Object::Handle();
@@ skipping 47 matching lines @@
     for (intptr_t i = 0; i < stackmap_table.Length(); ++i) {
       map ^= stackmap_table.At(i);
       THR_Print("%s\n", map.ToCString());
     }
   }
   THR_Print("}\n");
 
   if (FLAG_print_variable_descriptors) {
     THR_Print("Variable Descriptors for function '%s' {\n",
               function_fullname);
-    const LocalVarDescriptors& var_descriptors =
-        LocalVarDescriptors::Handle(code.GetLocalVarDescriptors());
     intptr_t var_desc_length =
         var_descriptors.IsNull() ? 0 : var_descriptors.Length();
     String& var_name = String::Handle();
     for (intptr_t i = 0; i < var_desc_length; i++) {
       var_name = var_descriptors.GetName(i);
       RawLocalVarDescriptors::VarInfo var_info;
       var_descriptors.GetInfo(i, &var_info);
       const int8_t kind = var_info.kind();
       if (kind == RawLocalVarDescriptors::kSavedCurrentContext) {
         THR_Print("  saved current CTX reg offset %d\n", var_info.index());
@@ skipping 29 matching lines @@
     Code& code = Code::Handle();
     for (intptr_t i = 0; i < table.Length();
         i += Code::kSCallTableEntryLength) {
       offset ^= table.At(i + Code::kSCallTableOffsetEntry);
       function ^= table.At(i + Code::kSCallTableFunctionEntry);
       code ^= table.At(i + Code::kSCallTableCodeEntry);
       if (function.IsNull()) {
         Class& cls = Class::Handle();
         cls ^= code.owner();
         if (cls.IsNull()) {
-          const String& code_name = String::Handle(code.Name());
           THR_Print("  0x%" Px ": %s, %p\n",
               start + offset.Value(),
-              code_name.ToCString(),
+              code.Name(),
               code.raw());
         } else {
           THR_Print("  0x%" Px ": allocation stub for %s, %p\n",
               start + offset.Value(),
               cls.ToCString(),
               code.raw());
         }
       } else {
         THR_Print("  0x%" Px ": %s, %p\n",
             start + offset.Value(),
@@ skipping 20 matching lines @@
     const Function& function, bool optimized) {
   const char* function_fullname = function.ToFullyQualifiedCString();
   const Code& code = Code::Handle(function.unoptimized_code());
   DisassembleCodeHelper(function_fullname, code, optimized);
 }
 
 
 #endif  // !PRODUCT
 
 }  // namespace dart