ARM: Use loop to initialize locals when optimizing for size.

src/arm/full-codegen-arm.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
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@@ skipping 150 matching lines @@
 
   info->set_prologue_offset(masm_->pc_offset());
   __ Prologue(BUILD_FUNCTION_FRAME);
   info->AddNoFrameRange(0, masm_->pc_offset());
 
   { Comment cmnt(masm_, "[ Allocate locals");
     int locals_count = info->scope()->num_stack_slots();
     // Generators allocate locals, if any, in context slots.
     ASSERT(!info->function()->is_generator() || locals_count == 0);
     if (locals_count > 0) {
-      __ LoadRoot(ip, Heap::kUndefinedValueRootIndex);
-      for (int i = 0; i < locals_count; i++) {
+      // Emit a loop to initialize stack cells for locals when optimizing for
+      // size. Otherwise, unroll the loop for maximum performance.
+      if (FLAG_optimize_for_size && locals_count > 4) {
+        Label loop;
+        __ mov(r2, Operand(locals_count));
+        __ LoadRoot(ip, Heap::kUndefinedValueRootIndex);

[vincent.belliard.fr, 2013/10/30 08:45:02]

The two LoadRoot can be factorized before the if.

[Benedikt Meurer, 2013/10/30 08:46:53]

Hm, no, I think the mov(r2, Operand(locals_count)) could clobber ip.

[vincent.belliard.fr, 2013/10/30 08:53:56]

We can use an other register to load undefined (for example r9).

+        __ bind(&loop);
+        __ sub(r2, r2, Operand(1), SetCC);
         __ push(ip);
+        __ b(&loop, ne);
+      } else {
+        __ LoadRoot(ip, Heap::kUndefinedValueRootIndex);
+        for (int i = 0; i < locals_count; i++) {
+          __ push(ip);
+        }
       }
     }
   }
 
   bool function_in_register = true;
 
   // Possibly allocate a local context.
   int heap_slots = info->scope()->num_heap_slots() - Context::MIN_CONTEXT_SLOTS;
   if (heap_slots > 0) {
     // Argument to NewContext is the function, which is still in r1.
@@ skipping 4775 matching lines @@
   ASSERT(Memory::uint32_at(interrupt_address_pointer) ==
          reinterpret_cast<uint32_t>(
              isolate->builtins()->OsrAfterStackCheck()->entry()));
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM