Use immediate add when possible in space allocator

src/arm/macro-assembler-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.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1552 matching lines @@
       reinterpret_cast<intptr_t>(new_space_allocation_top.address());
   intptr_t limit =
       reinterpret_cast<intptr_t>(new_space_allocation_limit.address());
   ASSERT((limit - top) == kPointerSize);
   ASSERT(result.code() < ip.code());
 
   // Set up allocation top address and object size registers.
   Register topaddr = scratch1;
   Register obj_size_reg = scratch2;
   mov(topaddr, Operand(new_space_allocation_top));
-  mov(obj_size_reg, Operand(object_size));
+  Operand obj_size_operand = Operand(object_size);
+  if (!obj_size_operand.is_single_instruction(this)) {
+    // We are about to steal IP, so we need to load this value first
+    mov(obj_size_reg, obj_size_operand);
+  }
 
   // This code stores a temporary value in ip. This is OK, as the code below
   // does not need ip for implicit literal generation.
   if ((flags & RESULT_CONTAINS_TOP) == 0) {
     // Load allocation top into result and allocation limit into ip.
     ldm(ia, topaddr, result.bit() | ip.bit());
   } else {
     if (emit_debug_code()) {
       // Assert that result actually contains top on entry. ip is used
       // immediately below so this use of ip does not cause difference with
       // respect to register content between debug and release mode.
       ldr(ip, MemOperand(topaddr));
       cmp(result, ip);
       Check(eq, "Unexpected allocation top");
     }
     // Load allocation limit into ip. Result already contains allocation top.
     ldr(ip, MemOperand(topaddr, limit - top));
   }
 
   // Calculate new top and bail out if new space is exhausted. Use result
   // to calculate the new top.
-  add(scratch2, result, Operand(obj_size_reg), SetCC);
+  if (obj_size_operand.is_single_instruction(this)) {
+    // We can add the size as an immediate
+    add(scratch2, result, obj_size_operand, SetCC);
+  } else {
+    // Doesn't fit in an immediate, we have to use the register
+    add(scratch2, result, obj_size_reg, SetCC);
+  }
   b(cs, gc_required);
   cmp(scratch2, Operand(ip));
   b(hi, gc_required);
   str(scratch2, MemOperand(topaddr));
 
   // Tag object if requested.
   if ((flags & TAG_OBJECT) != 0) {
     add(result, result, Operand(kHeapObjectTag));
   }
 }
@@ skipping 2248 matching lines @@
 void CodePatcher::EmitCondition(Condition cond) {
   Instr instr = Assembler::instr_at(masm_.pc_);
   instr = (instr & ~kCondMask) | cond;
   masm_.emit(instr);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM