Intel: Branch reordering and port arm EmitNumberUntagD() Improvement

src/x64/lithium-codegen-x64.cc

 // Copyright 2013 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 4605 matching lines @@
   __ SmiToInteger32(input, input);
 }
 
 
 void LCodeGen::EmitNumberUntagD(Register input_reg,
                                 XMMRegister result_reg,
                                 bool can_convert_undefined_to_nan,
                                 bool deoptimize_on_minus_zero,
                                 LEnvironment* env,
                                 NumberUntagDMode mode) {
-  Label load_smi, done;
+  Label convert, load_smi, done;
 
   if (mode == NUMBER_CANDIDATE_IS_ANY_TAGGED) {
     // Smi check.
     __ JumpIfSmi(input_reg, &load_smi, Label::kNear);
 
     // Heap number map check.
     __ CompareRoot(FieldOperand(input_reg, HeapObject::kMapOffset),
                    Heap::kHeapNumberMapRootIndex);
-    if (!can_convert_undefined_to_nan) {
+
+    // On x64 it is safe to load at heap number offset before evaluating the map
+    // check, since all heap objects are at least two words long.
+    __ movsd(result_reg, FieldOperand(input_reg, HeapNumber::kValueOffset));
+
+    if (can_convert_undefined_to_nan) {
+      __ j(not_equal, &convert);
+    } else {
       DeoptimizeIf(not_equal, env);
-    } else {
-      Label heap_number, convert;
-      __ j(equal, &heap_number, Label::kNear);
+    }
 
-      // Convert undefined (and hole) to NaN. Compute NaN as 0/0.
-      __ CompareRoot(input_reg, Heap::kUndefinedValueRootIndex);
-      DeoptimizeIf(not_equal, env);
-
-      __ bind(&convert);
-      __ xorps(result_reg, result_reg);
-      __ divsd(result_reg, result_reg);
-      __ jmp(&done, Label::kNear);
-
-      __ bind(&heap_number);
-    }
-    // Heap number to XMM conversion.
-    __ movsd(result_reg, FieldOperand(input_reg, HeapNumber::kValueOffset));
     if (deoptimize_on_minus_zero) {
       XMMRegister xmm_scratch = xmm0;
       __ xorps(xmm_scratch, xmm_scratch);
       __ ucomisd(xmm_scratch, result_reg);
       __ j(not_equal, &done, Label::kNear);
       __ movmskpd(kScratchRegister, result_reg);
       __ testq(kScratchRegister, Immediate(1));
       DeoptimizeIf(not_zero, env);
     }
     __ jmp(&done, Label::kNear);
+
+    if (can_convert_undefined_to_nan) {
+      __ bind(&convert);
+
+      // Convert undefined (and hole) to NaN. Compute NaN as 0/0.
+      __ CompareRoot(input_reg, Heap::kUndefinedValueRootIndex);
+      DeoptimizeIf(not_equal, env);
+
+      __ xorps(result_reg, result_reg);
+      __ divsd(result_reg, result_reg);
+      __ jmp(&done, Label::kNear);
+    }
   } else {
     ASSERT(mode == NUMBER_CANDIDATE_IS_SMI);
   }
 
   // Smi to XMM conversion
   __ bind(&load_smi);
   __ SmiToInteger32(kScratchRegister, input_reg);
   __ Cvtlsi2sd(result_reg, kScratchRegister);
   __ bind(&done);
 }
@@ skipping 819 matching lines @@
                                FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64