[crankshaft] Fragmentation-free allocation folding.

src/crankshaft/x64/lithium-x64.h

Index: src/crankshaft/x64/lithium-x64.h
diff --git a/src/crankshaft/x64/lithium-x64.h b/src/crankshaft/x64/lithium-x64.h
index 1feba4bf208508f0e97780e617538204d8634010..f89c51dd0aeb1ef84c62c50e91e4d013f52a574a 100644
--- a/src/crankshaft/x64/lithium-x64.h
+++ b/src/crankshaft/x64/lithium-x64.h
@@ -67,6 +67,7 @@ class LCodeGen;
   V(Drop)                                    \
   V(DummyUse)                                \
   V(Dummy)                                   \
+  V(FastAllocate)                            \
   V(FlooringDivByConstI)                     \
   V(FlooringDivByPowerOf2I)                  \
   V(FlooringDivI)                            \
@@ -2385,6 +2386,19 @@ class LAllocate final : public LTemplateInstruction<1, 2, 1> {
   DECLARE_HYDROGEN_ACCESSOR(Allocate)
 };
 
+class LFastAllocate final : public LTemplateInstruction<1, 1, 1> {
+ public:
+  LFastAllocate(LOperand* size, LOperand* temp) {
+    inputs_[0] = size;
+    temps_[0] = temp;
+  }
+
+  LOperand* size() const { return inputs_[0]; }
+  LOperand* temp() { return temps_[0]; }
+
+  DECLARE_CONCRETE_INSTRUCTION(FastAllocate, "fast-allocate")
+  DECLARE_HYDROGEN_ACCESSOR(Allocate)
+};
 
 class LTypeof final : public LTemplateInstruction<1, 2, 0> {
  public: