[turbofan] Initial version of allocation folding and write barrier elimination.

src/x64/builtins-x64.cc

Index: src/x64/builtins-x64.cc
diff --git a/src/x64/builtins-x64.cc b/src/x64/builtins-x64.cc
index a14fdf5b184a324196b06d39472a72fbe601d37d..dc8cd74956258dd4d59a6786d8b76f95ed11dd8b 100644
--- a/src/x64/builtins-x64.cc
+++ b/src/x64/builtins-x64.cc
@@ -2048,11 +2048,6 @@ void Builtins::Generate_AllocateInNewSpace(MacroAssembler* masm) {
   //  -- rdx    : requested object size (untagged)
   //  -- rsp[0] : return address
   // -----------------------------------
-  Label runtime;
-  __ Allocate(rdx, rax, rcx, rdi, &runtime, NO_ALLOCATION_FLAGS);
-  __ Ret();
-
-  __ bind(&runtime);
   __ Integer32ToSmi(rdx, rdx);
   __ PopReturnAddressTo(rcx);
   __ Push(rdx);
@@ -2067,11 +2062,6 @@ void Builtins::Generate_AllocateInOldSpace(MacroAssembler* masm) {
   //  -- rdx    : requested object size (untagged)
   //  -- rsp[0] : return address
   // -----------------------------------
-  Label runtime;
-  __ Allocate(rdx, rax, rcx, rdi, &runtime, PRETENURE);
-  __ Ret();
-
-  __ bind(&runtime);
   __ Integer32ToSmi(rdx, rdx);
   __ PopReturnAddressTo(rcx);
   __ Push(rdx);