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

src/compiler/linkage.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_LINKAGE_H_
 #define V8_COMPILER_LINKAGE_H_
 
 #include "src/base/flags.h"
 #include "src/compiler/frame.h"
 #include "src/compiler/operator.h"
@@ skipping 144 matching lines @@
     kHasExceptionHandler = 1u << 1,
     kHasLocalCatchHandler = 1u << 2,
     kSupportsTailCalls = 1u << 3,
     kCanUseRoots = 1u << 4,
     // (arm64 only) native stack should be used for arguments.
     kUseNativeStack = 1u << 5,
     // (arm64 only) call instruction has to restore JSSP or CSP.
     kRestoreJSSP = 1u << 6,
     kRestoreCSP = 1u << 7,
     // Causes the code generator to initialize the root register.
-    kInitializeRootRegister = 1u << 8
+    kInitializeRootRegister = 1u << 8,
+    // Does not ever try to allocate space on our heap.
+    kNoAllocate = 1u << 9
   };
   typedef base::Flags<Flag> Flags;
 
   CallDescriptor(Kind kind, MachineType target_type, LinkageLocation target_loc,
                  const MachineSignature* machine_sig,
                  LocationSignature* location_sig, size_t stack_param_count,
                  Operator::Properties properties,
                  RegList callee_saved_registers,
                  RegList callee_saved_fp_registers, Flags flags,
                  const char* debug_name = "")
@@ skipping 225 matching lines @@
   CallDescriptor* const incoming_;
 
   DISALLOW_COPY_AND_ASSIGN(Linkage);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_LINKAGE_H_