libexpr: simplify HAVE_BOEHMGC ifdefs

if we define a TraceableAllocator at all times and use that in places
that want maybe-traceable allocation we can simplify things a lot. we
also unconditionally allocate cache root pointers for Value and Env-1
caches, even though we don't need them without gc (they're so cheap).
defaulting to `std::allocator` without gc recovers previous behavior.

Change-Id: I236da8c3b0669b40cdfe355ec3ec4e764d096074

lix/libcmd/command.cc

@@ -105,15 +105,9 @@ ref<Store> EvalCommand::getEvalStore()
 ref<eval_cache::CachingEvalState> EvalCommand::getEvalState()
 {
     if (!evalState) {
-        evalState =
-            #if HAVE_BOEHMGC
-            std::allocate_shared<eval_cache::CachingEvalState>(traceable_allocator<EvalState>(),
-                searchPath, getEvalStore(), getStore())
-            #else
-            std::make_shared<eval_cache::CachingEvalState>(
-                searchPath, getEvalStore(), getStore())
-            #endif
-            ;
+        evalState = std::allocate_shared<eval_cache::CachingEvalState>(
+            TraceableAllocator<EvalState>(), searchPath, getEvalStore(), getStore()
+        );
 
         evalState->repair = repair;
 

lix/libcmd/repl.cc

@@ -181,11 +181,7 @@ struct NixRepl
      * Note: This is `shared_ptr` to avoid garbage collection.
      */
     std::shared_ptr<Value *> replOverlaysEvalFunction =
-    #if HAVE_BOEHMGC
-        std::allocate_shared<Value *>(traceable_allocator<Value *>(), nullptr);
-    #else
-        std::make_shared<Value *>(nullptr);
-    #endif
+        std::allocate_shared<Value *>(TraceableAllocator<Value *>(), nullptr);
 
     /**
      * Get the `info` AttrSet that's passed as the first argument to each

lix/libexpr/eval.cc

@@ -51,11 +51,7 @@ namespace nix {
 
 RootValue allocRootValue(Value * v)
 {
-#if HAVE_BOEHMGC
-    return std::allocate_shared<Value *>(traceable_allocator<Value *>(), v);
-#else
-    return std::make_shared<Value *>(v);
-#endif
+    return std::allocate_shared<Value *>(TraceableAllocator<Value *>(), v);
 }
 
 // Pretty print types for assertion errors
@@ -254,10 +250,8 @@ StaticSymbols::StaticSymbols(SymbolTable & symbols)
 }
 
 EvalMemory::EvalMemory()
-#if HAVE_BOEHMGC
-    : valueAllocCache(std::allocate_shared<void *>(traceable_allocator<void *>(), nullptr))
-    , env1AllocCache(std::allocate_shared<void *>(traceable_allocator<void *>(), nullptr))
-#endif
+    : valueAllocCache(std::allocate_shared<void *>(TraceableAllocator<void *>(), nullptr))
+    , env1AllocCache(std::allocate_shared<void *>(TraceableAllocator<void *>(), nullptr))
 {
     assert(libexprInitialised);
 }

lix/libexpr/eval.hh

@@ -216,7 +216,6 @@ struct StaticSymbols
 
 class EvalMemory
 {
-#if HAVE_BOEHMGC
     /**
      * Allocation cache for GC'd Value objects.
      */
@@ -226,7 +225,6 @@ class EvalMemory
      * Allocation cache for size-1 Env objects.
      */
     std::shared_ptr<void *> env1AllocCache;
-#endif
 
 public:
     struct Statistics

lix/libexpr/gc-alloc.hh

@@ -13,8 +13,6 @@
 #include "lix/libutil/checked-arithmetic.hh"
 
 #if HAVE_BOEHMGC
-#include <functional> // std::less
-#include <utility> // std::pair
 #define GC_INCLUDE_NEW
 #include <gc/gc.h>
 #include <gc/gc_allocator.h>
@@ -32,25 +30,8 @@
 namespace nix
 {
 
-/// Alias for std::map which uses BoehmGC's allocator conditional on this Lix
-/// build having GC enabled.
-template<typename KeyT, typename ValueT>
-using GcMap = std::map<
-    KeyT,
-    ValueT,
-    std::less<KeyT>,
-    traceable_allocator<std::pair<KeyT const, ValueT>>
->;
-
-/// Alias for std::vector which uses BoehmGC's allocator conditional on this Lix
-/// build having GC enabled.
-template<typename ItemT>
-using GcVector = std::vector<ItemT, traceable_allocator<ItemT>>;
-
-/// Alias for std::list which uses BoehmGC's allocator conditional on this Lix
-/// build having GC enabled.
-template<typename ItemT>
-using GcList = std::list<ItemT, traceable_allocator<ItemT>>;
+template<typename T>
+using TraceableAllocator = traceable_allocator<T>;
 
 }
 
@@ -71,20 +52,8 @@ using GcList = std::list<ItemT, traceable_allocator<ItemT>>;
 namespace nix
 {
 
-/// Alias for std::map which uses BoehmGC's allocator conditional on this Lix
-/// build having GC enabled.
-template<typename KeyT, typename ValueT>
-using GcMap = std::map<KeyT, ValueT>;
-
-/// Alias for std::vector which uses BoehmGC's allocator conditional on this Lix
-/// build having GC enabled.
-template<typename ItemT>
-using GcVector = std::vector<ItemT>;
-
-/// Alias for std::list which uses BoehmGC's allocator conditional on this Lix
-/// build having GC enabled.
-template<typename ItemT>
-using GcList = std::list<ItemT>;
+template<typename T>
+using TraceableAllocator = std::allocator<T>;
 
 }
 
@@ -93,6 +62,26 @@ using GcList = std::list<ItemT>;
 namespace nix
 {
 
+/// Alias for std::map which uses BoehmGC's allocator conditional on this Lix
+/// build having GC enabled.
+template<typename KeyT, typename ValueT>
+using GcMap = std::map<
+    KeyT,
+    ValueT,
+    std::less<KeyT>,
+    TraceableAllocator<std::pair<KeyT const, ValueT>>
+>;
+
+/// Alias for std::vector which uses BoehmGC's allocator conditional on this Lix
+/// build having GC enabled.
+template<typename ItemT>
+using GcVector = std::vector<ItemT, TraceableAllocator<ItemT>>;
+
+/// Alias for std::list which uses BoehmGC's allocator conditional on this Lix
+/// build having GC enabled.
+template<typename ItemT>
+using GcList = std::list<ItemT, TraceableAllocator<ItemT>>;
+
 [[gnu::always_inline]]
 inline void * gcAllocBytes(size_t n)
 {

lix/libexpr/gc-small-vector.hh

@@ -1,17 +1,9 @@
 #pragma once
 ///@file
 
+#include "gc-alloc.hh"
 #include <boost/container/small_vector.hpp>
 
-#if HAVE_BOEHMGC
-
-#define GC_INCLUDE_NEW
-#include <gc/gc.h>
-#include <gc/gc_cpp.h>
-#include <gc/gc_allocator.h>
-
-#endif
-
 namespace nix {
 
 struct Value;
@@ -19,13 +11,8 @@ struct Value;
 /**
  * A GC compatible vector that may used a reserved portion of `nItems` on the stack instead of allocating on the heap.
  */
-#if HAVE_BOEHMGC
 template <typename T, size_t nItems>
-using SmallVector = boost::container::small_vector<T, nItems, traceable_allocator<T>>;
-#else
-template <typename T, size_t nItems>
-using SmallVector = boost::container::small_vector<T, nItems>;
-#endif
+using SmallVector = boost::container::small_vector<T, nItems, TraceableAllocator<T>>;
 
 /**
  * A vector of value pointers. See `SmallVector`.