[Local GC] Remove static fields from GC interface (#10566)

* Remove max_generation from GC interface

* [Local GC] Clean up the GC interface by removing all static fields
from it:
  1) gcHeapType is replaced by g_heap_type (EE side) and g_gc_heap_type
     (GC side), each of which is set on initialization. g_heap_type is
     read by the DAC to determine what kind of heap is being used.
  2) maxGeneration is not necessary due to the GC DAC changes.

* Rebase against master

* Comments and cleanup

* Use a heap allocation instead of alloca

* Code review feedback: remove a redundant cast and allocate generation count table once, on first use

* Address code review feedback: cache some calls to GetMaxGeneration

6 files changed, 20 insertions, 44 deletions

diff --git a/src/gc/gc.cpp b/src/gc/gc.cpp
index 515069b7c2..d8a59cd5e4 100644
--- a/src/gc/gc.cpp
+++ b/src/gc/gc.cpp
@@ -36946,10 +36946,7 @@ void PopulateDacVars(GcDacVars *gcDacVars)
     gcDacVars->build_variant = &g_build_variant;
     gcDacVars->gc_structures_invalid_cnt = const_cast<int32_t*>(&GCScan::m_GcStructuresInvalidCnt);
     gcDacVars->generation_size = sizeof(generation);
-#ifdef FEATURE_SVR_GC
-    gcDacVars->gc_heap_type = &IGCHeap::gcHeapType;
-#endif // FEATURE_SVR_GC
-    gcDacVars->max_gen = &IGCHeap::maxGeneration;
+    gcDacVars->max_gen = &g_max_generation;
 #ifndef MULTIPLE_HEAPS
     gcDacVars->mark_array = &gc_heap::mark_array;
     gcDacVars->ephemeral_heap_segment = reinterpret_cast<dac_heap_segment**>(&gc_heap::ephemeral_heap_segment);
diff --git a/src/gc/gc.h b/src/gc/gc.h
index ecb791f728..821b21ddb8 100644
--- a/src/gc/gc.h
+++ b/src/gc/gc.h
@@ -87,6 +87,7 @@ class IGCHeapInternal;
 
 /* misc defines */
 #define LARGE_OBJECT_SIZE ((size_t)(85000))
+#define max_generation 2
 
 #ifdef GC_CONFIG_DRIVEN
 #define MAX_GLOBAL_GC_MECHANISMS_COUNT 6
@@ -110,6 +111,8 @@ extern "C" uint32_t* g_gc_card_bundle_table;
 extern "C" uint32_t* g_gc_card_table;
 extern "C" uint8_t* g_gc_lowest_address;
 extern "C" uint8_t* g_gc_highest_address;
+extern "C" GCHeapType g_gc_heap_type;
+extern "C" uint32_t g_max_generation;
 
 ::IGCHandleTable*  CreateGCHandleTable();
 
@@ -219,7 +222,7 @@ public:
 
     unsigned GetMaxGeneration()
     {
-        return IGCHeap::maxGeneration;
+        return max_generation;
     }
 
     bool IsValidSegmentSize(size_t cbSize)
@@ -235,8 +238,6 @@ public:
 
     BOOL IsLargeObject(MethodTable *mt)
     {
-        WRAPPER_NO_CONTRACT;
-
         return mt->GetBaseSize() >= LARGE_OBJECT_SIZE;
     }
 
@@ -270,18 +271,15 @@ extern IGCHandleTable* g_theGCHandleTable;
 #ifndef DACCESS_COMPILE
 inline bool IsGCInProgress(bool bConsiderGCStart = false)
 {
-    WRAPPER_NO_CONTRACT;
-
     return g_theGCHeap != nullptr ? g_theGCHeap->IsGCInProgressHelper(bConsiderGCStart) : false;
 }
 #endif // DACCESS_COMPILE
 
 inline bool IsServerHeap()
 {
-    LIMITED_METHOD_CONTRACT;
 #ifdef FEATURE_SVR_GC
-    _ASSERTE(IGCHeap::gcHeapType != IGCHeap::GC_HEAP_INVALID);
-    return (IGCHeap::gcHeapType == IGCHeap::GC_HEAP_SVR);
+    assert(g_gc_heap_type != GC_HEAP_INVALID);
+    return g_gc_heap_type == GC_HEAP_SVR;
 #else // FEATURE_SVR_GC
     return false;
 #endif // FEATURE_SVR_GC
diff --git a/src/gc/gccommon.cpp b/src/gc/gccommon.cpp
index 8f6d1ac2be..1cd3c824ac 100644
--- a/src/gc/gccommon.cpp
+++ b/src/gc/gccommon.cpp
@@ -14,12 +14,6 @@
 #include "gcenv.h"
 #include "gc.h"
 
-#ifdef FEATURE_SVR_GC
-SVAL_IMPL_INIT(uint32_t,IGCHeap,gcHeapType,IGCHeap::GC_HEAP_INVALID);
-#endif // FEATURE_SVR_GC
-
-SVAL_IMPL_INIT(uint32_t,IGCHeap,maxGeneration,2);
-
 IGCHeapInternal* g_theGCHeap;
 IGCHandleTable* g_theGCHandleTable;
 
@@ -47,6 +41,8 @@ uint32_t* g_gc_card_bundle_table;
 
 uint8_t* g_gc_lowest_address  = 0;
 uint8_t* g_gc_highest_address = 0;
+GCHeapType g_gc_heap_type = GC_HEAP_INVALID;
+uint32_t g_max_generation = max_generation;
 
 #ifdef GC_CONFIG_DRIVEN
 void record_global_mechanism (int mech_index)
@@ -122,9 +118,9 @@ void InitializeHeapType(bool bServerHeap)
 {
     LIMITED_METHOD_CONTRACT;
 #ifdef FEATURE_SVR_GC
-    IGCHeap::gcHeapType = bServerHeap ? IGCHeap::GC_HEAP_SVR : IGCHeap::GC_HEAP_WKS;
+    g_gc_heap_type = bServerHeap ? GC_HEAP_SVR : GC_HEAP_WKS;
 #ifdef WRITE_BARRIER_CHECK
-    if (IGCHeap::gcHeapType == IGCHeap::GC_HEAP_SVR)
+    if (g_gc_heap_type == GC_HEAP_SVR)
     {
         g_GCShadow = 0;
         g_GCShadowEnd = 0;
@@ -163,9 +159,9 @@ bool InitializeGarbageCollector(IGCToCLR* clrToGC, IGCHeap** gcHeap, IGCHandleTa
     }
 
 #ifdef FEATURE_SVR_GC
-    assert(IGCHeap::gcHeapType != IGCHeap::GC_HEAP_INVALID);
+    assert(g_gc_heap_type != GC_HEAP_INVALID);
 
-    if (IGCHeap::gcHeapType == IGCHeap::GC_HEAP_SVR)
+    if (g_gc_heap_type == GC_HEAP_SVR)
     {
         heap = SVR::CreateGCHeap();
         SVR::PopulateDacVars(gcDacVars);
diff --git a/src/gc/gcinterface.dac.h b/src/gc/gcinterface.dac.h
index 84c8ffb36a..647101fa1f 100644
--- a/src/gc/gcinterface.dac.h
+++ b/src/gc/gcinterface.dac.h
@@ -18,12 +18,6 @@
 #define MAX_GLOBAL_GC_MECHANISMS_COUNT 6
 #define NUMBERGENERATIONS              4
 
-// TODO(segilles) - Implement this scheme for Server GC
-namespace SVR {
-    class heap_segment;
-    class gc_heap;
-}
-
 // Analogue for the GC heap_segment class, containing information regarding a single
 // heap segment.
 class dac_heap_segment {
diff --git a/src/gc/gcinterface.dacvars.def b/src/gc/gcinterface.dacvars.def
index f9c2078ee3..b788079dcb 100644
--- a/src/gc/gcinterface.dacvars.def
+++ b/src/gc/gcinterface.dacvars.def
@@ -38,7 +38,6 @@ GC_DAC_VAR        (uint8_t,               build_variant)
 GC_DAC_VAR        (bool,                  built_with_svr)
 GC_DAC_ARRAY_VAR  (size_t,                gc_global_mechanisms)
 GC_DAC_ARRAY_VAR  (dac_generation,        generation_table)
-GC_DAC_VAR        (uint32_t,              gc_heap_type)
 GC_DAC_VAR        (uint32_t,              max_gen)
 GC_DAC_PTR_VAR    (uint32_t,              mark_array)
 GC_DAC_VAR        (c_gc_state,            current_c_gc_state)
diff --git a/src/gc/gcinterface.h b/src/gc/gcinterface.h
index b5a9e0e8f9..66d8b31a53 100644
--- a/src/gc/gcinterface.h
+++ b/src/gc/gcinterface.h
@@ -163,8 +163,6 @@ struct segment_info
 // one for the object header, and one for the first field in the object.
 #define min_obj_size ((sizeof(uint8_t*) + sizeof(uintptr_t) + sizeof(size_t)))
 
-#define max_generation 2
-
 // The bit shift used to convert a memory address into an index into the
 // Software Write Watch table.
 #define SOFTWARE_WRITE_WATCH_AddressToTableByteIndexShift 0xc
@@ -379,6 +377,13 @@ typedef enum
     HNDTYPE_WEAK_WINRT   = 9
 } HandleType;
 
+typedef enum
+{
+    GC_HEAP_INVALID = 0,
+    GC_HEAP_WKS     = 1,
+    GC_HEAP_SVR     = 2
+} GCHeapType;
+
 typedef bool (* walk_fn)(Object*, void*);
 typedef void (* gen_walk_fn)(void* context, int generation, uint8_t* range_start, uint8_t* range_end, uint8_t* range_reserved);
 typedef void (* record_surv_fn)(uint8_t* begin, uint8_t* end, ptrdiff_t reloc, void* context, bool compacting_p, bool bgc_p);
@@ -729,19 +734,6 @@ public:
 
     IGCHeap() {}
     virtual ~IGCHeap() {}
-
-    typedef enum
-    {
-        GC_HEAP_INVALID = 0,
-        GC_HEAP_WKS     = 1,
-        GC_HEAP_SVR     = 2
-    } GC_HEAP_TYPE;
-
-#ifdef FEATURE_SVR_GC
-    SVAL_DECL(uint32_t, gcHeapType);
-#endif
-
-    SVAL_DECL(uint32_t, maxGeneration);
 };
 
 #ifdef WRITE_BARRIER_CHECK