make SIP not on by default (#73434)

I'm seeing with SIP the heap size can increase noticeably because we don't compact the SIP regions, for workload that rarely ever does blocking gen2s. so I'm making these not on by default but can be turned on with the GCEnableSpecialRegions config.

there are a few methods that are currently compiled for both segments and regions but are only used for segments so made those only compiled for segments.

src/coreclr/gc/gc.cpp

@@ -2660,7 +2660,9 @@ bool          gc_heap::use_large_pages_p = 0;
 #ifdef HEAP_BALANCE_INSTRUMENTATION
 size_t        gc_heap::last_gc_end_time_us = 0;
 #endif //HEAP_BALANCE_INSTRUMENTATION
-#ifndef USE_REGIONS
+#ifdef USE_REGIONS
+bool          gc_heap::enable_special_regions_p = false;
+#else //USE_REGIONS
 size_t        gc_heap::min_segment_size = 0;
 size_t        gc_heap::min_uoh_segment_size = 0;
 #endif //!USE_REGIONS
@@ -5622,7 +5624,6 @@ gc_heap::soh_get_segment_to_expand()
     dprintf (GTC_LOG, ("(gen%d)creating new segment %Ix", settings.condemned_generation, result));
     return result;
 }
-#endif //!USE_REGIONS
 
 //returns 0 in case of allocation failure
 heap_segment*
@@ -5768,6 +5769,7 @@ void gc_heap::release_segment (heap_segment* sg)
     FIRE_EVENT(GCFreeSegment_V1, heap_segment_mem(sg));
     virtual_free (sg, (uint8_t*)heap_segment_reserved (sg)-(uint8_t*)sg, sg);
 }
+#endif //!USE_REGIONS
 
 heap_segment* gc_heap::get_segment_for_uoh (int gen_number, size_t size
 #ifdef MULTIPLE_HEAPS
@@ -8886,6 +8888,7 @@ void gc_heap::set_fgm_result (failure_get_memory f, size_t s, BOOL loh_p)
 #endif //MULTIPLE_HEAPS
 }
 
+#ifndef USE_REGIONS
 //returns 0 for success, -1 otherwise
 // We are doing all the decommitting here because we want to make sure we have
 // enough memory to do so - if we do this during copy_brick_card_table and
@@ -9195,6 +9198,7 @@ int gc_heap::grow_brick_card_tables (uint8_t* start,
 
     return 0;
 }
+#endif //!USE_REGIONS
 
 //copy all of the arrays managed by the card table for a page aligned range
 void gc_heap::copy_brick_card_range (uint8_t* la, uint32_t* old_card_table,
@@ -11146,7 +11150,6 @@ void gc_heap::clear_region_info (heap_segment* region)
 }
 
 // Note that returning a region to free does not decommit.
-// REGIONS PERF TODO: should decommit if needed.
 void gc_heap::return_free_region (heap_segment* region)
 {
     gc_oh_num oh = heap_segment_oh (region);
@@ -30798,6 +30801,11 @@ void gc_heap::update_start_tail_regions (generation* gen,
 inline
 bool gc_heap::should_sweep_in_plan (heap_segment* region)
 {
+    if (!enable_special_regions_p)
+    {
+        return false;
+    }
+
     if (settings.reason == reason_induced_aggressive)
     {
         return false;
@@ -44328,6 +44336,7 @@ HRESULT GCHeap::Initialize()
     GCConfig::SetHeapCount(static_cast<int64_t>(nhp));
 
 #ifdef USE_REGIONS
+    gc_heap::enable_special_regions_p = (bool)GCConfig::GetGCEnableSpecialRegions();
     size_t gc_region_size = (size_t)GCConfig::GetGCRegionSize();
     if (!power_of_two_p(gc_region_size) || ((gc_region_size * nhp * 19) > gc_heap::regions_range))
     {

src/coreclr/gc/gcconfig.h

@@ -105,6 +105,7 @@ class GCConfigStringHolder
     INT_CONFIG   (GCTotalPhysicalMemory,     "GCTotalPhysicalMemory",     NULL,                                0,                  "Specifies what the GC should consider to be total physical memory")                      \
     INT_CONFIG   (GCRegionRange,             "GCRegionRange",             NULL,                                0,                  "Specifies the range for the GC heap")                                                    \
     INT_CONFIG   (GCRegionSize,              "GCRegionSize",              NULL,                                4194304,            "Specifies the size for a basic GC region")                                               \
+    INT_CONFIG   (GCEnableSpecialRegions,    "GCEnableSpecialRegions",    NULL,                                0,                  "Specifies to enable special handling some regions like SIP")                             \
     STRING_CONFIG(LogFile,                   "GCLogFile",                 NULL,                                                    "Specifies the name of the GC log file")                                                  \
     STRING_CONFIG(ConfigLogFile,             "GCConfigLogFile",           NULL,                                                    "Specifies the name of the GC config log file")                                           \
     INT_CONFIG   (BGCFLTuningEnabled,        "BGCFLTuningEnabled",        NULL,                                0,                  "Enables FL tuning")                                                                      \

src/coreclr/gc/gcpriv.h

@@ -1596,24 +1596,24 @@ class gc_heap
     static
     void get_card_table_element_sizes (uint8_t* start, uint8_t* end, size_t bookkeeping_sizes[total_bookkeeping_elements]);
 
+    static
+    void set_fgm_result (failure_get_memory f, size_t s, BOOL loh_p);
+
 #ifdef USE_REGIONS
     static
     bool on_used_changed (uint8_t* left);
 
     static
     bool inplace_commit_card_table (uint8_t* from, uint8_t* to);
-#endif //USE_REGIONS
-
-    static
-    void set_fgm_result (failure_get_memory f, size_t s, BOOL loh_p);
-
+#else //USE_REGIONS
     static
     int grow_brick_card_tables (uint8_t* start,
                                 uint8_t* end,
                                 size_t size,
                                 heap_segment* new_seg,
                                 gc_heap* hp,
                                 BOOL loh_p);
+#endif //USE_REGIONS
 
     PER_HEAP_ISOLATED
     BOOL is_mark_set (uint8_t* o);
@@ -2001,11 +2001,11 @@ class gc_heap
 #ifndef USE_REGIONS
     PER_HEAP
     heap_segment* soh_get_segment_to_expand();
-#endif //!USE_REGIONS
     PER_HEAP
     heap_segment* get_segment (size_t size, gc_oh_num oh);
     PER_HEAP_ISOLATED
     void release_segment (heap_segment* sg);
+#endif //!USE_REGIONS
     PER_HEAP_ISOLATED
     void seg_mapping_table_add_segment (heap_segment* seg, gc_heap* hp);
     PER_HEAP_ISOLATED
@@ -4040,7 +4040,10 @@ class gc_heap
     size_t last_gc_end_time_us;
 #endif //HEAP_BALANCE_INSTRUMENTATION
 
-#ifndef USE_REGIONS
+#ifdef USE_REGIONS
+    PER_HEAP_ISOLATED
+    bool enable_special_regions_p;
+#else //USE_REGIONS
     PER_HEAP_ISOLATED
     size_t min_segment_size;