Add int_map and use it to speed up sparse mem

riscv/devices.cc

@@ -92,7 +92,7 @@ bool mmio_plugin_device_t::store(reg_t addr, size_t len, const uint8_t* bytes)
 }
 
 mem_t::mem_t(reg_t size)
-  : sparse_memory_map(log2(size) + (size & (size-1) ? 1 : 0)), sz(size)
+  : sz(size)
 {
   if (size == 0 || size % PGSIZE != 0)
     throw std::runtime_error("memory size must be a positive multiple of 4 KiB");

riscv/int_map.h

@@ -1,16 +1,15 @@
 #ifndef _RISCV_INT_MAP_H
 #define _RISCV_INT_MAP_H
 
+#include "common.h"
 #include <cstdint>
 #include <climits>
-#include <cassert>
 
 // Like std::map, but keys are integers
-template<typename K, typename V, int lg_radix = 11>
+template<typename K, typename V, int lg_n = sizeof(K) * CHAR_BIT, int lg_radix = 11>
 class int_map {
  public:
-  int_map(int lg_n = sizeof(K) * CHAR_BIT)
-    : lg_n(lg_n)
+  int_map()
   {
     memset(array, 0, sizeof(array));
   }
@@ -24,15 +23,14 @@ class int_map {
       return reinterpret_cast<V*>(&array[idx]);
     }
 
-    if (array[idx] == nullptr)
-      array[idx] = new int_map<K, V, lg_radix>(lg_n - lg_radix);
+    if (unlikely(array[idx] == nullptr))
+      array[idx] = new int_map<K, V, lg_n < 0 ? 0 : lg_n - lg_radix, lg_radix>;
 
     return array[idx]->lookup(k >> lg_radix);
   }
 
  private:
-  int lg_n;
-  int_map<K, V, lg_radix>* array[size_t(1) << lg_radix];
+  int_map<K, V, lg_n < 0 ? 0 : lg_n - lg_radix, lg_radix>* array[size_t(1) << lg_radix];
 };
 
 #endif