Rework SHOW_MEMORY

closes #10

Internal.h

@@ -40,13 +40,39 @@ operator<=>(const std::span<const uint8_t> &lhs,
 
 // GCOVR_EXCL_START
 
+#if SHOW_MEMORY
+#ifdef __APPLE__
+#include <malloc/malloc.h>
+#endif
+inline int64_t mallocBytes = 0;
+inline int64_t peakMallocBytes = 0;
+#endif
+
+// malloc that aborts on OOM and thus always returns a non-null pointer
 __attribute__((always_inline)) inline void *safe_malloc(size_t s) {
+#if SHOW_MEMORY
+  mallocBytes += s;
+  if (mallocBytes > peakMallocBytes) {
+    peakMallocBytes = mallocBytes;
+  }
+#endif
   if (void *p = malloc(s)) {
     return p;
   }
   abort();
 }
 
+// There's nothing safer about this than free. Only called safe_free for
+// symmetry with safe_malloc.
+__attribute__((always_inline)) inline void safe_free(void *p) {
+#if SHOW_MEMORY
+#ifdef __APPLE__
+  mallocBytes -= malloc_size(p);
+#endif
+#endif
+  free(p);
+}
+
 // ==================== BEGIN ARENA IMPL ====================
 
 /// Group allocations with similar lifetimes to amortize the cost of malloc/free