From 145445f218a224e2aaef763e027d94b7b49ba0e4 Mon Sep 17 00:00:00 2001
From: tastynoob <934348725@qq.com>
Date: Wed, 13 Dec 2023 18:18:51 +0800
Subject: [PATCH] Update diff memcpy with COW optimization

---
 difftest/difftest.cc | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/difftest/difftest.cc b/difftest/difftest.cc
index e20405f6e7..8dc3dccd7e 100644
--- a/difftest/difftest.cc
+++ b/difftest/difftest.cc
@@ -245,9 +245,19 @@ void DifftestRef::set_regs(diff_context_t *ctx, bool on_demand) {
 
 void DifftestRef::memcpy_from_dut(reg_t dest, void* src, size_t n) {
   while (n) {
-    char *base = sim->addr_to_mem(dest);
+    bool is_zero = true;
+    for (int i=0; i < (PGSIZE/sizeof(uint64_t)); i++) {
+      if (((uint64_t*)src)[i] != 0) {
+        is_zero = false;
+        break;
+      }
+    }
+
     size_t n_bytes = (n > PGSIZE) ? PGSIZE : n;
-    memcpy(base, src, n_bytes);
+    if (!is_zero) {
+      char *base = sim->addr_to_mem(dest);
+      memcpy(base, src, n_bytes);
+    }
     dest += PGSIZE;
     src = (char *)src + PGSIZE;
     n -= n_bytes;