difftest: allow early store events for the current instruction (#379)

Previously we require store events to be updated after the store
instruction is committed. This commit further allows early store
events for the current to-be-committed instruction(s). The next
commit event, which contains a group of instructions will flush
the store queue and check all updated stores. It's worth noting
store events are allowed only for the current pending commit
instructions. Store events for future instructions (not committed
in the next commit event) will make the co-simulation fail.

Co-authored-by: Anzooooo <[email protected]>

src/test/csrc/difftest/difftest.cpp

@@ -250,9 +250,12 @@ int Difftest::step() {
     return 1;
   }
   do_first_instr_commit();
-  if (do_store_check()) {
-    return 1;
-  }
+
+  // Each cycle is checked for an store event, and recorded in queue.
+  // It is checked every time an instruction is committed and queue has content.
+#ifdef CONFIG_DIFFTEST_STOREEVENT
+  store_event_record();
+#endif
 
 #ifdef DEBUG_GOLDENMEM
   if (do_golden_memory_update()) {
@@ -314,6 +317,9 @@ int Difftest::step() {
         if (do_instr_commit(i)) {
           return 1;
         }
+        if (do_store_check()) {
+          return 1;
+        }
         dut->commit[i].valid = 0;
         num_commit += 1 + dut->commit[i].nFused;
       }
@@ -611,13 +617,13 @@ void Difftest::do_first_instr_commit() {
 
 int Difftest::do_store_check() {
 #ifdef CONFIG_DIFFTEST_STOREEVENT
-  for (int i = 0; i < CONFIG_DIFF_STORE_WIDTH; i++) {
-    if (!dut->store[i].valid) {
-      return 0;
-    }
-    auto addr = dut->store[i].addr;
-    auto data = dut->store[i].data;
-    auto mask = dut->store[i].mask;
+  while (!store_event_queue.empty()) {
+    auto store_event = store_event_queue.front();
+
+    auto addr = store_event.addr;
+    auto data = store_event.data;
+    auto mask = store_event.mask;
+
     if (proxy->store_commit(&addr, &data, &mask)) {
 #ifdef FUZZING
       if (in_disambiguation_state()) {
@@ -626,13 +632,15 @@ int Difftest::do_store_check() {
       }
 #endif
       display();
-      printf("Mismatch for store commits %d: \n", i);
+      printf("Mismatch for store commits \n");
       printf("  REF commits addr 0x%lx, data 0x%lx, mask 0x%x\n", addr, data, mask);
-      printf("  DUT commits addr 0x%lx, data 0x%lx, mask 0x%x\n", dut->store[i].addr, dut->store[i].data,
-             dut->store[i].mask);
+      printf("  DUT commits addr 0x%lx, data 0x%lx, mask 0x%x\n", store_event.addr, store_event.data, store_event.mask);
+
+      store_event_queue.pop();
       return 1;
     }
-    dut->store[i].valid = 0;
+
+    store_event_queue.pop();
   }
 #endif // CONFIG_DIFFTEST_STOREEVENT
   return 0;
@@ -1044,6 +1052,19 @@ int Difftest::do_golden_memory_update() {
 }
 #endif
 
+#ifdef CONFIG_DIFFTEST_STOREEVENT
+void Difftest::store_event_record() {
+  for (int i = 0; i < CONFIG_DIFF_STORE_WIDTH; i++) {
+    if (dut->store[i].valid) {
+      store_event_t event{dut->store[i].addr, dut->store[i].data, dut->store[i].mask};
+      store_event_queue.push(event);
+
+      dut->store[i].valid = 0;
+    }
+  }
+}
+#endif
+
 int Difftest::check_timeout() {
   // check whether there're any commits since the simulation starts
   if (!has_commit && ticks > last_commit + firstCommit_limit) {

src/test/csrc/difftest/difftest.h

@@ -21,6 +21,7 @@
 #include "difftrace.h"
 #include "golden.h"
 #include "refproxy.h"
+#include <queue>
 #include <vector>
 #ifdef FUZZING
 #include "emu.h"
@@ -62,6 +63,13 @@ enum retire_mem_type {
   RET_STORE
 };
 
+class store_event_t {
+public:
+  uint64_t addr;
+  uint64_t data;
+  uint8_t mask;
+};
+
 class CommitTrace {
 public:
   uint64_t pc;
@@ -302,6 +310,10 @@ class Difftest {
   uint64_t track_instr = 0;
 #endif
 
+#ifdef CONFIG_DIFFTEST_STOREEVENT
+  std::queue<store_event_t> store_event_queue;
+  void store_event_record();
+#endif
   void update_last_commit() {
     last_commit = ticks;
   }
@@ -318,6 +330,7 @@ class Difftest {
   int do_l1tlb_check();
   int do_l2tlb_check();
   int do_golden_memory_update();
+
   inline uint64_t get_commit_data(int i) {
 #ifdef CONFIG_DIFFTEST_ARCHFPREGSTATE
     if (dut->commit[i].fpwen) {