IC: introduce empty

Author: undingen

src/asm_writing/icinfo.cpp

@@ -76,6 +76,7 @@ void ICInvalidator::invalidateAll() {
 void ICSlotInfo::clear() {
     ic->clear(this);
     decref_infos.clear();
+    empty = true;
 }
 
 ICSlotRewrite::ICSlotRewrite(ICInfo* ic, const char* debug_name)
@@ -175,6 +176,7 @@ void ICSlotRewrite::commit(CommitHook* hook, std::vector<void*> gc_references,
     }
 
     llvm::sys::Memory::InvalidateInstructionCache(slot_start, ic->getSlotSize());
+    ic_entry->empty = false;
 }
 
 void ICSlotRewrite::addDependenceOn(ICInvalidator& invalidator) {
@@ -209,7 +211,24 @@ std::unique_ptr<ICSlotRewrite> ICInfo::startRewrite(const char* debug_name) {
 }
 
 ICSlotInfo* ICInfo::pickEntryForRewrite(const char* debug_name) {
-    int num_slots = getNumSlots();
+    int num_slots = slots.size();
+
+    for (int _i = 0; _i < num_slots; _i++) {
+        int i = (_i + next_slot_to_try) % num_slots;
+
+        ICSlotInfo& sinfo = slots[i];
+        assert(sinfo.num_inside >= 0);
+        if (sinfo.num_inside || !sinfo.empty)
+            continue;
+
+        if (VERBOSITY() >= 4) {
+            printf("picking %s icentry to in-use slot %d at %p\n", debug_name, i, start_addr);
+        }
+
+        next_slot_to_try = i;
+        return &sinfo;
+    }
+
     for (int _i = 0; _i < num_slots; _i++) {
         int i = (_i + next_slot_to_try) % num_slots;
 
@@ -371,6 +390,15 @@ void ICInfo::clear(ICSlotInfo* icentry) {
 
     // writer->endWithSlowpath();
     llvm::sys::Memory::InvalidateInstructionCache(start, getSlotSize());
+
+    for (int i = 0; i < slots.size(); ++i) {
+        if (&slots[i] == icentry) {
+            next_slot_to_try = i;
+            break;
+        }
+    }
+
+    icentry->empty = true;
 }
 
 bool ICInfo::shouldAttempt() {

src/asm_writing/icinfo.h

@@ -60,6 +60,7 @@ struct ICSlotInfo {
     ICInfo* ic;
     int idx;        // the index inside the ic
     int num_inside; // the number of stack frames that are currently inside this slot
+    bool empty = true;
 
     std::vector<void*> gc_references;
     std::vector<DecrefInfo> decref_infos;