use a binary search to find/insert CompiledFunction*'s into the registry

src/codegen/unwinding.cpp

@@ -88,19 +88,55 @@ void parseEhFrame(uint64_t start_addr, uint64_t size, uint64_t* out_data, uint64
 
 class CFRegistry {
 private:
-    // TODO use a binary search tree
     std::vector<CompiledFunction*> cfs;
 
-public:
-    void registerCF(CompiledFunction* cf) { cfs.push_back(cf); }
-
+    // similar to Java's Array.binarySearch:
+    // return values are either:
+    //   >= 0 : the index where a given item was found
+    //   < 0  : a negative number that can be transformed (using "-num-1") into the insertion point
+    //
     // addr is the return address of the callsite, so we will check it against
     // the region (start, end] (opposite-endedness of normal half-open regions)
-    CompiledFunction* getCFForAddress(uint64_t addr) {
-        for (auto* cf : cfs) {
-            if (cf->code_start < addr && addr <= cf->code_start + cf->code_size)
-                return cf;
+    //
+    int find_cf(uint64_t addr) {
+        int l = 0;
+        int r = cfs.size() - 1;
+        while (l <= r) {
+            int mid = l + (r - l) / 2;
+            auto mid_cf = cfs[mid];
+            if (addr <= mid_cf->code_start) {
+                r = mid - 1;
+            } else if (addr > mid_cf->code_start + mid_cf->code_size) {
+                l = mid + 1;
+            } else {
+                return mid;
+            }
+        }
+        return -(l + 1);
+    }
+
+public:
+    void registerCF(CompiledFunction* cf) {
+        if (cfs.empty()) {
+            cfs.push_back(cf);
+            return;
         }
+
+        int idx = find_cf((uint64_t)cf->code_start);
+        if (idx >= 0)
+            RELEASE_ASSERT(0, "CompiledFunction registered twice?");
+
+        cfs.insert(cfs.begin() + (-idx - 1), cf);
+    }
+
+    CompiledFunction* getCFForAddress(uint64_t addr) {
+        if (cfs.empty())
+            return NULL;
+
+        int idx = find_cf(addr);
+        if (idx >= 0)
+            return cfs[idx];
+
         return NULL;
     }
 };