Cache string value locally

jkeiser · jkeiser · commit 57eb55446f3a · 2020-08-18T21:25:03.000-07:00
diff --git a/src/generic/stage2/json_iterator.h b/src/generic/stage2/json_iterator.h
@@ -10,7 +10,6 @@ class json_iterator {
   uint32_t *next_structural;
   dom_parser_implementation &dom_parser;
   uint32_t depth{0};
-  const uint8_t *value{}; // Used to keep a value around between states
 
   template<bool STREAMING, typename T>
   SIMDJSON_WARN_UNUSED simdjson_really_inline error_code walk_document(T &visitor) noexcept;
@@ -26,9 +25,8 @@ class json_iterator {
   simdjson_really_inline char peek_next_char() {
     return buf[*(next_structural)];
   }
-  simdjson_really_inline char advance() {
-    value = &buf[*(next_structural++)];
-    return *value;
+  simdjson_really_inline const uint8_t *advance() {
+    return &buf[*(next_structural++)];
   }
   simdjson_really_inline size_t remaining_len() {
     return dom_parser.len - *(next_structural-1);
@@ -97,30 +95,32 @@ SIMDJSON_WARN_UNUSED simdjson_really_inline error_code json_iterator::walk_docum
   //
   // Read first value
   //
-  advance();
+  {
+    auto value = advance();
+
+    // Make sure the outer hash or array is closed before continuing; otherwise, there are ways we
+    // could get into memory corruption. See https://github.com/simdjson/simdjson/issues/906
+    if (!STREAMING) {
+      switch (*value) {
+        case '{':
+          if (last_structural() != '}') {
+            return TAPE_ERROR;
+          }
+          break;
+        case '[':
+          if (last_structural() != ']') {
+            return TAPE_ERROR;
+          }
+          break;
+      }
+    }
 
-  // Make sure the outer hash or array is closed before continuing; otherwise, there are ways we
-  // could get into memory corruption. See https://github.com/simdjson/simdjson/issues/906
-  if (!STREAMING) {
     switch (*value) {
-      case '{':
-        if (last_structural() != '}') {
-          return TAPE_ERROR;
-        }
-        break;
-      case '[':
-        if (last_structural() != ']') {
-          return TAPE_ERROR;
-        }
-        break;
+      case '{': if (!empty_object(visitor)) { goto object_begin; }; break;
+      case '[': if (!empty_array(visitor)) { goto array_begin; }; break;
+      default: SIMDJSON_TRY( visitor.root_primitive(*this, value) ); break;
     }
   }
-
-  switch (*value) {
-    case '{': if (!empty_object(visitor)) { goto object_begin; }; break;
-    case '[': if (!empty_array(visitor)) { goto array_begin; }; break;
-    default: SIMDJSON_TRY( visitor.root_primitive(*this, value) ); break;
-  }
   goto document_end;
 
 //
@@ -131,24 +131,33 @@ SIMDJSON_WARN_UNUSED simdjson_really_inline error_code json_iterator::walk_docum
   if (depth >= dom_parser.max_depth()) { log_error("Exceeded max depth!"); return DEPTH_ERROR; }
   SIMDJSON_TRY( visitor.start_object(*this) );
 
-  if (advance() != '"') { log_error("Object does not start with a key"); return TAPE_ERROR; }
-  visitor.increment_count(*this);
-  SIMDJSON_TRY( visitor.key(*this, value) );
+  {
+    auto key = advance();
+    if (*key != '"') { log_error("Object does not start with a key"); return TAPE_ERROR; }
+    visitor.increment_count(*this);
+    SIMDJSON_TRY( visitor.key(*this, key) );
+  }
 
 object_field:
-  if (simdjson_unlikely( advance() != ':' )) { log_error("Missing colon after key in object"); return TAPE_ERROR; }
-  switch (advance()) {
-    case '{': if (!empty_object(visitor)) { goto object_begin; }; break;
-    case '[': if (!empty_array(visitor)) { goto array_begin; }; break;
-    default: SIMDJSON_TRY( visitor.primitive(*this, value) ); break;
+  if (simdjson_unlikely( *advance() != ':' )) { log_error("Missing colon after key in object"); return TAPE_ERROR; }
+  {
+    auto value = advance();
+    switch (*value) {
+      case '{': if (!empty_object(visitor)) { goto object_begin; }; break;
+      case '[': if (!empty_array(visitor)) { goto array_begin; }; break;
+      default: SIMDJSON_TRY( visitor.primitive(*this, value) ); break;
+    }
   }
 
 object_continue:
-  switch (advance()) {
+  switch (*advance()) {
     case ',':
       visitor.increment_count(*this);
-      if (simdjson_unlikely( advance() != '"' )) { log_error("Key string missing at beginning of field in object"); return TAPE_ERROR; }
-      SIMDJSON_TRY( visitor.key(*this, value) );
+      {
+        auto key = advance();
+        if (simdjson_unlikely( *key != '"' )) { log_error("Key string missing at beginning of field in object"); return TAPE_ERROR; }
+        SIMDJSON_TRY( visitor.key(*this, key) );
+      }
       goto object_field;
     case '}': SIMDJSON_TRY( visitor.end_object(*this) ); goto scope_end;
     default: log_error("No comma between object fields"); return TAPE_ERROR;
@@ -170,14 +179,17 @@ SIMDJSON_WARN_UNUSED simdjson_really_inline error_code json_iterator::walk_docum
   visitor.increment_count(*this);
 
 array_value:
-  switch (advance()) {
-    case '{': if (!empty_object(visitor)) { goto object_begin; }; break;
-    case '[': if (!empty_array(visitor)) { goto array_begin; }; break;
-    default: SIMDJSON_TRY( visitor.primitive(*this, value) ); break;
+  {
+    auto value = advance();
+    switch (*value) {
+      case '{': if (!empty_object(visitor)) { goto object_begin; }; break;
+      case '[': if (!empty_array(visitor)) { goto array_begin; }; break;
+      default: SIMDJSON_TRY( visitor.primitive(*this, value) ); break;
+    }
   }
 
 array_continue:
-  switch (advance()) {
+  switch (*advance()) {
     case ',': visitor.increment_count(*this); goto array_value;
     case ']': SIMDJSON_TRY( visitor.end_array(*this) ); goto scope_end;
     default: log_error("Missing comma between array values"); return TAPE_ERROR;
