Optimize goroutine switching performance.

nevkontakte · nevkontakte · commit 3067214a3127 · 2022-08-16T22:18:20.000+01:00
Avoid use of the `{...context}` syntax, which appears to have a
significant performance penalty when used in a tight loop.

In addition, apply a few further size and performance optimizations:
skip unpacking $f from the context and instead fully construct it in the
function epilogue.
diff --git a/compiler/package.go b/compiler/package.go
@@ -819,21 +819,23 @@ func translateFunction(typ *ast.FuncType, recv *ast.Ident, body *ast.BlockStmt,
 	localVarDefs := "" // Function-local var declaration at the top.
 
 	if len(c.Blocking) != 0 {
+		if funcRef == "" {
+			funcRef = "$b"
+			functionName = " $b"
+		}
+
 		localVars := append([]string{}, c.localVars...)
+		// There are several special variables involved in handling blocking functions:
 		// $r is sometimes used as a temporary variable to store blocking call result.
 		// $c indicates that a function is being resumed after a blocking call when set to true.
 		// $f is an object used to save and restore function context for blocking calls.
-		localVars = append(localVars, "$r", "$c", "$f")
+		localVars = append(localVars, "$r")
 		// If a blocking function is being resumed, initialize local variables from the saved context.
-		localVarDefs = fmt.Sprintf("var {%s} = $restore(this, {%s});\n", strings.Join(localVars, ", "), strings.Join(params, ", "))
+		localVarDefs = fmt.Sprintf("var {%s, $c} = $restore(this, {%s});\n", strings.Join(localVars, ", "), strings.Join(params, ", "))
 		// If the function gets blocked, save local variables for future.
-		saveContext := fmt.Sprintf("$f = {...$f, $r, %s};", strings.Join(c.localVars, ", "))
+		saveContext := fmt.Sprintf("var $f = {$blk: "+funcRef+", $c: true, $r, %s};", strings.Join(c.localVars, ", "))
 
-		if funcRef == "" {
-			funcRef = "$b"
-			functionName = " $b"
-		}
-		suffix = " if ($f === undefined) { $f = { $blk: " + funcRef + " }; } " + saveContext + "return $f;" + suffix
+		suffix = " " + saveContext + "return $f;" + suffix
 	} else if len(c.localVars) > 0 {
 		// Non-blocking functions simply declare local variables with no need for restore support.
 		localVarDefs = fmt.Sprintf("var %s;\n", strings.Join(c.localVars, ", "))
diff --git a/compiler/prelude/goroutines.go b/compiler/prelude/goroutines.go
@@ -225,17 +225,9 @@ var $block = function() {
 
 var $restore = function(context, params) {
   if (context !== undefined && context.$blk !== undefined) {
-    return {
-      $f: context,
-      $c: true,
-      ...context,
-    };
-  } else {
-    return {
-      $c: false,
-      ...params,
-    };
+    return context;
   }
+  return params;
 }
 
 var $send = function(chan, value) {
diff --git a/compiler/prelude/prelude_min.go b/compiler/prelude/prelude_min.go
