Run autoloader only once for unqualified functions in a namespace

We bind the namespaced function to the global one if such a function exists.

Zend/tests/autoloading/function/exceptions_during_autoloading004.phpt

@@ -29,7 +29,6 @@ namespace bar {
     try {
         foo();
     } catch (\Throwable $e) {
-        /* No autoloading for unqualified function names */
         do {
             echo $e::class, ': ', $e->getMessage(), "\n";
         } while ($e = $e->getPrevious());
@@ -52,7 +51,8 @@ Try-catch around function_exists()
 autoload_first
 first
 Try-catch around unqualified function call
-Error: Call to undefined function bar\foo()
+autoload_first
+Exception: first
 Try-catch around qualified function call
 autoload_first
 Exception: first

Zend/tests/autoloading/function/global_fallback002.phpt

@@ -1,5 +1,5 @@
 --TEST--
-Fallback to global function should not trigger autoloading.
+Fallback to global function triggers autoloading once.
 --FILE--
 <?php
 
@@ -21,4 +21,5 @@ namespace bar {
 
 ?>
 --EXPECT--
+function loader called with bar\foo
 I am foo in global namespace.

Zend/tests/autoloading/function/global_fallback003.phpt

@@ -0,0 +1,27 @@
+--TEST--
+Fallback to non-existent function triggers autoloading once in namespace, once in global.
+--FILE--
+<?php
+
+namespace {
+    function loader($name) {
+        echo "function loader called with $name\n";
+    }
+
+    autoload_register_function('loader');
+}
+
+namespace bar {
+    try {
+        non_existent_function();
+    }
+    catch (\Error $e) {
+        echo "Error correctly caught: " . $e->getMessage() . "\n";
+    }
+}
+
+?>
+--EXPECT--
+function loader called with bar\non_existent_function
+function loader called with non_existent_function
+Error correctly caught: Call to undefined function bar\non_existent_function()

Zend/tests/autoloading/function/global_fallback_doesnt_repeat_autoloading.phpt

@@ -0,0 +1,42 @@
+--TEST--
+Fallback to global function should trigger autoloading only once per namespace.
+--FILE--
+<?php
+
+namespace {
+    function loader($name) {
+        echo "function loader called with $name\n";
+    }
+
+    autoload_register_function('loader');
+
+    function foo() {
+        echo "I am foo in global namespace.\n";
+    }
+}
+
+namespace bar {
+    foo();
+
+    for ($i = 0; $i < 3; $i += 1) {
+        foo();
+    }
+}
+namespace bar {
+    foo();
+}
+
+namespace Quux {
+    foo();
+}
+
+?>
+--EXPECT--
+function loader called with bar\foo
+I am foo in global namespace.
+I am foo in global namespace.
+I am foo in global namespace.
+I am foo in global namespace.
+I am foo in global namespace.
+function loader called with Quux\foo
+I am foo in global namespace.

Zend/zend_vm_def.h

@@ -3859,19 +3859,27 @@ ZEND_VM_HOT_HANDLER(69, ZEND_INIT_NS_FCALL_BY_NAME, ANY, CONST, NUM|CACHE_SLOT)
 	if (UNEXPECTED(fbc == NULL)) {
 		zval *function_name = (zval *)RT_CONSTANT(opline, opline->op2);
 		/* Fetch lowercase name stored in the next literal slot */
-		fbc = zend_lookup_function_ex(Z_STR_P(function_name), Z_STR_P(function_name+1), /* use_autoload */ false);
+		fbc = zend_lookup_function_ex(Z_STR_P(function_name), Z_STR_P(function_name+1), /* use_autoload */ true);
 		if (UNEXPECTED(fbc == NULL)) {
 			if (UNEXPECTED(EG(exception))) {
 				HANDLE_EXCEPTION();
 			}
 			/* Fallback onto global namespace, by fetching the unqualified lowercase name stored in the second literal slot */
-			fbc = zend_lookup_function_ex(Z_STR_P(function_name+2), Z_STR_P(function_name+2), /* use_autoload */ false);
-			if (fbc == NULL) {
+			fbc = zend_lookup_function_ex(Z_STR_P(function_name+2), Z_STR_P(function_name+2), /* use_autoload */ true);
+			if (UNEXPECTED(fbc == NULL)) {
 				if (UNEXPECTED(EG(exception))) {
 					HANDLE_EXCEPTION();
 				}
 				ZEND_VM_DISPATCH_TO_HELPER(zend_undefined_function_helper);
 			}
+			/* We bind the unqualified name to the global function
+			 * Use the lowercase name of the function stored in the first cache slot as
+			 * function names are case insensitive */
+			else {
+				zval tmp;
+				ZVAL_STR(&tmp, Z_STR_P(function_name+1));
+				do_bind_function(fbc, &tmp);
+			}
 		}
 		if (EXPECTED(fbc->type == ZEND_USER_FUNCTION) && UNEXPECTED(!RUN_TIME_CACHE(&fbc->op_array))) {
 			init_func_run_time_cache(&fbc->op_array);