Fix removal of unreachable code in SCCP

Due to a wrongly placed check, we were only performing the
unreachable code removal if there were loop vars...

ext/opcache/Optimizer/scdf.c

@@ -189,6 +189,9 @@ static zend_bool kept_alive_by_loop_var_free(scdf_ctx *scdf, uint32_t block_idx)
 	const zend_op_array *op_array = scdf->op_array;
 	const zend_cfg *cfg = &scdf->ssa->cfg;
 	const zend_basic_block *block = &cfg->blocks[block_idx];
+	if (!(cfg->flags & ZEND_FUNC_FREE_LOOP_VAR)) {
+		return 0;
+	}
 	for (i = block->start; i < block->start + block->len; i++) {
 		zend_op *opline = &op_array->opcodes[i];
 		if (opline->opcode == ZEND_FE_FREE ||
@@ -215,10 +218,6 @@ int scdf_remove_unreachable_blocks(scdf_ctx *scdf) {
 	zend_ssa *ssa = scdf->ssa;
 	int i;
 	int removed_ops = 0;
-
-	if (!(ssa->cfg.flags & ZEND_FUNC_FREE_LOOP_VAR)) {
-		return 0;
-	}
 	for (i = 0; i < ssa->cfg.blocks_count; i++) {
 		if (!zend_bitset_in(scdf->executable_blocks, i)
 				&& (ssa->cfg.blocks[i].flags & ZEND_BB_REACHABLE)

ext/opcache/tests/opt/sccp_026.phpt

@@ -0,0 +1,38 @@
+--TEST--
+SCCP 026: Elimination of dead code due to conflicting type checks
+--INI--
+opcache.enable=1
+opcache.enable_cli=1
+opcache.optimization_level=-1
+opcache.opt_debug_level=0x20000
+opcache.preload=
+--SKIPIF--
+<?php require_once('skipif.inc'); ?>
+--FILE--
+<?php
+function test($var) {
+    if (!is_string($var) || (is_object($var) && !method_exists($var, '__toString'))) {
+        return;
+    }
+
+    var_dump($username); 
+}
+?>
+--EXPECTF--
+$_main: ; (lines=1, args=0, vars=0, tmps=0)
+    ; (after optimizer)
+    ; %s:1-10
+L0 (10):    RETURN int(1)
+
+test: ; (lines=9, args=1, vars=2, tmps=1)
+    ; (after optimizer)
+    ; %s:2-8
+L0 (2):     CV0($var) = RECV 1
+L1 (3):     T2 = TYPE_CHECK (string) CV0($var)
+L2 (3):     JMPZ T2 L4
+L3 (3):     JMP L5
+L4 (4):     RETURN null
+L5 (7):     INIT_FCALL 1 %d string("var_dump")
+L6 (7):     SEND_VAR CV1($username) 1
+L7 (7):     DO_ICALL
+L8 (8):     RETURN null