Fix DCE with FE_FETCH

For now, don't treat FE_FETCH op2 as no-val use. See GH-4982.

Author: nikic

ext/opcache/Optimizer/zend_ssa.h

@@ -217,9 +217,10 @@ static zend_always_inline zend_bool zend_ssa_is_no_val_use(const zend_op *opline
 	if (opline->opcode == ZEND_ASSIGN || opline->opcode == ZEND_UNSET_CV) {
 		return ssa_op->op1_use == var && ssa_op->op2_use != var;
 	}
-	if (opline->opcode == ZEND_FE_FETCH_R) {
+	// TODO: Reenable this after changing the SSA structure.
+	/*if (opline->opcode == ZEND_FE_FETCH_R) {
 		return ssa_op->op2_use == var && ssa_op->op1_use != var;
-	}
+	}*/
 	if (ssa_op->result_use == var && opline->opcode != ZEND_ADD_ARRAY_ELEMENT) {
 		return ssa_op->op1_use != var && ssa_op->op2_use != var;
 	}

ext/opcache/tests/fe_fetch_dce.phpt

@@ -0,0 +1,22 @@
+--TEST--
+Incorrect DCE with FE_FETCH
+--INI--
+opcache.enable=1
+opcache.enable_cli=1
+opcache.optimization_level=-1
+--FILE--
+<?php
+
+function test() {
+    $a = ["3"];
+    $x = 1;
+    foreach ($a as $x) {
+        $x = 2.0;
+    }
+    var_dump($x);
+}
+test();
+
+?>
+--EXPECT--
+float(2)