From: Dmitry Stogov <dmitry@zend.com>
Date: Wed, 9 Dec 2015 19:22:07 +0000 (+0300)
Subject: Explain the disabled optimization pattern
X-Git-Tag: php-7.1.0alpha1~689
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=7fd7734e5872872e7e739bce3e074f463927ba25;p=php

Explain the disabled optimization pattern
---

diff --git a/ext/opcache/Optimizer/pass2.c b/ext/opcache/Optimizer/pass2.c
index 3573c1038c..b61d799fad 100644
--- a/ext/opcache/Optimizer/pass2.c
+++ b/ext/opcache/Optimizer/pass2.c
@@ -114,14 +114,21 @@ void zend_optimizer_pass2(zend_op_array *op_array)
 			case ZEND_JMPZ_EX:
 			case ZEND_JMPNZ_EX:
 				/* convert Ti = JMPZ_EX(Ti, L) to JMPZ(Ti, L) */
-				if (0 && /* FIXME: temporary disable unsafe pattern */
-				    ZEND_OP1_TYPE(opline) == IS_TMP_VAR &&
+#if 0
+				/* Disabled unsafe pattern: in conjunction with
+				 * ZEND_VM_SMART_BRANCH() this may improperly eliminate
+				 * assignment to Ti.
+				 */
+				if (ZEND_OP1_TYPE(opline) == IS_TMP_VAR &&
 				    ZEND_RESULT_TYPE(opline) == IS_TMP_VAR &&
 				    ZEND_OP1(opline).var == ZEND_RESULT(opline).var) {
 					opline->opcode -= 3;
+					SET_UNUSED(opline->result);
+				} else
+#endif
 				/* convert Ti = JMPZ_EX(C, L) => Ti = QM_ASSIGN(C)
 				   in case we know it wouldn't jump */
-				} else if (ZEND_OP1_TYPE(opline) == IS_CONST) {
+				if (ZEND_OP1_TYPE(opline) == IS_CONST) {
 					int should_jmp = zend_is_true(&ZEND_OP1_LITERAL(opline));
 					if (opline->opcode == ZEND_JMPZ_EX) {
 						should_jmp = !should_jmp;