Don't replace values in unreachable code in sccp

While technically legal, this may cause unexpected situations
(in this example, setting an FE_FREE operand to constant null)
and is suboptimal anyway. It's better to preserve the vacuous type
and drop it later (though we currently don't implement this).

Author: nikic

ext/opcache/Optimizer/sccp.c

@@ -2139,6 +2139,12 @@ static zval *value_from_type_and_range(sccp_ctx *ctx, int var_num, zval *tmp) {
 		return NULL;
 	}
 
+	if (!(info->type & MAY_BE_ANY)) {
+		/* This code must be unreachable. We could replace operands with NULL, but this doesn't
+		 * really make things better. It would be better to later remove this code entirely. */
+		return NULL;
+	}
+
 	if (!(info->type & ((MAY_BE_ANY|MAY_BE_UNDEF)-MAY_BE_NULL))) {
 		ZVAL_NULL(tmp);
 		return tmp;

ext/opcache/tests/opt/sccp_022.phpt

@@ -17,18 +17,23 @@ function foo(int $x) {
     $a->foo = 5;
     echo $a[1];
 }
+function bar() {
+    foreach ($a as $v) {
+        foreach ($v as $v2) {}
+    }
+}
 ?>
 --EXPECTF--
 $_main:
      ; (lines=1, args=0, vars=0, tmps=0)
      ; (after optimizer)
-     ; %ssccp_022.php:1-10
+     ; %s
 0000 RETURN int(1)
 
 foo:
-     ; (lines=10, args=1, vars=2, tmps=1)
+     ; (lines=11, args=1, vars=2, tmps=1)
      ; (after optimizer)
-     ; %ssccp_022.php:2-8
+     ; %s
 0000 CV0($x) = RECV 1
 0001 ASSIGN_DIM CV1($a) int(0)
 0002 OP_DATA CV0($x)
@@ -37,5 +42,23 @@ foo:
 0005 ECHO string("5")
 0006 ASSIGN_OBJ CV1($a) string("foo")
 0007 OP_DATA int(5)
-0008 T2 = FETCH_DIM_R null int(1)
-0009 RETURN null
+0008 T2 = FETCH_DIM_R CV1($a) int(1)
+0009 ECHO T2
+0010 RETURN null
+
+bar:
+     ; (lines=9, args=0, vars=3, tmps=2)
+     ; (after optimizer)
+     ; %s
+0000 V3 = FE_RESET_R CV0($a) 0007
+0001 FE_FETCH_R V3 CV1($v) 0007
+0002 V4 = FE_RESET_R CV1($v) 0005
+0003 FE_FETCH_R V4 CV2($v2) 0005
+0004 JMP 0003
+0005 FE_FREE V4
+0006 JMP 0001
+0007 FE_FREE V3
+0008 RETURN null
+LIVE RANGES:
+     3: 0001 - 0007 (loop)
+     4: 0003 - 0005 (loop)