Fix GH-11245 (In some specific cases SWITCH with one default statement will cause segfault)

Zend/Optimizer/block_pass.c

@@ -257,6 +257,10 @@ static void zend_optimize_block(zend_basic_block *block, zend_op_array *op_array
 				break;
 
 			case ZEND_FREE:
+				/* Note: Only remove the source if the source is local to this block.
+				 * If it's not local, then the other blocks successors must also eventually either FREE or consume the temporary,
+				 * hence removing the temporary is not safe in the general case, especially when other consumers are not FREE.
+				 * A FREE may not be removed without also removing the source's result, because otherwise that would cause a memory leak. */
 				if (opline->op1_type == IS_TMP_VAR) {
 					src = VAR_SOURCE(opline->op1);
 					if (src) {
@@ -265,6 +269,7 @@ static void zend_optimize_block(zend_basic_block *block, zend_op_array *op_array
 							case ZEND_BOOL_NOT:
 								/* T = BOOL(X), FREE(T) => T = BOOL(X) */
 								/* The remaining BOOL is removed by a separate optimization */
+								/* The source is a bool, no source removals take place, so this may be done non-locally. */
 								VAR_SOURCE(opline->op1) = NULL;
 								MAKE_NOP(opline);
 								++(*opt_count);
@@ -283,6 +288,9 @@ static void zend_optimize_block(zend_basic_block *block, zend_op_array *op_array
 							case ZEND_PRE_DEC_OBJ:
 							case ZEND_PRE_INC_STATIC_PROP:
 							case ZEND_PRE_DEC_STATIC_PROP:
+								if (src < op_array->opcodes + block->start) {
+									break;
+								}
 								src->result_type = IS_UNUSED;
 								VAR_SOURCE(opline->op1) = NULL;
 								MAKE_NOP(opline);
@@ -295,7 +303,7 @@ static void zend_optimize_block(zend_basic_block *block, zend_op_array *op_array
 				} else if (opline->op1_type == IS_VAR) {
 					src = VAR_SOURCE(opline->op1);
 					/* V = OP, FREE(V) => OP. NOP */
-					if (src &&
+					if (src >= op_array->opcodes + block->start &&
 					    src->opcode != ZEND_FETCH_R &&
 					    src->opcode != ZEND_FETCH_STATIC_PROP_R &&
 					    src->opcode != ZEND_FETCH_DIM_R &&

ext/opcache/tests/opt/gh11245_1.phpt

@@ -0,0 +1,33 @@
+--TEST--
+GH-11245: In some specific cases SWITCH with one default statement will cause segfault (VAR variation)
+--INI--
+opcache.enable=1
+opcache.enable_cli=1
+opcache.optimization_level=0x7FFFBFFF
+opcache.opt_debug_level=0x20000
+opcache.preload=
+--EXTENSIONS--
+opcache
+--FILE--
+<?php
+function xx() { return "somegarbage"; }
+switch (xx()) {
+	default:
+		if (!empty($xx)) {return;}
+}
+?>
+--EXPECTF--
+$_main:
+     ; (lines=4, args=0, vars=1, tmps=1)
+     ; (after optimizer)
+     ; %s
+0000 T1 = ISSET_ISEMPTY_CV (empty) CV0($xx)
+0001 JMPNZ T1 0003
+0002 RETURN null
+0003 RETURN int(1)
+
+xx:
+     ; (lines=1, args=0, vars=0, tmps=0)
+     ; (after optimizer)
+     ; %s
+0000 RETURN string("somegarbage")

ext/opcache/tests/opt/gh11245_2.phpt

@@ -0,0 +1,35 @@
+--TEST--
+GH-11245: In some specific cases SWITCH with one default statement will cause segfault (TMP variation)
+--INI--
+opcache.enable=1
+opcache.enable_cli=1
+opcache.optimization_level=0x7FFFBFFF
+opcache.opt_debug_level=0x20000
+opcache.preload=
+--EXTENSIONS--
+opcache
+--FILE--
+<?php
+class X {
+    // Chosen to test for a memory leak.
+    static $prop = "aa";
+}
+switch (++X::$prop) {
+    default:
+        if (empty($xx)) {return;}
+}
+?>
+--EXPECTF--
+$_main:
+     ; (lines=7, args=0, vars=1, tmps=2)
+     ; (after optimizer)
+     ; %s
+0000 T1 = PRE_INC_STATIC_PROP string("prop") string("X")
+0001 T2 = ISSET_ISEMPTY_CV (empty) CV0($xx)
+0002 JMPZ T2 0005
+0003 FREE T1
+0004 RETURN null
+0005 FREE T1
+0006 RETURN int(1)
+LIVE RANGES:
+     1: 0001 - 0005 (tmp/var)