diff --git a/Zend/tests/bug80046.phpt b/Zend/tests/bug80046.phpt
new file mode 100644
index 00000000000..87a493c2030
--- /dev/null
+++ b/Zend/tests/bug80046.phpt
@@ -0,0 +1,22 @@
+--TEST--
+Bug #80046: FREE for SWITCH_STRING optimized away
+--FILE--
+<?php
+
+function test($foo) {
+    switch ($foo . 'Bar') {
+        case 'A':
+            throw new Exception('A');
+        default:
+            throw new Exception('Default');
+    }
+}
+try {
+    test('Foo');
+} catch (Exception $e) {
+    echo $e->getMessage(), "\n";
+}
+
+?>
+--EXPECT--
+Default
diff --git a/ext/opcache/Optimizer/block_pass.c b/ext/opcache/Optimizer/block_pass.c
index 68555115f81..7b9fb2afca7 100644
--- a/ext/opcache/Optimizer/block_pass.c
+++ b/ext/opcache/Optimizer/block_pass.c
@@ -967,7 +967,15 @@ static void assemble_code_blocks(zend_cfg *cfg, zend_op_array *op_array, zend_op
 		if (b->len == 0) {
 			continue;
 		}
-		if (b->flags & ZEND_BB_REACHABLE) {
+		if (b->flags & (ZEND_BB_REACHABLE|ZEND_BB_UNREACHABLE_FREE)) {
+			if (b->flags & ZEND_BB_UNREACHABLE_FREE) {
+				/* Only keep the FREE for the loop var */
+				ZEND_ASSERT(op_array->opcodes[b->start].opcode == ZEND_FREE
+						|| op_array->opcodes[b->start].opcode == ZEND_FE_FREE);
+				len += b->len = 1;
+				continue;
+			}
+
 			opline = op_array->opcodes + b->start + b->len - 1;
 			if (opline->opcode == ZEND_JMP) {
 				zend_basic_block *next = b + 1;
@@ -1005,7 +1013,7 @@ static void assemble_code_blocks(zend_cfg *cfg, zend_op_array *op_array, zend_op
 
 	/* Copy code of reachable blocks into a single buffer */
 	for (b = blocks; b < end; b++) {
-		if (b->flags & ZEND_BB_REACHABLE) {
+		if (b->flags & (ZEND_BB_REACHABLE|ZEND_BB_UNREACHABLE_FREE)) {
 			memcpy(opline, op_array->opcodes + b->start, b->len * sizeof(zend_op));
 			b->start = opline - new_opcodes;
 			opline += b->len;
@@ -1131,7 +1139,7 @@ static void assemble_code_blocks(zend_cfg *cfg, zend_op_array *op_array, zend_op
 	/* rebuild map (just for printing) */
 	memset(cfg->map, -1, sizeof(int) * op_array->last);
 	for (n = 0; n < cfg->blocks_count; n++) {
-		if (cfg->blocks[n].flags & ZEND_BB_REACHABLE) {
+		if (cfg->blocks[n].flags & (ZEND_BB_REACHABLE|ZEND_BB_UNREACHABLE_FREE)) {
 			cfg->map[cfg->blocks[n].start] = n;
 		}
 	}
diff --git a/ext/opcache/Optimizer/zend_cfg.c b/ext/opcache/Optimizer/zend_cfg.c
index b8088924f97..127fca5dca8 100644
--- a/ext/opcache/Optimizer/zend_cfg.c
+++ b/ext/opcache/Optimizer/zend_cfg.c
@@ -593,9 +593,8 @@ int zend_build_cfg(zend_arena **arena, const zend_op_array *op_array, uint32_t b
 	}
 
 	/* Build CFG, Step 4, Mark Reachable Basic Blocks */
-	zend_mark_reachable_blocks(op_array, cfg, 0);
-
 	cfg->flags |= flags;
+	zend_mark_reachable_blocks(op_array, cfg, 0);
 
 	return SUCCESS;
 }