Merge branch 'PHP-8.0'

* PHP-8.0:
  Fix DCE of FREE of COALESCE

Note that this is a non-trivial merge, as opt/coalesce.phpt
regresses with this change. I'll have to see if it can be
improved.

Author: nikic

Zend/Optimizer/dce.c

@@ -527,6 +527,16 @@ int dce_optimize_op_array(zend_op_array *op_array, zend_ssa *ssa, bool reorder_d
 	ctx.phi_dead = alloca(sizeof(zend_ulong) * ctx.phi_worklist_len);
 	memset(ctx.phi_dead, 0xff, sizeof(zend_ulong) * ctx.phi_worklist_len);
 
+	/* Mark non-CV phis as live. Even if the result is unused, we generally cannot remove one
+	 * of the producing instructions, as it combines producing the result with control flow.
+	 * This can be made more precise if there are any cases where this is not the case. */
+	FOREACH_PHI(phi) {
+		if (phi->var >= op_array->last_var) {
+			zend_bitset_excl(ctx.phi_dead, phi->ssa_var);
+			add_phi_sources_to_worklists(&ctx, phi, 0);
+		}
+	} FOREACH_PHI_END();
+
 	/* Mark reacable instruction without side effects as dead */
 	int b = ssa->cfg.blocks_count;
 	while (b > 0) {

ext/opcache/tests/opt/coalesce.phpt

@@ -29,15 +29,17 @@ $_main:
 0000 RETURN int(1)
 
 a:
-     ; (lines=2, args=0, vars=1, tmps=1)
+     ; (lines=3, args=0, vars=1, tmps=1)
      ; (after optimizer)
      ; %s
-0000 T1 = COALESCE CV0($test) 0001
-0001 RETURN bool(true)
+0000 T1 = COALESCE CV0($test) 0002
+0001 T1 = QM_ASSIGN bool(true)
+0002 RETURN bool(true)
 
 b:
-     ; (lines=2, args=0, vars=1, tmps=1)
+     ; (lines=3, args=0, vars=1, tmps=1)
      ; (after optimizer)
      ; %s
-0000 T1 = COALESCE CV0($test) 0001
-0001 RETURN bool(true)
+0000 T1 = COALESCE CV0($test) 0002
+0001 T1 = ASSIGN CV0($test) bool(true)
+0002 RETURN bool(true)

ext/opcache/tests/opt/dce_010.phpt

@@ -0,0 +1,17 @@
+--TEST--
+Incorrect DCE of FREE of COALESCE
+--FILE--
+<?php
+
+function test(?string $str) {
+    $str ?? $str = '';
+    return strlen($str);
+}
+
+$foo = 'foo';
+$foo .= 'bar';
+var_dump(test($foo));
+
+?>
+--EXPECT--
+int(6)