Fixed bug #81015

Make sure that the previous opline is part of the same block,
otherwise it may be non-dominating.

The test case does not fail on PHP-7.4, but I think the general
problem can appear on 7.4 as well, so I'm applying the patch to
that branch.

NEWS

@@ -34,6 +34,8 @@ PHP                                                                        NEWS
 
 - Opcache:
   . Fixed bug #80900 (switch statement behavior inside function). (twosee)
+  . Fixed bug #81015 (Opcache optimization assumes wrong part of ternary
+    operator in if-condition). (Nikita)
 
 - XMLReader:
   . Fixed bug #73246 (XMLReader: encoding length not checked). (cmb)

ext/opcache/Optimizer/zend_ssa.c

@@ -255,6 +255,14 @@ static void place_essa_pis(
 			default:
 				continue;
 		}
+
+		/* The following patterns all inspect the opline directly before the JMPZ opcode.
+		 * Make sure that it is part of the same block, otherwise it might not be a dominating
+		 * assignment. */
+		if (blocks[j].len == 1) {
+			continue;
+		}
+
 		if (opline->op1_type == IS_TMP_VAR &&
 		    ((opline-1)->opcode == ZEND_IS_EQUAL ||
 		     (opline-1)->opcode == ZEND_IS_NOT_EQUAL ||

ext/opcache/tests/bug81015.phpt

@@ -0,0 +1,26 @@
+--TEST--
+Bug #81015: Opcache optimization assumes wrong part of ternary operator in if-condition
+--FILE--
+<?php
+
+function ternary(bool $enabled, ?string $value): void
+{
+	// the "true" part is not as trivial in the real case
+	if ($enabled ? true : $value === null) {
+		echo ($value ?? 'NULL') . "\n";
+	} else {
+		echo "INVALID\n";
+	}
+}
+
+ternary(true, 'value');
+ternary(true, null);
+ternary(false, 'value');
+ternary(false, null);
+
+?>
+--EXPECT--
+value
+NULL
+INVALID
+NULL