Fix GH-12953: SSA integrity verification failed when loading composer classmaps with more than 11k elements

This is a false positive. The cycle detection code stops at 10.000
iterations. Instead of stopping at a fixed amount, make it more robust
by implementing Floyd's cycle detection algorithm.

Closes GH-12954.

Author: nielsdos

Diff for: NEWS

@@ -2,6 +2,10 @@ PHP                                                                        NEWS
 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 ?? ??? ????, PHP 8.2.15
 
+- Core:
+  . Fixed bug GH-12953 (false positive SSA integrity verification failed when
+    loading composer classmaps with more than 11k elements). (nielsdos)
+
 - Cli:
   . Fix incorrect timeout in built-in web server when using router script and
     max_input_time. (ilutov)

Diff for: Zend/Optimizer/ssa_integrity.c

@@ -122,7 +122,7 @@ void ssa_verify_integrity(zend_op_array *op_array, zend_ssa *ssa, const char *ex
 	/* Vars */
 	for (i = 0; i < ssa->vars_count; i++) {
 		zend_ssa_var *var = &ssa->vars[i];
-		int use, c;
+		int use;
 		uint32_t type = ssa->var_info[i].type;
 
 		if (var->definition < 0 && !var->definition_phi && i > op_array->last_var) {
@@ -148,23 +148,45 @@ void ssa_verify_integrity(zend_op_array *op_array, zend_ssa *ssa, const char *ex
 			}
 		}
 
-		c = 0;
-		FOREACH_USE(var, use) {
-			if (++c > 10000) {
+		/* Floyd's cycle detection algorithm, applied for use chain. */
+		use = var->use_chain;
+		int second_use = use;
+		while (use >= 0 && second_use >= 0) {
+			use = zend_ssa_next_use(ssa->ops, var - ssa->vars, use);
+			second_use = zend_ssa_next_use(ssa->ops, var - ssa->vars, second_use);
+			if (second_use < 0) {
+				break;
+			}
+			second_use = zend_ssa_next_use(ssa->ops, var - ssa->vars, second_use);
+			if (use == second_use) {
 				FAIL("cycle in uses of " VARFMT "\n", VAR(i));
 				goto finish;
 			}
+		}
+
+		FOREACH_USE(var, use) {
 			if (!is_used_by_op(ssa, use, i)) {
 				fprintf(stderr, "var " VARFMT " not in uses of op %d\n", VAR(i), use);
 			}
 		} FOREACH_USE_END();
 
-		c = 0;
-		FOREACH_PHI_USE(var, phi) {
-			if (++c > 10000) {
+		/* Floyd's cycle detection algorithm, applied for phi nodes. */
+		phi = var->phi_use_chain;
+		zend_ssa_phi *second_phi = phi;
+		while (phi && second_phi) {
+			phi = zend_ssa_next_use_phi(ssa, var - ssa->vars, phi);
+			second_phi = zend_ssa_next_use_phi(ssa, var - ssa->vars, second_phi);
+			if (!second_phi) {
+				break;
+			}
+			second_phi = zend_ssa_next_use_phi(ssa, var - ssa->vars, second_phi);
+			if (phi == second_phi) {
 				FAIL("cycle in phi uses of " VARFMT "\n", VAR(i));
 				goto finish;
 			}
+		}
+
+		FOREACH_PHI_USE(var, phi) {
 			if (!is_in_phi_sources(ssa, phi, i)) {
 				FAIL("var " VARFMT " not in phi sources of %d\n", VAR(i), phi->ssa_var);
 			}