More accurate "vararg" handling in DCE

Author: dstogov

ext/opcache/Optimizer/dce.c

@@ -457,14 +457,29 @@ static void try_remove_trivial_phi(context *ctx, zend_ssa_phi *phi) {
 	}
 }
 
+static inline zend_bool may_break_varargs(const zend_op_array *op_array, const zend_ssa *ssa, const zend_ssa_op *ssa_op) {
+	if (ssa_op->op1_def >= 0
+			&& ssa->vars[ssa_op->op1_def].var < op_array->num_args) {
+		return 1;
+	}
+	if (ssa_op->op2_def >= 0
+			&& ssa->vars[ssa_op->op2_def].var < op_array->num_args) {
+		return 1;
+	}
+	if (ssa_op->result_def >= 0
+			&& ssa->vars[ssa_op->result_def].var < op_array->num_args) {
+		return 1;
+	}
+	return 0;
+}
+
 int dce_optimize_op_array(zend_op_array *op_array, zend_ssa *ssa, zend_bool reorder_dtor_effects) {
 	int i;
 	zend_ssa_phi *phi;
 	int removed_ops = 0;
 
-	/* DCE of CV operations may affect vararg functions. For now simply treat all instructions
-	 * as live if varargs in use and only collect dead phis. */
-	zend_bool has_varargs = (ZEND_FUNC_INFO(op_array)->flags & ZEND_FUNC_VARARG) != 0;
+	/* DCE of CV operations that changes arguments may affect vararg functions. */
+	zend_bool has_varargs = ssa->cfg.vararg;
 
 	context ctx;
 	ctx.ssa = ssa;
@@ -504,7 +519,7 @@ int dce_optimize_op_array(zend_op_array *op_array, zend_ssa *ssa, zend_bool reor
 				add_operands_to_worklists(&ctx, &op_array->opcodes[i], &ssa->ops[i], 0);
 			} else if (may_have_side_effects(op_array, ssa, &op_array->opcodes[i], &ssa->ops[i], ctx.reorder_dtor_effects)
 					|| zend_may_throw(&op_array->opcodes[i], op_array, ssa)
-					|| has_varargs) {
+					|| (has_varargs && may_break_varargs(op_array, ssa, &ssa->ops[i]))) {
 				add_operands_to_worklists(&ctx, &op_array->opcodes[i], &ssa->ops[i], 0);
 			} else {
 				zend_bitset_incl(ctx.instr_dead, i);

ext/opcache/Optimizer/zend_cfg.c

@@ -441,6 +441,9 @@ int zend_build_cfg(zend_arena **arena, const zend_op_array *op_array, uint32_t b
 					flags |= ZEND_FUNC_INDIRECT_VAR_ACCESS;
 				}
 				break;
+			case ZEND_FUNC_GET_ARGS:
+				flags |= ZEND_FUNC_VARARG;
+				break;
 		}
 	}
 
@@ -598,7 +601,8 @@ 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->dynamic = (flags & ZEND_FUNC_INDIRECT_VAR_ACCESS);
+	cfg->dynamic = (flags & ZEND_FUNC_INDIRECT_VAR_ACCESS) != 0;
+	cfg->vararg = (flags & ZEND_FUNC_VARARG) != 0;
 
 	if (func_flags) {
 		*func_flags |= flags;

ext/opcache/Optimizer/zend_cfg.h

@@ -93,6 +93,7 @@ typedef struct _zend_cfg {
 	unsigned int      split_at_calls : 1;
 	unsigned int      split_at_recv : 1;
 	unsigned int      dynamic : 1;        /* accesses varables by name   */
+	unsigned int      vararg : 1;         /* uses func_get_args()        */
 } zend_cfg;
 
 /* Build Flags */