Module Name: src
Committed By: rillig
Date: Sat Aug 21 08:18:48 UTC 2021
Modified Files:
src/tests/usr.bin/xlint/lint1: msg_129.c msg_129.exp
src/usr.bin/xlint/lint1: tree.c
Log Message:
lint: do not warn about '(void)arg' and similar expressions
In the current NetBSD build, 5260 of the 46264 total lint warnings are
about expressions that have a null effect. Most of these occurrences
follow well-established patterns, which makes the warnings bogus.
Remove these warnings.
To generate a diff of this commit:
cvs rdiff -u -r1.4 -r1.5 src/tests/usr.bin/xlint/lint1/msg_129.c \
src/tests/usr.bin/xlint/lint1/msg_129.exp
cvs rdiff -u -r1.340 -r1.341 src/usr.bin/xlint/lint1/tree.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/tests/usr.bin/xlint/lint1/msg_129.c
diff -u src/tests/usr.bin/xlint/lint1/msg_129.c:1.4 src/tests/usr.bin/xlint/lint1/msg_129.c:1.5
--- src/tests/usr.bin/xlint/lint1/msg_129.c:1.4 Sat Aug 21 07:52:07 2021
+++ src/tests/usr.bin/xlint/lint1/msg_129.c Sat Aug 21 08:18:48 2021
@@ -1,4 +1,4 @@
-/* $NetBSD: msg_129.c,v 1.4 2021/08/21 07:52:07 rillig Exp $ */
+/* $NetBSD: msg_129.c,v 1.5 2021/08/21 08:18:48 rillig Exp $ */
# 3 "msg_129.c"
// Test for message: expression has null effect [129]
@@ -51,8 +51,6 @@ legitimate_use_cases(int arg)
* This expression is commonly used to mark the argument as
* deliberately unused.
*/
- /* TODO: remove this bogus warning. */
- /* expect+1: warning: expression has null effect [129] */
(void)arg;
/*
@@ -62,16 +60,20 @@ legitimate_use_cases(int arg)
* variants of the code, such as in debugging mode, and writing down
* the exact conditions would complicate the code unnecessarily.
*/
- /* TODO: remove this bogus warning. */
- /* expect+1: warning: expression has null effect [129] */
(void)local;
/* This is a short-hand notation for a do-nothing command. */
- /* TODO: remove this bogus warning. */
- /* expect+1: warning: expression has null effect [129] */
(void)0;
/*
+ * At the point where lint checks for expressions having a null
+ * effect, constants have been folded, therefore the following
+ * expression is considered safe as well. It does not appear in
+ * practice though.
+ */
+ (void)(3 - 3);
+
+ /*
* This variant of the do-nothing command is commonly used in
* preprocessor macros since it works nicely with if-else and if-then
* statements. It is longer than the above variant though.
@@ -81,9 +83,12 @@ legitimate_use_cases(int arg)
/*
* Only the expression '(void)0' is common, other expressions are
- * unusual enough that they warrant a warning.
+ * unusual enough to warrant a warning.
*/
- /* TODO: remove this bogus warning. */
/* expect+1: warning: expression has null effect [129] */
(void)13;
+
+ /* Double casts are unusual enough to warrant a warning. */
+ /* expect+1: warning: expression has null effect [129] */
+ (void)(void)0;
}
Index: src/tests/usr.bin/xlint/lint1/msg_129.exp
diff -u src/tests/usr.bin/xlint/lint1/msg_129.exp:1.4 src/tests/usr.bin/xlint/lint1/msg_129.exp:1.5
--- src/tests/usr.bin/xlint/lint1/msg_129.exp:1.4 Sat Aug 21 07:52:07 2021
+++ src/tests/usr.bin/xlint/lint1/msg_129.exp Sat Aug 21 08:18:48 2021
@@ -1,6 +1,4 @@
msg_129.c(37): warning: expression has null effect [129]
msg_129.c(41): warning: expression has null effect [129]
-msg_129.c(56): warning: expression has null effect [129]
-msg_129.c(67): warning: expression has null effect [129]
-msg_129.c(72): warning: expression has null effect [129]
-msg_129.c(88): warning: expression has null effect [129]
+msg_129.c(89): warning: expression has null effect [129]
+msg_129.c(93): warning: expression has null effect [129]
Index: src/usr.bin/xlint/lint1/tree.c
diff -u src/usr.bin/xlint/lint1/tree.c:1.340 src/usr.bin/xlint/lint1/tree.c:1.341
--- src/usr.bin/xlint/lint1/tree.c:1.340 Thu Aug 19 21:13:58 2021
+++ src/usr.bin/xlint/lint1/tree.c Sat Aug 21 08:18:48 2021
@@ -1,4 +1,4 @@
-/* $NetBSD: tree.c,v 1.340 2021/08/19 21:13:58 rillig Exp $ */
+/* $NetBSD: tree.c,v 1.341 2021/08/21 08:18:48 rillig Exp $ */
/*
* Copyright (c) 1994, 1995 Jochen Pohl
@@ -37,7 +37,7 @@
#include <sys/cdefs.h>
#if defined(__RCSID) && !defined(lint)
-__RCSID("$NetBSD: tree.c,v 1.340 2021/08/19 21:13:58 rillig Exp $");
+__RCSID("$NetBSD: tree.c,v 1.341 2021/08/21 08:18:48 rillig Exp $");
#endif
#include <float.h>
@@ -3801,14 +3801,47 @@ has_side_effect(const tnode_t *tn) // NO
return false;
}
+static bool
+is_void_cast(const tnode_t *tn)
+{
+
+ return tn->tn_op == CVT && tn->tn_cast &&
+ tn->tn_type->t_tspec == VOID;
+}
+
+static bool
+is_local_symbol(const tnode_t *tn)
+{
+
+ return tn->tn_op == LOAD &&
+ tn->tn_left->tn_op == NAME &&
+ tn->tn_left->tn_sym->s_scl == AUTO;
+}
+
+static bool
+is_int_constant_zero(const tnode_t *tn)
+{
+
+ return tn->tn_op == CON &&
+ tn->tn_type->t_tspec == INT &&
+ tn->tn_val->v_quad == 0;
+}
+
static void
check_null_effect(const tnode_t *tn)
{
- if (hflag && !has_side_effect(tn)) {
- /* expression has null effect */
- warning(129);
- }
+ if (!hflag)
+ return;
+ if ( has_side_effect(tn))
+ return;
+ if (is_void_cast(tn) && is_local_symbol(tn->tn_left))
+ return;
+ if (is_void_cast(tn) && is_int_constant_zero(tn->tn_left))
+ return;
+
+ /* expression has null effect */
+ warning(129);
}
/* ARGSUSED */
