From mboxrd@z Thu Jan 1 00:00:00 1970 From: Luc Van Oostenryck Subject: [PATCH 2/2] add warning option '-Wtautological-compare' Date: Wed, 7 Dec 2016 17:32:57 +0100 Message-ID: <20161207163257.22287-3-luc.vanoostenryck@gmail.com> References: <20161207163257.22287-1-luc.vanoostenryck@gmail.com> Return-path: Received: from mail-wm0-f67.google.com ([74.125.82.67]:35257 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932495AbcLGQdg (ORCPT ); Wed, 7 Dec 2016 11:33:36 -0500 Received: by mail-wm0-f67.google.com with SMTP id a20so28989636wme.2 for ; Wed, 07 Dec 2016 08:33:08 -0800 (PST) In-Reply-To: <20161207163257.22287-1-luc.vanoostenryck@gmail.com> Sender: linux-sparse-owner@vger.kernel.org List-Id: linux-sparse@vger.kernel.org To: linux-sparse@vger.kernel.org Cc: Christopher Li , Luc Van Oostenryck Now that we optimize away expressions like 'x == x' or 'x < x', also add a warning for it (but disabled by default). Signed-off-by: Luc Van Oostenryck --- lib.c | 2 ++ lib.h | 1 + simplify.c | 4 ++++ validation/tautological-compare.c | 35 +++++++++++++++++++++++++++++++++++ 4 files changed, 42 insertions(+) create mode 100644 validation/tautological-compare.c diff --git a/lib.c b/lib.c index e5b0bb63..6b7a0817 100644 --- a/lib.c +++ b/lib.c @@ -236,6 +236,7 @@ int Wptr_subtraction_blows = 0; int Wreturn_void = 0; int Wshadow = 0; int Wsizeof_bool = 0; +int Wtautological_compare = 0; int Wtransparent_union = 0; int Wtypesign = 0; int Wundef = 0; @@ -471,6 +472,7 @@ static const struct warning { { "return-void", &Wreturn_void }, { "shadow", &Wshadow }, { "sizeof-bool", &Wsizeof_bool }, + { "tautological-compare", &Wtautological_compare }, { "transparent-union", &Wtransparent_union }, { "typesign", &Wtypesign }, { "undef", &Wundef }, diff --git a/lib.h b/lib.h index 15b69fa2..130e5b6c 100644 --- a/lib.h +++ b/lib.h @@ -122,6 +122,7 @@ extern int Wptr_subtraction_blows; extern int Wreturn_void; extern int Wshadow; extern int Wsizeof_bool; +extern int Wtautological_compare; extern int Wtransparent_union; extern int Wtypesign; extern int Wundef; diff --git a/simplify.c b/simplify.c index fde72f0a..b29b3ebb 100644 --- a/simplify.c +++ b/simplify.c @@ -494,6 +494,8 @@ static int simplify_binop_same_args(struct instruction *insn, pseudo_t arg) case OP_SET_NE: case OP_SET_LT: case OP_SET_GT: case OP_SET_B: case OP_SET_A: + if (Wtautological_compare) + warning(insn->pos, "self-comparison always evaluates to false"); case OP_SUB: case OP_XOR: return replace_with_pseudo(insn, value_pseudo(0)); @@ -501,6 +503,8 @@ static int simplify_binop_same_args(struct instruction *insn, pseudo_t arg) case OP_SET_EQ: case OP_SET_LE: case OP_SET_GE: case OP_SET_BE: case OP_SET_AE: + if (Wtautological_compare) + warning(insn->pos, "self-comparison always evaluates to true"); return replace_with_pseudo(insn, value_pseudo(1)); case OP_AND: diff --git a/validation/tautological-compare.c b/validation/tautological-compare.c new file mode 100644 index 00000000..55a2b463 --- /dev/null +++ b/validation/tautological-compare.c @@ -0,0 +1,35 @@ +typedef unsigned int u32; + +int seq(int a) { return a == a; } +int sne(int a) { return a != a; } +int slt(int a) { return a < a; } +int sgt(int a) { return a > a; } +int sle(int a) { return a <= a; } +int sge(int a) { return a >= a; } + +u32 ueq(u32 a) { return a == a; } +u32 une(u32 a) { return a != a; } +u32 ult(u32 a) { return a < a; } +u32 ugt(u32 a) { return a > a; } +u32 ule(u32 a) { return a <= a; } +u32 uge(u32 a) { return a >= a; } + +/* + * check-name: tautological-compare + * check-command: sparse -Wno-decl -Wtautological-compare $file + * + * check-error-start +tautological-compare.c:3:30: warning: self-comparison always evaluates to true +tautological-compare.c:4:30: warning: self-comparison always evaluates to false +tautological-compare.c:5:29: warning: self-comparison always evaluates to false +tautological-compare.c:6:29: warning: self-comparison always evaluates to false +tautological-compare.c:7:30: warning: self-comparison always evaluates to true +tautological-compare.c:8:30: warning: self-comparison always evaluates to true +tautological-compare.c:10:30: warning: self-comparison always evaluates to true +tautological-compare.c:11:30: warning: self-comparison always evaluates to false +tautological-compare.c:12:29: warning: self-comparison always evaluates to false +tautological-compare.c:13:29: warning: self-comparison always evaluates to false +tautological-compare.c:14:30: warning: self-comparison always evaluates to true +tautological-compare.c:15:30: warning: self-comparison always evaluates to true + * check-error-end + */ -- 2.10.2