r321691 - [Sema] -Wtautological-constant-compare is too good. Cripple it.
Roman Lebedev via cfe-commits
cfe-commits at lists.llvm.org
Wed Jan 3 00:45:19 PST 2018
Author: lebedevri
Date: Wed Jan 3 00:45:19 2018
New Revision: 321691
URL: http://llvm.org/viewvc/llvm-project?rev=321691&view=rev
Log:
[Sema] -Wtautological-constant-compare is too good. Cripple it.
Summary:
The diagnostic was mostly introduced in D38101 by me, as a reaction to wasting a lot of time, see [[ https://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20171009/206427.html | mail ]].
However, the diagnostic is pretty dumb. While it works with no false-positives,
there are some questionable cases that are diagnosed when one would argue that they should not be.
The common complaint is that it diagnoses the comparisons between an `int` and
`long` when compiling for a 32-bit target as tautological, but not when
compiling for 64-bit targets. The underlying problem is obvious: data model.
In most cases, 64-bit target is `LP64` (`int` is 32-bit, `long` and pointer are
64-bit), and the 32-bit target is `ILP32` (`int`, `long`, and pointer are 32-bit).
I.e. the common pattern is: (pseudocode)
```
#include <limits>
#include <cstdint>
int main() {
using T1 = long;
using T2 = int;
T1 r;
if (r < std::numeric_limits<T2>::min()) {}
if (r > std::numeric_limits<T2>::max()) {}
}
```
As an example, D39149 was trying to fix this diagnostic in libc++, and it was not well-received.
This *could* be "fixed", by changing the diagnostics logic to something like
`if the types of the values being compared are different, but are of the same size, then do diagnose`,
and i even attempted to do so in D39462, but as @rjmccall rightfully commented,
that implementation is incomplete to say the least.
So to stop causing trouble, and avoid contaminating upcoming release, lets do this workaround:
* move these three diags (`warn_unsigned_always_true_comparison`, `warn_unsigned_enum_always_true_comparison`, `warn_tautological_constant_compare`) into it's own `-Wtautological-constant-in-range-compare`
* Disable them by default
* Make them part of `-Wextra`
* Additionally, give `warn_tautological_constant_compare` it's own flag `-Wtautological-type-limit-compare`.
I'm not happy about that name, but i can't come up with anything better.
This way all three of them can be enabled/disabled either altogether, or one-by-one.
Reviewers: aaron.ballman, rsmith, smeenai, rjmccall, rnk, mclow.lists, dim
Reviewed By: aaron.ballman, rsmith, dim
Subscribers: thakis, compnerd, mehdi_amini, dim, hans, cfe-commits, rjmccall
Tags: #clang
Differential Revision: https://reviews.llvm.org/D41512
Modified:
cfe/trunk/include/clang/Basic/DiagnosticGroups.td
cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
cfe/trunk/test/Sema/compare.c
cfe/trunk/test/Sema/tautological-constant-compare.c
cfe/trunk/test/Sema/tautological-constant-enum-compare.c
cfe/trunk/test/Sema/tautological-unsigned-enum-zero-compare.c
cfe/trunk/test/Sema/tautological-unsigned-enum-zero-compare.cpp
cfe/trunk/test/Sema/tautological-unsigned-zero-compare.c
cfe/trunk/test/SemaCXX/compare.cpp
Modified: cfe/trunk/include/clang/Basic/DiagnosticGroups.td
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticGroups.td?rev=321691&r1=321690&r2=321691&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticGroups.td (original)
+++ cfe/trunk/include/clang/Basic/DiagnosticGroups.td Wed Jan 3 00:45:19 2018
@@ -435,12 +435,16 @@ def StringCompare : DiagGroup<"string-co
def StringPlusInt : DiagGroup<"string-plus-int">;
def StringPlusChar : DiagGroup<"string-plus-char">;
def StrncatSize : DiagGroup<"strncat-size">;
+def TautologicalTypeLimitCompare : DiagGroup<"tautological-type-limit-compare">;
def TautologicalUnsignedZeroCompare : DiagGroup<"tautological-unsigned-zero-compare">;
def TautologicalUnsignedEnumZeroCompare : DiagGroup<"tautological-unsigned-enum-zero-compare">;
+def TautologicalInRangeCompare : DiagGroup<"tautological-constant-in-range-compare",
+ [TautologicalTypeLimitCompare,
+ TautologicalUnsignedZeroCompare,
+ TautologicalUnsignedEnumZeroCompare]>;
def TautologicalOutOfRangeCompare : DiagGroup<"tautological-constant-out-of-range-compare">;
def TautologicalConstantCompare : DiagGroup<"tautological-constant-compare",
- [TautologicalUnsignedZeroCompare,
- TautologicalUnsignedEnumZeroCompare,
+ [TautologicalInRangeCompare,
TautologicalOutOfRangeCompare]>;
def TautologicalPointerCompare : DiagGroup<"tautological-pointer-compare">;
def TautologicalOverlapCompare : DiagGroup<"tautological-overlap-compare">;
@@ -715,6 +719,7 @@ def IntToPointerCast : DiagGroup<"int-to
def Move : DiagGroup<"move", [PessimizingMove, RedundantMove, SelfMove]>;
def Extra : DiagGroup<"extra", [
+ TautologicalInRangeCompare,
MissingFieldInitializers,
IgnoredQualifiers,
InitializerOverrides,
Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=321691&r1=321690&r2=321691&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)
+++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Wed Jan 3 00:45:19 2018
@@ -5946,15 +5946,15 @@ def note_typecheck_assign_const : Note<
def warn_unsigned_always_true_comparison : Warning<
"result of comparison of %select{%3|unsigned expression}0 %2 "
"%select{unsigned expression|%3}0 is always %4">,
- InGroup<TautologicalUnsignedZeroCompare>;
+ InGroup<TautologicalUnsignedZeroCompare>, DefaultIgnore;
def warn_unsigned_enum_always_true_comparison : Warning<
"result of comparison of %select{%3|unsigned enum expression}0 %2 "
"%select{unsigned enum expression|%3}0 is always %4">,
- InGroup<TautologicalUnsignedEnumZeroCompare>;
+ InGroup<TautologicalUnsignedEnumZeroCompare>, DefaultIgnore;
def warn_tautological_constant_compare : Warning<
"result of comparison %select{%3|%1}0 %2 "
"%select{%1|%3}0 is always %4">,
- InGroup<TautologicalConstantCompare>;
+ InGroup<TautologicalTypeLimitCompare>, DefaultIgnore;
def warn_mixed_sign_comparison : Warning<
"comparison of integers of different signs: %0 and %1">,
Modified: cfe/trunk/test/Sema/compare.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/compare.c?rev=321691&r1=321690&r2=321691&view=diff
==============================================================================
--- cfe/trunk/test/Sema/compare.c (original)
+++ cfe/trunk/test/Sema/compare.c Wed Jan 3 00:45:19 2018
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -triple x86_64-apple-darwin -fsyntax-only -pedantic -verify -Wsign-compare %s -Wno-unreachable-code
+// RUN: %clang_cc1 -triple x86_64-apple-darwin -fsyntax-only -pedantic -verify -Wsign-compare -Wtautological-constant-in-range-compare %s -Wno-unreachable-code
int test(char *C) { // nothing here should warn.
return C != ((void*)0);
Modified: cfe/trunk/test/Sema/tautological-constant-compare.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/tautological-constant-compare.c?rev=321691&r1=321690&r2=321691&view=diff
==============================================================================
--- cfe/trunk/test/Sema/tautological-constant-compare.c (original)
+++ cfe/trunk/test/Sema/tautological-constant-compare.c Wed Jan 3 00:45:19 2018
@@ -1,7 +1,13 @@
-// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -DTEST -verify %s
-// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -Wno-tautological-constant-compare -verify %s
-// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -DTEST -verify -x c++ %s
-// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -Wno-tautological-constant-compare -verify -x c++ %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -Wtautological-constant-in-range-compare -DTEST -verify %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -Wtautological-constant-in-range-compare -DTEST -verify -x c++ %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -Wtautological-type-limit-compare -DTEST -verify %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -Wtautological-type-limit-compare -DTEST -verify -x c++ %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -Wextra -Wno-sign-compare -DTEST -verify %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -Wextra -Wno-sign-compare -DTEST -verify -x c++ %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -Wall -verify %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -Wall -verify -x c++ %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -verify -x c++ %s
int value(void);
@@ -122,32 +128,6 @@ int main()
if (32767UL >= s)
return 0;
- if (s == 0UL)
- return 0;
- if (s != 0UL)
- return 0;
- if (s < 0UL) // expected-warning {{comparison of unsigned expression < 0 is always false}}
- return 0;
- if (s <= 0UL)
- return 0;
- if (s > 0UL)
- return 0;
- if (s >= 0UL) // expected-warning {{comparison of unsigned expression >= 0 is always true}}
- return 0;
-
- if (0UL == s)
- return 0;
- if (0UL != s)
- return 0;
- if (0UL < s)
- return 0;
- if (0UL <= s) // expected-warning {{comparison of 0 <= unsigned expression is always true}}
- return 0;
- if (0UL > s) // expected-warning {{comparison of 0 > unsigned expression is always false}}
- return 0;
- if (0UL >= s)
- return 0;
-
enum { ULONG_MAX = (2UL * (unsigned long)__LONG_MAX__ + 1UL) };
if (s == 2UL * (unsigned long)__LONG_MAX__ + 1UL)
return 0;
@@ -498,7 +478,7 @@ int main()
return 0;
#if __SIZEOF_INT128__
- __int128 i128;
+ __int128 i128 = value();
if (i128 == -1) // used to crash
return 0;
#endif
@@ -509,7 +489,7 @@ int main()
no,
maybe
};
- enum E e;
+ enum E e = (enum E)value();
if (e == yes)
return 0;
Modified: cfe/trunk/test/Sema/tautological-constant-enum-compare.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/tautological-constant-enum-compare.c?rev=321691&r1=321690&r2=321691&view=diff
==============================================================================
--- cfe/trunk/test/Sema/tautological-constant-enum-compare.c (original)
+++ cfe/trunk/test/Sema/tautological-constant-enum-compare.c Wed Jan 3 00:45:19 2018
@@ -1,5 +1,5 @@
-// RUN: %clang_cc1 -triple=x86_64-pc-linux-gnu -fsyntax-only -DUNSIGNED -verify %s
-// RUN: %clang_cc1 -triple=x86_64-pc-win32 -fsyntax-only -DSIGNED -verify %s
+// RUN: %clang_cc1 -triple=x86_64-pc-linux-gnu -fsyntax-only -DUNSIGNED -Wtautological-constant-in-range-compare -verify %s
+// RUN: %clang_cc1 -triple=x86_64-pc-win32 -fsyntax-only -DSIGNED -Wtautological-constant-in-range-compare -verify %s
// RUN: %clang_cc1 -triple=x86_64-pc-linux-gnu -fsyntax-only -DUNSIGNED -DSILENCE -Wno-tautological-constant-compare -verify %s
// RUN: %clang_cc1 -triple=x86_64-pc-win32 -fsyntax-only -DSIGNED -DSILENCE -Wno-tautological-constant-compare -verify %s
Modified: cfe/trunk/test/Sema/tautological-unsigned-enum-zero-compare.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/tautological-unsigned-enum-zero-compare.c?rev=321691&r1=321690&r2=321691&view=diff
==============================================================================
--- cfe/trunk/test/Sema/tautological-unsigned-enum-zero-compare.c (original)
+++ cfe/trunk/test/Sema/tautological-unsigned-enum-zero-compare.c Wed Jan 3 00:45:19 2018
@@ -1,9 +1,10 @@
// RUN: %clang_cc1 -triple=x86_64-pc-linux-gnu -fsyntax-only \
+// RUN: -Wtautological-unsigned-enum-zero-compare \
// RUN: -verify=unsigned,unsigned-signed %s
// RUN: %clang_cc1 -triple=x86_64-pc-win32 -fsyntax-only \
+// RUN: -Wtautological-unsigned-enum-zero-compare \
// RUN: -verify=unsigned-signed %s
// RUN: %clang_cc1 -triple=x86_64-pc-win32 -fsyntax-only \
-// RUN: -Wno-tautological-unsigned-enum-zero-compare \
// RUN: -verify=silence %s
// Okay, this is where it gets complicated.
Modified: cfe/trunk/test/Sema/tautological-unsigned-enum-zero-compare.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/tautological-unsigned-enum-zero-compare.cpp?rev=321691&r1=321690&r2=321691&view=diff
==============================================================================
--- cfe/trunk/test/Sema/tautological-unsigned-enum-zero-compare.cpp (original)
+++ cfe/trunk/test/Sema/tautological-unsigned-enum-zero-compare.cpp Wed Jan 3 00:45:19 2018
@@ -1,9 +1,10 @@
// RUN: %clang_cc1 -std=c++11 -triple=x86_64-pc-linux-gnu -fsyntax-only \
+// RUN: -Wtautological-unsigned-enum-zero-compare \
// RUN: -verify=unsigned,unsigned-signed %s
// RUN: %clang_cc1 -std=c++11 -triple=x86_64-pc-win32 -fsyntax-only \
+// RUN: -Wtautological-unsigned-enum-zero-compare \
// RUN: -verify=unsigned-signed %s
// RUN: %clang_cc1 -std=c++11 -triple=x86_64-pc-win32 -fsyntax-only \
-// RUN: -Wno-tautological-unsigned-enum-zero-compare \
// RUN: -verify=silence %s
// silence-no-diagnostics
Modified: cfe/trunk/test/Sema/tautological-unsigned-zero-compare.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/tautological-unsigned-zero-compare.c?rev=321691&r1=321690&r2=321691&view=diff
==============================================================================
--- cfe/trunk/test/Sema/tautological-unsigned-zero-compare.c (original)
+++ cfe/trunk/test/Sema/tautological-unsigned-zero-compare.c Wed Jan 3 00:45:19 2018
@@ -1,7 +1,13 @@
-// RUN: %clang_cc1 -fsyntax-only -verify %s
-// RUN: %clang_cc1 -fsyntax-only -Wno-tautological-unsigned-zero-compare -verify=silence %s
-// RUN: %clang_cc1 -fsyntax-only -verify -x c++ %s
-// RUN: %clang_cc1 -fsyntax-only -Wno-tautological-unsigned-zero-compare -verify=silence -x c++ %s
+// RUN: %clang_cc1 -fsyntax-only \
+// RUN: -Wtautological-unsigned-zero-compare \
+// RUN: -verify %s
+// RUN: %clang_cc1 -fsyntax-only \
+// RUN: -verify=silence %s
+// RUN: %clang_cc1 -fsyntax-only \
+// RUN: -Wtautological-unsigned-zero-compare \
+// RUN: -verify -x c++ %s
+// RUN: %clang_cc1 -fsyntax-only \
+// RUN: -verify=silence -x c++ %s
unsigned uvalue(void);
signed int svalue(void);
@@ -32,10 +38,39 @@ int main()
TFunc<unsigned short>();
#endif
+ short s = svalue();
+
unsigned un = uvalue();
// silence-no-diagnostics
+ // Note: both sides are promoted to unsigned long prior to the comparison.
+ if (s == 0UL)
+ return 0;
+ if (s != 0UL)
+ return 0;
+ if (s < 0UL) // expected-warning {{comparison of unsigned expression < 0 is always false}}
+ return 0;
+ if (s <= 0UL)
+ return 0;
+ if (s > 0UL)
+ return 0;
+ if (s >= 0UL) // expected-warning {{comparison of unsigned expression >= 0 is always true}}
+ return 0;
+
+ if (0UL == s)
+ return 0;
+ if (0UL != s)
+ return 0;
+ if (0UL < s)
+ return 0;
+ if (0UL <= s) // expected-warning {{comparison of 0 <= unsigned expression is always true}}
+ return 0;
+ if (0UL > s) // expected-warning {{comparison of 0 > unsigned expression is always false}}
+ return 0;
+ if (0UL >= s)
+ return 0;
+
if (un == 0)
return 0;
if (un != 0)
Modified: cfe/trunk/test/SemaCXX/compare.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/compare.cpp?rev=321691&r1=321690&r2=321691&view=diff
==============================================================================
--- cfe/trunk/test/SemaCXX/compare.cpp (original)
+++ cfe/trunk/test/SemaCXX/compare.cpp Wed Jan 3 00:45:19 2018
@@ -1,7 +1,7 @@
// Force x86-64 because some of our heuristics are actually based
// on integer sizes.
-// RUN: %clang_cc1 -triple x86_64-apple-darwin -fsyntax-only -pedantic -verify -Wsign-compare -std=c++11 %s
+// RUN: %clang_cc1 -triple x86_64-apple-darwin -fsyntax-only -pedantic -verify -Wsign-compare -Wtautological-constant-in-range-compare -std=c++11 %s
int test0(long a, unsigned long b) {
enum EnumA {A};
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