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https://github.com/Gericom/teak-llvm.git
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c5417aafec
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 llvm-svn: 321691
293 lines
5.7 KiB
C
293 lines
5.7 KiB
C
// RUN: %clang_cc1 -fsyntax-only \
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// RUN: -Wtautological-unsigned-zero-compare \
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// RUN: -verify %s
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// RUN: %clang_cc1 -fsyntax-only \
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// RUN: -verify=silence %s
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// RUN: %clang_cc1 -fsyntax-only \
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// RUN: -Wtautological-unsigned-zero-compare \
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// RUN: -verify -x c++ %s
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// RUN: %clang_cc1 -fsyntax-only \
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// RUN: -verify=silence -x c++ %s
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unsigned uvalue(void);
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signed int svalue(void);
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#define macro(val) val
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#ifdef __cplusplus
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template<typename T>
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void TFunc() {
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// Make sure that we do warn for normal variables in template functions !
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unsigned char c = svalue();
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if (c < 0) // expected-warning {{comparison of unsigned expression < 0 is always false}}
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return;
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if (c < macro(0))
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return;
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T v = svalue();
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if (v < 0)
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return;
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}
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#endif
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int main()
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{
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#ifdef __cplusplus
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TFunc<unsigned char>();
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TFunc<unsigned short>();
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#endif
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short s = svalue();
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unsigned un = uvalue();
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// silence-no-diagnostics
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// Note: both sides are promoted to unsigned long prior to the comparison.
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if (s == 0UL)
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return 0;
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if (s != 0UL)
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return 0;
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if (s < 0UL) // expected-warning {{comparison of unsigned expression < 0 is always false}}
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return 0;
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if (s <= 0UL)
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return 0;
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if (s > 0UL)
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return 0;
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if (s >= 0UL) // expected-warning {{comparison of unsigned expression >= 0 is always true}}
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return 0;
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if (0UL == s)
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return 0;
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if (0UL != s)
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return 0;
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if (0UL < s)
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return 0;
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if (0UL <= s) // expected-warning {{comparison of 0 <= unsigned expression is always true}}
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return 0;
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if (0UL > s) // expected-warning {{comparison of 0 > unsigned expression is always false}}
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return 0;
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if (0UL >= s)
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return 0;
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if (un == 0)
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return 0;
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if (un != 0)
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return 0;
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if (un < 0) // expected-warning {{comparison of unsigned expression < 0 is always false}}
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return 0;
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if (un <= 0)
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return 0;
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if (un > 0)
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return 0;
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if (un >= 0) // expected-warning {{comparison of unsigned expression >= 0 is always true}}
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return 0;
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if (0 == un)
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return 0;
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if (0 != un)
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return 0;
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if (0 < un)
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return 0;
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if (0 <= un) // expected-warning {{comparison of 0 <= unsigned expression is always true}}
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return 0;
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if (0 > un) // expected-warning {{comparison of 0 > unsigned expression is always false}}
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return 0;
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if (0 >= un)
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return 0;
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if (un == 0UL)
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return 0;
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if (un != 0UL)
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return 0;
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if (un < 0UL) // expected-warning {{comparison of unsigned expression < 0 is always false}}
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return 0;
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if (un <= 0UL)
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return 0;
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if (un > 0UL)
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return 0;
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if (un >= 0UL) // expected-warning {{comparison of unsigned expression >= 0 is always true}}
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return 0;
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if (0UL == un)
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return 0;
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if (0UL != un)
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return 0;
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if (0UL < un)
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return 0;
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if (0UL <= un) // expected-warning {{comparison of 0 <= unsigned expression is always true}}
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return 0;
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if (0UL > un) // expected-warning {{comparison of 0 > unsigned expression is always false}}
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return 0;
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if (0UL >= un)
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return 0;
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signed int a = svalue();
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if (a == 0)
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return 0;
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if (a != 0)
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return 0;
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if (a < 0)
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return 0;
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if (a <= 0)
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return 0;
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if (a > 0)
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return 0;
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if (a >= 0)
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return 0;
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if (0 == a)
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return 0;
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if (0 != a)
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return 0;
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if (0 < a)
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return 0;
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if (0 <= a)
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return 0;
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if (0 > a)
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return 0;
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if (0 >= a)
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return 0;
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if (a == 0UL)
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return 0;
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if (a != 0UL)
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return 0;
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if (a < 0UL) // expected-warning {{comparison of unsigned expression < 0 is always false}}
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return 0;
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if (a <= 0UL)
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return 0;
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if (a > 0UL)
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return 0;
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if (a >= 0UL) // expected-warning {{comparison of unsigned expression >= 0 is always true}}
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return 0;
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if (0UL == a)
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return 0;
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if (0UL != a)
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return 0;
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if (0UL < a)
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return 0;
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if (0UL <= a) // expected-warning {{comparison of 0 <= unsigned expression is always true}}
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return 0;
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if (0UL > a) // expected-warning {{comparison of 0 > unsigned expression is always false}}
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return 0;
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if (0UL >= a)
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return 0;
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float fl = 0;
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if (fl == 0)
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return 0;
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if (fl != 0)
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return 0;
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if (fl < 0)
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return 0;
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if (fl <= 0)
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return 0;
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if (fl > 0)
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return 0;
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if (fl >= 0)
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return 0;
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if (0 == fl)
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return 0;
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if (0 != fl)
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return 0;
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if (0 < fl)
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return 0;
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if (0 <= fl)
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return 0;
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if (0 > fl)
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return 0;
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if (0 >= fl)
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return 0;
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if (fl == 0UL)
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return 0;
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if (fl != 0UL)
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return 0;
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if (fl < 0UL)
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return 0;
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if (fl <= 0UL)
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return 0;
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if (fl > 0UL)
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return 0;
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if (fl >= 0UL)
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return 0;
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if (0UL == fl)
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return 0;
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if (0UL != fl)
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return 0;
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if (0UL < fl)
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return 0;
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if (0UL <= fl)
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return 0;
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if (0UL > fl)
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return 0;
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if (0UL >= fl)
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return 0;
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double dl = 0;
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if (dl == 0)
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return 0;
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if (dl != 0)
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return 0;
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if (dl < 0)
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return 0;
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if (dl <= 0)
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return 0;
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if (dl > 0)
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return 0;
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if (dl >= 0)
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return 0;
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if (0 == dl)
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return 0;
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if (0 != dl)
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return 0;
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if (0 < dl)
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return 0;
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if (0 <= dl)
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return 0;
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if (0 > dl)
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return 0;
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if (0 >= dl)
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return 0;
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if (dl == 0UL)
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return 0;
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if (dl != 0UL)
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return 0;
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if (dl < 0UL)
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return 0;
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if (dl <= 0UL)
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return 0;
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if (dl > 0UL)
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return 0;
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if (dl >= 0UL)
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return 0;
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if (0UL == dl)
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return 0;
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if (0UL != dl)
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return 0;
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if (0UL < dl)
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return 0;
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if (0UL <= dl)
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return 0;
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if (0UL > dl)
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return 0;
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if (0UL >= dl)
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return 0;
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return 1;
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}
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