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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
128 lines
3.1 KiB
C
128 lines
3.1 KiB
C
// RUN: %clang_cc1 -triple=x86_64-pc-linux-gnu -fsyntax-only \
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// RUN: -Wtautological-unsigned-enum-zero-compare \
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// RUN: -verify=unsigned,unsigned-signed %s
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// RUN: %clang_cc1 -triple=x86_64-pc-win32 -fsyntax-only \
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// RUN: -Wtautological-unsigned-enum-zero-compare \
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// RUN: -verify=unsigned-signed %s
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// RUN: %clang_cc1 -triple=x86_64-pc-win32 -fsyntax-only \
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// RUN: -verify=silence %s
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// Okay, this is where it gets complicated.
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// Then default enum sigdness is target-specific.
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// On windows, it is signed by default. We do not want to warn in that case.
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int main() {
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enum A { A_a = 0 };
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enum A a;
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enum B { B_a = -1 };
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enum B b;
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// silence-no-diagnostics
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if (a < 0) // unsigned-warning {{comparison of unsigned enum expression < 0 is always false}}
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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 > 0)
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return 0;
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if (0 <= a) // unsigned-warning {{comparison of 0 <= unsigned enum expression is always true}}
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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) // unsigned-warning {{comparison of 0 > unsigned enum expression is always false}}
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return 0;
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if (a >= 0) // unsigned-warning {{comparison of unsigned enum expression >= 0 is always true}}
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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 < 0U) // unsigned-signed-warning {{comparison of unsigned enum expression < 0 is always false}}
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return 0;
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if (0U >= a)
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return 0;
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if (a > 0U)
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return 0;
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if (0U <= a) // unsigned-signed-warning {{comparison of 0 <= unsigned enum expression is always true}}
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return 0;
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if (a <= 0U)
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return 0;
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if (0U > a) // unsigned-signed-warning {{comparison of 0 > unsigned enum expression is always false}}
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return 0;
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if (a >= 0U) // unsigned-signed-warning {{comparison of unsigned enum expression >= 0 is always true}}
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return 0;
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if (0U < a)
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return 0;
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if (b < 0)
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return 0;
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if (0 >= b)
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return 0;
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if (b > 0)
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return 0;
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if (0 <= b)
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return 0;
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if (b <= 0)
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return 0;
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if (0 > b)
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return 0;
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if (b >= 0)
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return 0;
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if (0 < b)
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return 0;
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if (b < 0U) // unsigned-signed-warning {{comparison of unsigned enum expression < 0 is always false}}
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return 0;
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if (0U >= b)
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return 0;
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if (b > 0U)
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return 0;
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if (0U <= b) // unsigned-signed-warning {{comparison of 0 <= unsigned enum expression is always true}}
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return 0;
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if (b <= 0U)
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return 0;
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if (0U > b) // unsigned-signed-warning {{comparison of 0 > unsigned enum expression is always false}}
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return 0;
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if (b >= 0U) // unsigned-signed-warning {{comparison of unsigned enum expression >= 0 is always true}}
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return 0;
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if (0U < b)
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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 (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 (a == 0U)
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return 0;
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if (0U != a)
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return 0;
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if (a != 0U)
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return 0;
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if (0U == a)
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return 0;
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if (b == 0)
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return 0;
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if (0 != b)
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return 0;
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if (b != 0)
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return 0;
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if (0 == b)
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return 0;
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if (b == 0U)
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return 0;
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if (0U != b)
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return 0;
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if (b != 0U)
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return 0;
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if (0U == b)
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return 0;
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return 1;
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}
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